Hóa bảo vệ thực vật

B GIO DC V O TO -------------------------------------------------------------------------------------------------TRNG I HC CN TH KHOA NNG NGHIP & SINH HC NG DNG B MN BO V THC VTng 3/2, khu 2, Tp. Cn Th. E-mail: [email protected], Cell phone: 0913 675 024

GIO TRNH HA BO V THC VT

PGs. Ts. TRN VN HAI

Nm 2009

THNG TIN V TC GI PHM VI V I TNG S DNG CA GIO TRNH HA BO V THC VT I.THNG TIN V TC GI H v tn: TRN VN HAI Sinh nm: 02-03-1955 C quan cng tc: B Mn Bo V Thc Vt, Khoa Nng Nghip v Sinh Hc ng Dng, Trng i Hc Cn Th E-mail: [email protected] II.PHM VI V I TNG S DNG -Gio trnh c th s dng cho cc ngnh: Nng hc, Trng trt, Bo v thc vt, Kinh t nng nghip, K thut nng nghip v S phm ha. -C th dng cho cc trng: Trung hc k thut, i hc nng nghip, S phm -Cc t kha: cn trng, bnh cy, c di, thuc tr dch hi, bo v thc vt, c cht, th nghim, hu hiu, d lng. hot cht -Yu cu kin thc trc khi hc mn ny: cn trng, bnh cy, c di v ha hc hu c. - in thnh gio trnh ti th vin i hc Cn Th

MC LCCHNG M U ...................................................................................................................... 1 I. V TR v VAI TR CA MN HC .................................................................................. 1 1. Dch hi v mc tc hi ................................................................................................. 1 2. Cc bin php bo v thc vt ............................................................................................ 1 3. u im, nhc im v v tr ca ngnh Ha BVTV hin nay ........................................ 2 II. Lch s php trin ngnh Ha BVTV .................................................................................... 3 III. C s mc ch v i tng mn hc ................................................................................. 4 Cu hi n tp ............................................................................................................................. 4

CHNG 1: C CHT HC NNG NGHIP ........................................................................ 5 1.1 CC KHI NIM V CHT C v S NHIM C.................................................. 5 1.1.1 Cc khi nim c bn..................................................................................................... 5 1.1.2 Nhng yu cu i vi mt ha cht dng trong bo v thc vt ................................. 6 1.1.3 Phn loi thuc tr dch hi ........................................................................................... 7 1.2 S XM NHP CA CHT C VO C TH SINH VT........................................ 9 1.2.1 S xm nhp ca cht c vo t bo .......................................................................... 10 1.2.2 S xm nhp ca cht c vo c th cn trng.......................................................... 10 1.2.3 S xm nhp ca cht c v c th loi gm nhm ................................................... 11 1.3.2 S bin i ca cht c trong t bo sinh vt ............................................................ 12 1.3.3 Cc hnh thc tc ng ca cht c ........................................................................... 13 1.3.4 Tc ng ca cht c n dch hi ............................................................................. 14 1.4 NHNG NHN T NH HNG N TNH C CA CHT C...................... 15 1.4.1 S lin quan gia tnh cht ca cht c v tnh c ca cht c.............................. 15 1.4.2 S lin quan gia c im ca sinh vt vi tnh c ca cht c ............................ 16 1.4.3 nh hng ca mt s ngoi cnh n tnh c ca cht c..................................... 19 1.5 THUC BO V THC VT V S BIN I CU TRC QUN TH SINH VT ................................................................................................................................................... 20 1.5.1 Thuc BVTV vi qun th dch hi............................................................................. 21 1.5.2 Thuc bo v thc vt vi nhng sinh vt c ch ........................................................ 21 1.5.3 Thuc bo v thc vt i vi cy trng ..................................................................... 21 Cu hi n tp ........................................................................................................................... 22

CHNG 2: CC PHNG PHP S DNG v TH NGHIM THUC TR DCH HI ....................................................................................................................................................... 23 2.1 CC DNG CH PHM DNG TRONG BO V THC VT.................................. 23 2.1.1 Nhng ch phm cn ha long trc khi s dng ..................................................... 24 2.2.2 Nhng ch phm khng ha long trc khi p dng ................................................. 24 2.2.3 Cht ph gia ................................................................................................................. 25 2.2 CC PHNG PHP S DNG THUC TR DCH HI ......................................... 26 2.2.1 Phun thuc ................................................................................................................... 26 2.2.2 Rc ht ......................................................................................................................... 30 2.2.3 Ni liu php thc vt.................................................................................................. 30 2.2.4 Xng hi ...................................................................................................................... 31 2.2.5 X l ging .................................................................................................................. 32 2.2.6 Lm b c................................................................................................................... 33 2.3 CC PHNG PHP XC NH TNH C V HIU LC CA THUC TR DCH HI................................................................................................................................. 33 A. CC PHNG PHP XC NH TNH C CA THUC TR DCH HI TRONG PHNG TH NGHIM ............................................................................................................ 34 2.3.1 Nguyn tc th nghim ................................................................................................. 34 2.3.2 Phng php xc nh tnh c ca thuc tr su ....................................................... 34 2.3.3 Phng php xc nh tnh c ca thuc tr nm...................................................... 35 2.3.4 Phng php xc nh tnh c ca thuc tr c......................................................... 36 B. CC PHNG PHP XC NH HIU LC CA THUC TR DCH HI TRN NG RUNG........................................................................................................................ 37 2.3.5 B tr th nghim .......................................................................................................... 37 2.3.6 Xc nh hiu qu ca vic dng thuc tr dch hi.................................................... 38 C. CC PHNG PHP TNH TON HIU QU DNG THUC .................................. 39 2.3.7 hiu ca thuc tr su ............................................................................................ 39 2.3.8 Ch tiu nh gi thuc tr nm................................................................................... 42 2.3.9 Ch tiu nh gi thuc tr c...................................................................................... 42 D. SO SNH TNH C CA CC LOI THUC TR DCH HI ............................... 43 Cu hi n tp ........................................................................................................................... 44

CHNG 3: THUC TR DCH HI ...................................................................................... 44 A. THUC TR SU.............................................................................................................. 44 3.1 THUC TR SU CLO HU C ................................................................................... 44 3.1.1 U IM ............................................................................................................................ 44 3.1.2 NHC IM.................................................................................................................... 44 3.1.3 MT S C IM KHC.............................................................................................. 44 3.1.4 DDT (Dichlodiphenyl trichloetan)....................................................................................... 45 3.1.5 BHC ..................................................................................................................................... 46 3.1.6 THUC TR SU TECPEN CLO HA........................................................................... 47 3.1.7 THUC TR SU CYCLODIEN ..................................................................................... 47 3.2 THUC TR SU GC LN HU C ......................................................................... 49 3.2.1 METHYL PARATHION (MP) (Metaphos, Wofatox, Folidon M, Metacid, Bladan - M).. 50 3.2.2 SUMITHION (Fenitrothion, Metathion, Methylnitrophos, Folithion)................................ 51 3.2.3 LEBAYCID (Fenthion, Mertophos, Baycid, Baytex) ......................................................... 51 3.2.4 BASUDIN (Diazinon) ......................................................................................................... 52 3.2.5 DDVP (Dichlorovos, Nuvan, Vapona, Nogos, Desvap...)................................................... 52 3.2.6 NALED ................................................................................................................................ 53 3.2.7 DIPTEREX (Clorophos, Trichlorfon, Diloc, Tugon, Nevugon...) ...................................... 53 3.2.8 MOCAP (Enthorophos, Ethoprop, Prophos) ....................................................................... 54 3.2.9 METHIDATHION............................................................................................................... 54 3.2.10 BIAN, BI58 (Dimethoate, Phosphamid, Rogor, Phostion, Rostion, Thimetion) .............. 55 3.2.11 PHOSPHAMIDON (Dimecron, Cibac-570, Dixion, OR-1191, Apamidon)..................... 56 3.2.12 AZODRIN (Monocrotophos, Nuvacron, Monocron, Bilobran) ........................................ 57 3.2.13 ZOLONE (Benzophos, Rubitox) ....................................................................................... 57 3.3 THUC TR SU CARBAMATE .................................................................................. 58 3.3.1 SEVIN.................................................................................................................................. 59 3.3.2 MIPCIN................................................................................................................................ 59 3.3.3 BASSA................................................................................................................................. 60 3.3.4 FURADAN .......................................................................................................................... 61 3.3.5 Cc loi thuc Carbamate khc......................................................................................... 61 3.4 THUC TR SU GC PYRETHROIT (GC CC TNG HP)............................... 63 3.4.1 CYPERMETHRIN .............................................................................................................. 63 3.4.2 ALPHA CYPERMETHRIN ................................................................................................ 64 3.4.3 DELTAMETHRIN .............................................................................................................. 65 3.4.4 CYHALOTHRIN................................................................................................................. 65 3.4.5 FENPROPATHRIN............................................................................................................. 66 3.4.6 FENVALERAT ................................................................................................................... 66 3.4.7 PERMETHRIN .................................................................................................................... 67 3.4.8 CC LOI THUC PYRETHROIT KHC...................................................................... 68 3.5 THUC TR SU SINH HC......................................................................................... 68 3.5.1 HORMON (Hc mn) ......................................................................................................... 68 3.5.2 PHEROMON (Cht dn d gii tnh) ................................................................................. 69 3.5.3 MT S CH PHM SINH HC TR SU PH BIN................................................ 69 3.5.4 THUC TR SU VI SINH BACTERIN ......................................................................... 74 3.6 THUC TR NHN ......................................................................................................... 75 3.6.1 ACRINATHRIN .................................................................................................................. 75 3.6.2 AMITRAZ ........................................................................................................................... 76 3.6.3 BINAPACRYL .................................................................................................................... 76 3.6.4 PROPARGITE..................................................................................................................... 77 3.6.5 CC LOI THUC TR NHN KHC ......................................................................... 78 3.7 THUC TR CHUT....................................................................................................... 79 3.7.1 BRODIFACOUM (Klerat, Talon) ....................................................................................... 79

3.7.2 PHOSPHUA KM (Zinc phosphide) .................................................................................. 79 3.7.3 WARFARIN (Coumafne) .................................................................................................. 80 3.7.4 WARFARIN SODIUM + SALMONELLA var. I7F - 4 ..................................................... 80 B. THUC TR BNH CY................................................................................................. 81 3.8 PHN LOI THEO KIU TC NG ........................................................................... 81 3.9 PHN LOI THEO NGUN GC HA HC ............................................................... 81 3.9.1 THUC TR NM CHA NG ................................................................................... 81 3.9.2 THUC TR NM GC LU HUNH.......................................................................... 84 3.9.3 THUC TR NM GC THY NGN .......................................................................... 89 3.9.4 THUC TR NM DICACBOXIN .................................................................................. 89 3.9.5 THUC TR NM HU C NI HP........................................................................... 90 3.9.6 Thuc tr nm tng hp hu c khc .................................................................................. 97 3.10. THUC KHNG SINH .................................................................................................. 99 C. THUC TR C .............................................................................................................. 102 3.11.1 nh ngha........................................................................................................................ 102 3.11.2 c im c di ............................................................................................................... 102 3.11.3 Kh nng cnh tranh vi la ............................................................................................ 102 3.11.4 Phn loi c di................................................................................................................ 102 3.11.5 Thuc tr c ..................................................................................................................... 104 Cu hi n tp ......................................................................................................................... 107 TI LIU THAM KHO ............................................................................................... 108

Gio Trnh Ho Bo V Thc Vt

Chng m u

CHNG M UI. V TR v VAI TR CA MN HC 1. Dch hi v mc tc hiDch hi trong nng nghip (pests): l nhng loi sinh vt v vi sinh vt gy hi cho cy trng v nng sn, lm tht thu nng sut hoc lm gim phm cht nng sn, thc phm. Cc loi dch hi thng thy l su hi, bnh cy, c di, chut, nhn , tuyn trng... Tht thu hng nm do cc loi dch hi gy ra chim khong 35% kh nng sn lng ma mng (khong 75 t la); trong thit hi do su l 13,8% (29,7 t la); do bnh cy l 11,6% (24,8 t la); do c di l 9,5% (20,4 t la) (theo Cramer H. H., 1967). Nu tnh cho din tch nng nghip ca th gii l 1,5 t hcta, khng k ng c v bi hoang th thit hi bnh qun l 47- 60 la trn mt hcta. trnh tht thu, hin nay c nhiu bin php c p dng phng tr cc loi dch hi.

2. Cc bin php bo v thc vtNi chung, trong t nhin c rt nhiu yu t lm hn ch s pht trin ca dch hi. Tuy nhin trong trng trt, phng tr dch hi, tc ng ca con ngi nhm tiu dit hoc ngn nga s pht trin ca cc loi dch hi l rt quan trng v cn thit. t c mc ch trn, con ngi c th dng nhiu bin php, tc nhn c kh nng gy nguy him cho i sng ca dch hi. Cc bin php tc nhn ny thng tiu dit dch hi, hoc ngn nga s ly lan ca chng t vng ny sang vng khc, hoc lm gim mt s ca chng trong mt vng nht nh. Hin nay cc bin php sau y thng c s dng ring r hoc ng thi phng tr dch hi: a. Bin php kim dch thc vt: Nh nc ban hnh cc qui nh, lut l, nhm kim sot v hn ch s ly lan ca dch hi t vng ny sang vng khc, t nc ny sang nc khc. b. Bin php canh tc: Bng cch lm t, bn phn, ti tiu cn i v y , chm sc cy trng ng mc, p dng lun canh hp l, chn thi im gieo trng thch hp... c th lm tng sc chng chu ca cy trng v to iu kin bt li cho s pht trin ca cc loi gy hi, t s hn ch c s pht trin ca cc loi ny. c. Bin php c hc: Nh bt su bng tay, nh c... d. Bin php l hc: Bng cch cy i, phi t, t ng... c th tiu dit c nhiu loi dch hi tr n trong t, trng su, mm bnh, mm c, chut... Ngoi ra ngi ta cn dng by n, nh sng, m thanh kt hp vi cc cht c thu ht v tiu dit cc loi cn trng gy hi. e. Bin php ha: L bin php dng cc ha cht c phng tr dch hi. f. Bin php sinh hc: L bin php s dng cc loi thin ch c ch trong thin nhin. Phng tr tng hp: Ngy nay trn th gii ang pht trin xu hng phng tr dch hi bng cch s dng kt hp mt cch hi ha, hp l nhiu bin php, k c vic pht huy nhng nhn t c sn trong t nhin c kh nng gy bt li cho s pht trin ca dch hi. Trong s cc----------------------------------------------------------------------------------------------------------------------------------------------------PGs. Ts. Trn Vn Hai

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Chng m u

bin php phng tr dch hi k trn, hin nay bin php ha BVTV vn cn chim u th, mc d ngi ta ch ra nhiu nhc im ca vic dng ha cht c trong phng tr dch hi.

3. u im, nhc im v v tr ca ngnh Ha BVTV hin nayu im - Dit dch hi nhanh, c kh nng chn ng c s lan trn ph hoi ca su, bnh v cc sinh vt gy hi khc. c bit l khi xy ra cc trn dch, s dng ha cht phng tr t ra hu hiu. - Cho hiu qu trc tip, r rt, tng i trit , nht l khi dng tr dch hi (su, chut...) trong nh knh, kho cha nng sn, hng ha. - Thng nng cao nng sut, phm cht nng sn mt cch r rt. - D ng dng rng ri nhiu ni, nhiu vng khc nhau. Nhc im - D gy c cho ngi trc tip p dng thuc (pha ch, phun thuc...), cho gia sc, sinh vt c ch chung quanh khu vc p dng thuc. Nu s dng khng ng cch, i khi thuc cn gy c cho thc vt, hoc cn lu b trong nng sn v gy c cho ngi hoc gia sc n phi. - Nhiu trng hp thuc nh hng su sc n qun th sinh vt v cn bng sinh thi, nht l nhng vng m bin php ha BVTV c s dng trn qui m ln. - Gy nhim trn mi trng sng, nht l i vi cc loi thuc c bn ln, d lu tn trong t vi mt thi gian kh di. Phi mt khong 10 nm phn hy 95% DDT, hin nay DDT thy hin din trong t nhiu ni. - Gy ra hin tng qun th dch hi khng thuc, thng xy ra nht l khi dng mt loi thuc lin tc trong nhiu nm ti mt a phng. y l mt vn rt quan trng ang c quan tm, nht l i vi cc loi su, nhn gy hi, do chng rt d hnh thnh tnh khng thuc. Vi nhng nhc im trn, hin nay trn th gii ang c xu hng hn ch s dng cc ha cht c trong BVTV, ng thi c gng tm ra nhng loi thuc mi c nhng u im v trnh c nhng nhc im k trn. Ni chung vi nhng u im m cc bin php khc cha c c, p ng c yu cu ca sn xut, bin php ha BVTV hin nay vn cn c s dng rng ri. Nhu cu v ha cht BVTV trn th gii ngy cng tng, lng thuc tiu th tnh thnh tin trong nhng nm gn y l: + 1986: 14.400 triu la M + 1987: 20.000 triu la M + 1990: 21.800 triu la M

II. Lch s php trin ngnh Ha BVTVC th chia lm ba giai on nh sau:----------------------------------------------------------------------------------------------------------------------------------------------------PGs. Ts. Trn Vn Hai

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Chng m u

- T th k XVIII tr v trc: Cng tc BVTV ni chung v bin php Ha BVTV ni ring ch c tin hnh l t, t pht, cha c c s khoa hc v khng c ngha thc tin. Ch yu con ngi s dng nhng cht c c sn trong t nhin nh lu hunh c trong tro ni la, cy c c cha cht c... phng tr dch hi. - T th k XVIII n trc nm 1939: khi sn xut nng nghip mang tnh cht tp trung hn th thng xy ra cc trn dch su bnh, i khi lan trn t nc ny sang nc khc, cho nn i hi v cng tc BVTV tr nn cp bch hn. Nh cc khoa hc v cn trng, bnh cy v nhng ngnh khoa hc t nhin c lin quan khc bc vo giai on hin i, cc bin php phng tr dch hi khoa hc, tin b mi dn dn c p dng vo sn xut nng nghip. Nm 1807, Benedict Prevot chng minh c rng nu nc si trong ni ng c tnh c i vi bao t nm bnh than en, tip sau , Millardet nghin cu s hn hp gia ng sulphate v vi to ra hn hp Bordeaux phng tr bnh sng mai trn nho (1882 1887). Nm 1889, Aceto asenate ng- hp cht cha Asen khng tan u tin c dng phng tr su Leptinotasa decemlineata Say hi khoai ty nhiu nc Chu u. Nm 1897 Rabate s dng H2SO4 v Martin dng st sunfate tr c cho ng cc.... Nhn chung t gia th k XIX tr i, bin php Ha BVTV ngy cng c ch trng v bc u pht huy c tc dng trong sn xut. Tuy nhin vn cn nhiu hn ch do nhng hp cht ha hc dng trong giai on ny - ch yu l cc cht v c - cn mang nhiu nhc im: d gy c cho ngi v gia sc, km an ton i vi cy trng. - T nm 1939 n nay: T khi ng Muller cng b cng trnh nghin cu ca ng v thuc tr su DDT th bin php ha hc phng tr su hi c mt chuyn bin cn bn. Sau hng lot cc hp cht Clo hu c v cc hp cht tng hp hu c khc (ln hu c, Cc-bamat, Pyrethroid tng hp...) ra i v c s dng ngy cng rng ri phng tr su hi. i vi nm bnh, bt u bng cc thuc tr nm cha ng, ngy nay ngi ta dng nhiu hp cht hu c tng hp nh cc thiocarbamate, cc hp cht thy ngn hu c, cc hp cht benzimidazol, cc thuc khng sinh... phng tr nm v vi khun. n nm 1945, khi nhng thuc tr c Phenoxy (2,4-D, MCPA...) ra i th bin php ha hc phng tr c di mi tht s c ngha trong sn xut nng nghip. Trong nhng nm gn y, bin php Ha BVTV c nhng bc tin mnh m, xut hin nhiu loi nng dc vi bn cht ha hc hon ton mi, c nhiu u im so vi cc hp cht so vi cc hp cht dng trc y nh: an ton hn vi ngi v ng vt mu nng, cy trng, dit c nhng loi dch hi khng vi cc loi thuc s dng trc y...

III. C s mc ch v i tng mn hcC s khoa hc ca bin php Ha hc BVTV l c cht hc nng nghip. + c cht hc: (Toxicology) l mn khoa hc chuyn nghin cu cc cht c v tc ng ca chng n c th sng; cch phng v chng tc dng c hi ca chng. + c cht hc nng nghip: l mt ngnh ca c cht hc, chuyn nghin cu cc cht c dng trong nng nghip nhng cht tr dch hi; tm hiu nhng bin i xy ra trong c th sinh vt di tc ng ca cc cht c ; tm hiu s pht sinh, pht trin ca nhng bin i trong c th sinh vt. Nh vy i tng ca c cht hc nng nghip l thuc tr dch hi v c ch ca s tc ng .----------------------------------------------------------------------------------------------------------------------------------------------------PGs. Ts. Trn Vn Hai

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Chng m u

+ Tnh c ca mt cht c i vi sinh vt ph thuc vo 3 yu t sau: c im ca cht c (tnh cht ha hc, tnh cht vt l, kh nng tc ng sinh l, liu lng...). c im ca sinh vt b thuc tc ng: cc c im di truyn nh cu to hnh thi gii phu, h thng men, hot tnh sinh l v cc c im khc nh th trng, tui tc, tnh trng sc kho... iu kin ngoi cnh khi cht c tc ng ln c th dch hi, cc yu t thng gy nh hng l nhit , m , gi, ma... cc yu t ny mt mt tc ng ln dch hi lm nh hng n tnh mm cm ca n; mt khc nh hng n tnh cht l, ha hc ca thuc, t lm tng hay gim hiu qu dng thuc.

Mc ch ca ngnh c cht hc nng nghip l nghin cu s tc ng ca thuc ln c th sinh vt trong mi quan h gia 3 yu t nu trn t : + ra nhng yu cu ca sn xut nng nghip i vi mt loi thuc tr dch hi m ngnh ha hc cn gii quyt. + ra cc bin php dng thuc hp l nht, nhm pht huy n mc ti a hiu lc tr dch hi v hn ch n mc ti thiu tc hi ca thuc trn ngi, gia sc, cy trng, mi trng v cn bng sinh thi.

Cu hi n tpCu 1: Hy cho bit v tr v vai tr ca ngnh Ha Bo V Thc Vt trong nng nghip? Cu 2: Hy cho bit u v khuyt im ca ngnh Ha Bo V Thc Vt trong nng nghip?

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Chng 1

CHNG 1: C CHT HC NNG NGHIP1.1 CC KHI NIM V CHT C v S NHIM C 1.1.1 Cc khi nim c bna. c cht hc (Toxicology) L mn khoa hc nghin cu v cht c v s tc dng ca n ln c th sng, cch phng v chng tc dng c hi ca chng. c cht hc nng nghip l mt ngnh ca mn c cht hc, chuyn nghin cu cc cht c dng trong nng nghip, cc thuc tr dch hi; v tm hiu nhng bin i c th xy ra trong c th sinh vt di tc ng ca cht c khc nhau. b. Cht c (Toxicant) * Cht c: l mt cht khi xm nhp vo c th vi mt lng nh cng c th gy ng c, ph hy vi chc nng ca c th hay gy t vong cho c th . * Tnh c (Toxicity) ca cht c: l kh nng gy c cho c th ca cht trong nhng iu kin nht nh, tnh c ca mt cht ph thuc vo cc yu t sau: - Tnh c ph thuc vo bn cht ca cht c (c im ha hc, l ha, sinh vt hc... ca cht c). - Tnh c biu hin tu theo i tng tc ng, cht c c th gy ng c c hay khng cn tu thuc vo c im ca c th sinh vt b tc ng. Mt cht c th c vi sinh vt ny m khng c vi sinh vt khc. Ansen v stricnin l nhng cht c c dng lm thuc tr chut, nhng cng c ng dng trong y hc lm thuc cha bnh cho ngi. - Cht c ch c kh nng gy c mt liu lng nht nh no (t liu lng ngng tr ln). Khi lng cht c trong c th sng di mt lng no n s khng c kh nng gy c na. - Tnh c ca mt cht cn tu thuc vo iu kin v phng php p dng. S c mt ca axit HCL trong dch v l mt iu bnh thng nhng nu tim axit ny vo mu th li gy ng c. - Thc o c ca thuc c i vi mi c th sng l liu lng c (Toxic dose). c. Liu lng c (Toxic dose) L lng cht c cn c gy c mt tc ng nht nh trn c th sinh vt. Liu lng c c th tnh bng g hay mg cht c trn mt c th. Tuy nhin, do c s sai khc v ln ca c th cng nh s sai khc v mn cm ca c th cho nn din t mt cch chnh xc hn, c ca mt cht thng c tnh bng lng cht c cn gy c cho mt n v th trng (n v l g/kg, mg/kg hay g/kg th trng). Liu lng c cng nh th tnh c ca cht c cng ln. Liu lng c c th c phn bit thnh cc mc nh sau: * Liu lng gy cht trung bnh(LD50): l liu cht c trong nhng iu kin nht nh gy cht cho 50% c th dng trong nghin cu. * Liu lng ngng: l liu cht c ti thiu trong nhng iu kin no , c th gy ra nhng bin i khng ng k cho c th nhng cha gy hi n sc khe mt cch r rng c th cm thy c.----------------------------------------------------------------------------------------------------------------------------------------------------PGs. Ts. Trn Vn Hai

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Chng 1

* Liu lng c: L liu cht c lm cho c th lm vo tnh trng xu nh gy ht hi, chng mt, nhc u... nhng cha a n t vong. * Liu lng gy cht: l liu cht c nh nht c th gy cho c th nhng bin i khng th hi phc c, dn n t vong. Ngoi ra ngi ta cn a ra mt s khi nim khc v liu lng c nh sau: * Liu lng di liu gy cht: L liu cht c c th gy ra s hy hoi vi chc nng ca c th nhng cha dn n t vong. * Liu lng gy cht ti thiu: l liu cht c nh nht trong nhng iu kin nht nh c th gy cht cho c th. * Liu lng gy cht tuyt i: L liu cht c thp nht trong nhng iu kin nht nh c th lm cht ton b s c th dng trong nghin cu. d. Mc dng (liu dng, liu lng p dng) L lng hot cht hoc ch phm ca n dng trn mt n v th tch, din tch hoc khi lng cn x l bo v cy trng v nng sn, nhm thu c hiu qu k thut v hiu qu kinh t cao nht. Mc dng c tnh bng n v trng lng ca vt cht hoc ch phm trn mt n v trng lng, th tch hoc din tch ca i tng cn x l. n v mc thng dng l kg(lt) hot cht/ha. i khi ngi ta ch khuyn co nng s dng cng vi yu cu l thuc phi c phun u khp b mt cn x l.

1.1.2 Nhng yu cu i vi mt ha cht dng trong bo v thc vta. Hp cht dng trong bo v thc vt phi c tnh c cao i vi sinh vt gy hi, c kh nng tiu dit hoc ngn chn s ph hoi ca mt hay nhiu loi dch hi. y l iu kin tin quyt v nu mt i tnh cht ny th vic dng ha cht BVTV chng c ngha g c. b. An ton i vi cy trng, vi ht ging v khng nh hng xu n phm cht nng sn liu lng, nng v phng php s dng qui nh. c. An ton i vi ngi s dng thuc (ngi pha ch thuc, phun thuc...).Vi ngi v gia sc tiu th nhng sn phm thu hoch t cy trng c phun thuc. Nhng thuc ny phi c c cp tnh i vi ng vt mu nng thp; khng tch ly trong c th ng vt; khng phi l tc nhn gy ung th, qui thai v cc bnh mn tnh him ngho khc. d. Hp cht ny phi c tnh chn lc cao, khi s dng trn ng rung chng phi t hoc khng nh hng xu n s pht trin ca nhng sinh vt c ch nh cn trng bt mi v k sinh, ong mt, c, cua... e. Khng gy nhim mi trng sinh sng. Cc hp cht ny khng phi qu bn vng trong iu kin s dng; khng tn ti qu lu trong cy trng v nng sn, trong t, ao, h, sng, sui, nc ngm...Sau khi c phun, ri trn ng rung, trong mt thi gian ngn, thuc phi dit c nhng sinh vt gy hi v sau phi phn gii thnh nhng cht khng c cho ngi v ng vt. f. Cc ch phm dng trong BVTV phi khng i hi cch s dng, bo qun v chuyn ch qu phc tp, v iu ny khng ph hp vi trnh k thut v c s vt cht nng thn, nht l i vi nng thn nc ta.----------------------------------------------------------------------------------------------------------------------------------------------------PGs. Ts. Trn Vn Hai

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g. Cc ch phm phi khng c qu t tin, phi em li hiu qu kinh t cao khi s dng chng. Ngy nay cng nghip ha cht v ang c nhiu n lc ch to ra nhng hp cht p ng ngy cng tt hn nhng yu cu ni trn. Tuy nhin cn phi thy rng cha c ha cht no p ng tht y tt c nhng yu cu trn. Vi k thut dng thuc ng n, trn c s hiu bit tht y v c cht hc nng nghip s gp phn khc phc nhng mt hn ch v nng cao gi tr s dng ca cc ha cht c trong lnh vc phng tr dch hi. Nu chng ta coi thuc BVTV nh mt v kh chng li nhng sinh vt gy hi cho cy trng th kt qu thng li hay tht bi ca trn nh u phi ch ph thuc vo v kh? R rng ngi s dng v kh ng vai tr quyt nh.

1.1.3 Phn loi thuc tr dch hiC nhiu cch phn loi thuc tr dch hi, sau y l mt s cch phn loi thng dng nht: a. Phn loi theo ngun gc v thnh phn ha hc Thuc tr dch hi c chia thnh cc nhm sau: - Cc thuc c ngun gc thc vt: Cc b phn ca mt s thc vt c cha cc hp cht alcaloid, nicotin, albazin, pyrethrin, rotenone, v mt s cht khng sinh c s ch hoc trch ly hot cht s dng. - Cc thuc v c: Gm cc hp cht v c cha ng, lu hunh, cc hp cht asenit... - Cc thuc tng hp hu c: Gm cc hp cht thuc nhm chlor hu c, nhm ln hu c, nhm carbamate, nhm cc hp cht d vng, nhm pyrethroid tng hp... Cc li thuc c ngun gc vi sinh vt: Cc thuc khng sinh. b. Phn loi theo i tng tc dng Cc thuc tr dch hi (pesticide) c chia thnh: Thuc tr su (insecticide), thuc tr bnh (fungicide), thuc tr vi khun (bactericide), thuc tr c di (herbicide), thuc tr chut (ratticide), thuc tr tuyn trng (nematocide), thuc tr nhn (acaricide), thuc tr c sn (limacide, molluscide), thuc git ng vt (zoocide). Trong mt s trng hp, thuc tr dch hi cn c chia thnh tng nhm da vo kh nng gy c ca thuc n mt giai on sinh trng nht nh ca ch hi: Thuc tr su non (larvicide), thuc tr trng (ovicide)... c. Phn loi theo phng php thm thu v c tnh tc dng Tu theo con dng m cc cht c xm nhp vo c th dch hi, c th phn cc loi thuc tr dch hi theo cc nhm sau: - Thuc v c (thuc ni tc ng): L nhng thuc xm nhp vo c th cng vi thc n qua con ng tiu ha, thng dng dit cc cn trng nhai gm, lim ht, chut... - Thuc tip xc: Xm nhp vo c th qua da, biu b, thng dng dit cc cn trng sng khng n nu, cc vi sinh vt gy hi, tr c... - Thuc xng hi: Qua dng hi thuc khuych tn vo khng kh chung quanh dch hi v xm nhp vo c th qua ng h hp. Ngoi ra ngi ta cn phn bit:

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- Thuc lu dn v thuc khng lu dn: Thuc lu dn l nhng thuc khi c p dng trn b phn ca thc vt (nh l hoc r) th n c kh nng xm nhp vo bn trong v dn truyn theo mch nha n cc b phn khc lm cho c th thc vt tr nn c i vi dch hi (thuc tr su, bnh); hoc ton b c th thc vt b gy hi (thuc tr c). Thuc khng lu dn l tt c nhng thuc khng c c tnh trn, cc thuc c c tnh lu dn thng c a chung hn do t b ma ra tri, t gy hi n thin ch. - Thuc c tc ng chn lc v khng chn lc: Thuc c tc ng chn lc l nhng thuc ch c tc dng trn mt s loi dch hi v khng nh hng xu n cc loi thin ch (cn trng bt mi v k sinh) hay nhng sinh vt c ch khc (gia sc, c, th, thin ch (cn trng k sinh) hay nhng sinh vt c ch khc (gia sc, c, th rng...). i vi thuc tr c, tnh chn lc ca thuc biu hin kh nng khng gy hi i vi thc vt. Thuc Bo V Thc Vt dng trong nng nghip cn c phn nhm theo cc ch tiu c hi i vi ngi v ng vt mu nng, cng nh theo tnh bn vng ca chng trong mi sinh. c tnh ca thuc i vi VMN c tnh qua mt ln a thuc qua d dy (qua ming), bi thuc ln da (tip xc qua da) v khi ht hi thuc, v s tch ly ca thuc trong c th ng vt. (Trch theo Kinh t v t chc Bo V Thc Vt; trang 205 phn Phn loi v sinh thuc Bo v Thc vt. A.F. Chenkin, theo Vin Nghin cu Khoa hc Ton Lin Bang v V Sinh v c hi ca Thuc BVTV), NXB Nng nghip - H Ni, 1988. d. Phn loi theo mc bay hi - Cht rt nguy him: Nng bo ha nng c hi. - Cht nguy him: Nng bo ha > nng bc chy. - Cht t nguy him: Nng bo ha < nng bc chy. e. Phn loi theo c s y hc *Theo c cp tnh qua da: LD50 (mg/kg) < 300 300< LD50 3 Mc c (c tnh) c tnh mnh c tnh trung bnh c tnh yu

*Theo c cp tnh qua ming hay ng rut (biu th bng LD50, th nghim trn chut), cc loi thuc tr dch hi c chia thnh cc nhm nh sau: Bng phn chia nhm c qua ming theo qui nh ca B Nng Nghip & PTNT v Cng Ngh Thc Phm, 1995. Phn nhm v k hiu nhm c I Rt c ch en trn bng mu II c cao Biu tng nhm c u lu xng cho c cp tnh LD50 (mg/kg)qua ming

Th rn 2000

f. Phn loi theo dng tch ly Thuc tr dch hi c kh nng tch ly trong c th sinh vt di cc dng sau: +Tch ly ha hc: xy ra khi cht c ha hc c hp thu vo c th vi tc nhanh hn l bi tit ra ngoi. Mi ln cht c ha hc xm nhp vo c th u khng thi ra ngoi hon ton, s tch t ca cht c xy ra khin c th dn dn b ng c v cht. + Tch ly ng thi (tch ly chc nng): mi ln cht c xm nhp vo c th u b thi ra hon ton, tuy nhin hu qu ca s tc ng ca liu cht c vn cn v c tng thm do qua cc ln xm nhp sau. Kh nng tch ly trong c th ca mt cht c biu th qua cc h s tch ly: LD50 (MN TNH) H s tch ly K = ....................................... LD50 (CP TNH) K 5 :

Ngoi ra y hc cn da vo mc to khi u ngi v ng vt, phn loi cc cht c theo mc gy c theo mc gy t bin gen, gy qui thai... g. Phn loi theo kh nng phn hy Da vo chu k bn hy (DT50: Disappearance Time) ca ha cht l thi gian phn hy phn na lng cht c. - DT50 < 1 thng - DT50 = 1- 6 thng : bn vng thp : bn vng trung bnh.

- DT50 = 6 thng - 1 nm : bn vng cao. - DT50 > 1 nm : bn vng rt cao.

1.2 S XM NHP CA CHT C VO C TH SINH VTCht c xm nhp vo c th theo nhng con ng khc nhau: qua ng tiu ha (thuc v c), qua ng h hp (thuc xng hi), qua da hay biu b (thuc tip xc). Cho d----------------------------------------------------------------------------------------------------------------------------------------------------PGs. Ts. Trn Vn Hai

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xm nhp vo c th bng con ng no i na, cc cht c mun gy ra mt tc ng no ln c th sinh vt u phi xm nhp c vo bn trong t bo ca sinh vt .

1.2.1 S xm nhp ca cht c vo t boa. S lc v cu to t bo T bo trng thnh in hnh cu to c bn gm c: mng nguyn sinh, nguyn sinh cht, nhn, b my golghi, ty th v cc vi th khc. Ring i vi t bo thc vt v mt s vi sinh vt, bn ngoi mng nguyn sinh cn c mng t bo - l mt mng cellulose cng bo m cho t bo c bn vng. b. S xm nhp ca cc cht vo bn trong ca t bo Mng t bo c kh nng thm thu rt ln i vi cc cht khong v cc cht hu c. Thng qu trnh hp thu cc cht i qua mng ny xy ra nh vo s hp thu phn t, s trao i ion hoc lin kt ha hc. Mng nguyn sinh cht c cu to chuyn ha rt phc tp v l vt cng th hai trn con ng cc cht thm nhp vo c th do cc yu t sau: Tnh thm chn lc: cc cht i qua mng t bo vi tc khc nhau, iu ny lm cn tr kh nng khuych tn ca nhiu cht vo t bo. Tuy nhin tnh thm ny c th thay i khi c t bo b mt tc ng no . Nh khi chu s tc ng ca tc nhn gy hi, t bo c th b kch thch hoc b tn thng v khi tnh thm ca mng t bo tng ln r rt, lc cc cht - k c cht c s khuych tn nhanh chng v bn trong t bo cho n khi cn bng v p sut c xc lp Kh nng hp thu ca ton khi nguyn sinh cht: kh nng ny c c trng bi mt h s no . Khi b cht c tc ng th h s ny tng ln do tnh hp thu ca khi nguyn sinh cht tng ln, kt qu l cht c xm nhp vo t bo vi mt tc nhanh hn. Kh nng hp ph ca mng nguyn sinh cht: c bit l i vi cc kim loi nng nh Hg, Cu, As... Cc cht c ny thng phn ng vi cc nhm thio v amin ca mng t bo, trong nhiu trng chng ph hy mng t bo i vo bn trong. Nhn chung cc cht hu c thng xm nhp vo t bo bng con ng khuych tn di dng phn t qua cc khe lipoprotein ca mng t bo. Cc cht c v c nh cc hp cht ca Cu, Fe, Zn... thng xm nhp vo t bo di dng ion hoc phn t.

1.2.2 S xm nhp ca cht c vo c th cn trngCc thc tr su xm nhp vo c th cn trng theo 3 con ng: qua b my tiu ha (thuc v c); qua biu b (thuc tip xc) v qua con ng h hp (thuc xng hi). Vi tng cch xm nhp, cht c s b chuyn ha theo nhng hng khc nhau v gy ra nhng tc ng khc nhau. a. Tc ng v c - S hp thu cht c: Cc thuc v c cng vi thc n i vo c th cn trng. T lc bt u vo ming, i qua ng thc qun, cho n khi vo ti thc n, cht c c chuyn ha----------------------------------------------------------------------------------------------------------------------------------------------------PGs. Ts. Trn Vn Hai

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t dng khng ha tan sang dng ha tan. Khi n rut gia, qu trnh ng ha cht c xy ra mnh m. Bng cch thm thu hoc ph hyvch rut gia, cht c t rut chuyn vo huyt dch. Cng vi huyt dch, cht c vn chuyn i khp c th, xm nhp v tc ng vo cc trung tm sng quan trng (nh h thn kinh, h men), hoc gi trong cc m (nh m m). - S bi tit cht c: trong qu trnh tiu ha thng khng phi ton b s lng cht c u c c th hp thu v ng ha. Mt phn cht c khng kp hoc khng c chuyn ha thnh trng thi ha tan s b thi ra ngoi bng con ng bi tit qua rut sau v l hu mn. Nh vy i qua rut vi tc cng nhanh, cht c b bi tit i ra ngoi cng nhiu, v do cng t tc ng n c th dch hi. Mt s cht nh Asen gy ra s co bp rut gia khin cho cht c mt phn b tng ra khi c th cn trng. b. Tc ng tip xc - Biu b cn trng c cu to ch yu bi 3 lp: biu b trn, biu b ngoi v biu b trong. Lp biu b trn ngoi cng c dy khong 0,2 - 0,8 cu to t mt hn hp acid bo, cholesterin v protein. Biu b, ch yu l lp biu b trn l vt chng ngi quan trng nht trn con ng xm nhp ca nhng cht khng tan trong sp v lipit. Thng biu b chn v m chn ca cn trng tng i mng nn cht c xm nhp qua nhng ni ny tng i d dng. mt s cn trng, biu b cn c bao bc bi mt lp sp bn ngoi (nh rp sp). - Thng thng ch c nhng cht hu c ha tan c trong lipoit v lipoprotein mi xm nhp c qua biu b. Sau khi qua c bu b, cht c s lan vo huyt dch v truyn i khp c v tc ng nh trong trng hp cc cht v c. - Mt s thuc tr su nht l cc loi du, tinh du c th to thnh mt lp mng bn vng bao ph c th cn trng lm cn tr qu trnh h hp ca chng, v do cc cht ny c th git cn trng ngay c khi cha xm nhp c vo c th. V d nh du khong DC Trons Plus do hng Caltex sn xut, du khong SK do Hn quc sn xut. c. Tc ng xng hi Bng dng hi, cht c xm nhp vo c th cn trng qua h thng kh qun. Chng khuych tn qua vch kh qun v vi kh qun vo huyt dch, lan truyn trong thn v gy ng c cho cn trng. Khi tip xc vi cc cht c xng hi, cn trng thng phn ng t v bng cch ng cc l th li. Nh c lng oxy cha trong kh qun, chng c th chu ng c mt thi gian nht nh. Cho n khi ht lng oxy d tr, chng mi buc phi m cc l th ra; do tiu dit c dch hi, ta phi gi cho khng kh chung quanh dch hi lun cha kh c nng gy cht trong mt thi gian tng i di th mi c hiu qu. Chnh v vy m cht c xng hi ch pht huy tc dng khi c p dng nhng ni c khong khng gian c nh nh kho, khoang tu, nh knh...

1.2.3 S xm nhp ca cht c v c th loi gm nhmThng l ch ng dng nhng cht v c hoc xng hi tiu dit nhng loi gm nhm. - Cht v c sau khi i vo b my tiu ha cc loi gm nhm c ng ha d dy. Sau cht c nguyn cht hoc cc sn phm chuyn ha ca n thm qua vch rut vo mu----------------------------------------------------------------------------------------------------------------------------------------------------PGs. Ts. Trn Vn Hai

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v c mu truyn i khp ni trong c th. Cc loi gm nhm c khu gic v v gic rt pht trin li rt a nghi nn chng c th phn ng t v bng cch ln trnh, khng n b c hoc bng cch nn ma b c ra ngoi. - Cht c xng hi xm nhp d dng vo phi ca loi gm nhm v t c mu vn chuyn i khp c th. Ngoi kh nng theo huyt dch n cc c quan khc v gy tc ng, cht c xng hi cn c kh nng tc ng ln chnh huyt dch, lm mt kh nng vn chuyn kh oxy, kh carbonic v cc cht khc lm nh hng n ton b c th.

1.3.2 S bin i ca cht c trong t bo sinh vta. Bin i ha hc Cht c phn ng vi cc thnh phn ca t bo ch yu l vi cc protein hoc vi cc thnh phn kim loi trong cc hp cht protit. V d nh: formaldehyd khi xm nhp vo t bo s tc dng vi cc amino acid to thnh cc methylamin. b. Bin i sinh hc - Cht c c th c ch hot ng ca cc enzym nh nhng enzym esteraza (cholin esteraza, methyl butyrat esteraza, phenyl acetat esteraza...) v nhiu enzym khc trong t bo, lm nh tr cc hot ng ng ha v d ha ca t bo, thuc tr c Natrichlorate c ch hot ng ca enzym catalaza trong c, cc thuc tr su ln hu c c kh nng c ch hot ng ca men cholinesterase (ChE.) v mt s men khc m cc men ny dng thy phn Acetylcholin. Acetylcholin c trong t bo thn kinh v tham gia vo qu trnh truyn xung ng thn kinh. V th khi cholin-estaza b c ch, acetylcholin b tch ly lm ri lon s dn truyn xung ng thn kinh, nhng cht gi l thuc c thn kinh. C loi cht c tc ng bng cch ngn cn s to thnh vitamin trong t bo hoc lm mt tc dng ca vitamin ny i vi t bo. Cc dn xut ca hydroxicumarin c kh nng c ch s to thnh vitamin K rut cc loi chut, gp phn gy bnh mu khng ng chut. - Tt c cc enzym u l hp cht cha protein, tu theo cu to ca n, ngi ta chia lm hai loi: Loi th nht trong thnh phn ch cha protein; loi th hai ngoi protein cn c thnh phn khc nh kim loi. Cc hp cht c th kt hp vi thnh phn protein hoc thnh phn kim loi lm cho enzym b bt hot hoc b ph hy hon ton. Enzym b bt hot i khi c th c phc hi khi ta tch cht c ra khi t bo. - Cc enzym c bit rt d mn cm vi cht c. Do cc enzym gi vai tr xc tc cho qu trnh sinh hc trong t bo. S ng c ca bt k enzym no u lm cho c th suy yu, thm ch b cht. Khi c mt enzym no trong c th b c ch, ta ni c th b tn thng sinh ha. - Tt c nhng cht c ch enzym, trong c thuc tr dch hi c chia thnh hai nhm: + Nhm c kh nng c ch ton phn: Thng l cc mui ca cc kim loi nng (Pb, Hg), lm lng, kt ta protein dn n c ch hon s hot ng ca cc enzym. + Nhm c kh nng c ch chuyn bit: Thuc c ch lin kt vi mt v tr no trong phn t protein (nh phn kim loi) to thnh nhng lin kt bn vng v c ch hot ng ca enzym. Nh H2S c th lin kt vi phn t st trong enzym ca t bo h hp lm c ch qu trnh h hp.----------------------------------------------------------------------------------------------------------------------------------------------------PGs. Ts. Trn Vn Hai

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c. Bin i l hc Mi loi cht c u c kiu tc ng c trng i vi t bo do cc cht c bn cht khc nhau s tc ng ln nhng thnh phn khc nhau ca t bo, nhng nhn chung tt c nhng tc ng ny u dn n s bin i trng thi keo, nht v kh nng nhum mu ca nguyn sinh cht. S thay i trng thi keo biu hin bng s kt t cc phn t keo trong t bo to thnh nhng phn t ln hn, km theo l phn tn b gim st v c xy ra s kh nc khin cho i lc ca cc phn t nc b gim. Cng vi s kt ng nguyn sinh cht, thng din ra s to thnh nhiu khng bo, chng t s thay i quan h gia cc phn t keo ca t bo i vi nc. Do s kt t keo, nht ca cht nguyn sinh lc u b gim i; nhng sau li tng ln, c th l do s gel ca keo nguyn sinh, hoc do s thay i v hnh dng phn t. Trong t bo bnh thng, cc cht nhum mu nh xanh methylen, trung tnh... khng nhum mu nguyn sinh cht v nhn m thng kt ng li thnh nhng ht nh hoc lin kt vi mt vi thnh phn ca t bo (i vi t bo ng vt). Lc t bo b tn thng, cc cht ny nhm mu u c nguyn sinh cht v nhn. Vi nhng bin i l ha hc ni trn, t bo khng hon thnh c chc nng sinh l bnh thng ca mnh na v c th cht. Ngoi biu hin ph hy t bo, c khi ngi ta cn quan st thy nhng biu hin kch thch ca ha cht c i vi t bo. Naxonop v Alexendrop a ra thuyt bin cht gii thch hin tng ny. Thuyt ny da trn c s l cc protein nguyn th, thnh phn quan trng v ph bin nht trong nguyn sinh cht, c tnh khng n nh v rt nhy cm vi tc ng ca nhiu tc nhn khc nhau. Phn ng thng dn n s bin i cu hnh bnh thng ca protid. Khi ch c mt lng nh cht c tc ng n t bo th cht c mi ch tc ng n mt s thnh phn ca nguyn sinh cht v c th thc y cc phn ng trong t bo xy ra nhanh hn lm tng cng s trao i cht trong t bo. Nhng khi lng cht c tng ln th s bin cht s xy ra su sc v bao trm ln ton khi nguyn sinh cht, lm cho t bo b tn thng. Trng thi tn thng ny lc u c tnh thun nghch, ngha l nu tch t bo ra khi tc ng ca cht c th cht nguyn sinh c th phc hi li trng thi bnh thng. Trng thi ny gi l trng thi cht hoi gi (paranecrosis). Nu b tn thng mc su sc hn, s bin cht khng cn mang tnh cht thun nghch na, m chuyn sang trng thi cht hoi tht (necrosis). Nh vy vi cng mt cht, nu cht c xm nhp vo t bo ch vi mt lng nh th c th gy kch thch, thng vi lng ln th li gy ng c cho c th.

1.3.3 Cc hnh thc tc ng ca cht cC nhiu hnh thc tc ng khc nhau, tu theo c tnh ca tng loi cht c, c im ca i tng v iu kin p dng. a. Tc ng cc b v tc ng ton b + Tc ng cc b (tc ng tip xc): Cht c ch gy tn thng nhng b phn ca c th tip xc vi n m thi. + Tc ng ton b (tc ng lu dn): Cht c c tnh hp thu, c kh nng xm nhp v lan truyn i khp c th, lm nh hng n nhiu c quan hoc c khi nh hng n ton b c th. b. Tc ng tch ly Cht c xm nhp vo c th xy ra s tch ly ha hc hoc tch ly ng thi (xem 3.e).

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c. Trng c cp tnh v mn tnh - Trng c cp tnh (Acute toxicity): Thng xy ra khi cht c thm nhp vo c th ngay mt ln vi lng ln, ph hy mnh m cc chc nng ca c th, biu hin bng nhng triu chng rt r rng, c trng cho mi loi hay mi nhm ha hc. Thuc tr su gc ln hu c th hin r nht. - Trng c mn tnh (Chronic toxicity): Xy ra khi cht c xm nhp vo c th vi lng nh, trong nhiu ln v trong mt thi gian di. Cc cht c kh nng tch ly trong c th nh nhng thuc tr su Clo hu c thng gy ng c mn tnh. Tuy nhin cng c nhng trng hp cht c khng c c tnh tch ly vn c kh nng gy c mn tnh. d. Tnh c d hu Mt s cht c khi xm nhp vo c th th khng gy cht cho c th m ch ph hoi nhng chc nng sinh l ca cc c quan ring bit, lm cho chng khng pht trin bnh thng c na, v sau ny gy thoi ha hoc c khi gy cht cho th h con ci.

1.3.4 Tc ng ca cht c n dch hia. Tc ng ca cht c n c th cn trng v ng vt gy hi Mi loi hoc mi nhm cht c c th gy cho cn trng nhng phn ng c trng, nhng triu chng trng c c bit. Khi tc ng n h thn kinh, cc b phn ca cn trng thng khng c kh nng c ng nhp nhng, n khp vi nhau. Lc u cht c c th gy hng phn cho cn trng ri sau lm cho c th b t lit dn. Cc cht c tip xc c th gy ra cht bng trn da, biu b, hoc lm bin i mu sc da. Khi n phi nhng cht c v c nh hp cht Asen, cn trng c th nn ma, tiu chy. Cc cht c v c c th lm thnh ng tiu ha b tn thng, ng tiu ha b nht mu, rut b nhn nheo, p sut rut cng c th b bin i. Trong c th, cht c c huyt dch dn i khp ni; ngoi ra chnh cc men nm trong huyt dch cng b tc ng lm bin i thnh phn ha hc v hnh thi hc ca huyt dch. Di tc ng ca cht c, c trng hp m thn kinh ca cn trng b phn hy, cc m tuyn b cht... i vi nhng loi gm nhm, cht c cng gy ra bin i bnh l cc c quan ring bit: h thn kinh, h tiu ha, h tun hon, h h hp. Khi cht c tc ng ln h thn kinh, nhng ng ny cng c nhng biu hin co rt, hng phn, t lit. Trong nhiu trng hp cht c lin kt vi hemoglobin trong mu, nh hng n h hp, khin cho chng b cht v ngt th. b. Tc ng ca cht c n tc nhn gy bnh Trong t bo nm, vi khun gy bnh, cht c c th gy ra nhng tc ng sau: - Ph hy cc thnh phn cu trc ca t bo: Cht c c th tc ng trc tip, ph hy mt hoc nhiu thnh phn trong t bo nm bnh (vch t bo, mng t bo, ty th, vi th hoc nhn). Trong t bo nm bnh, do mi cu t c mt chc nng nht nh c lin quan n s hot ng sinh l bnh thng ca ton b t bo nn khi mt cu t no b hy hoi n mt mc nht nh th hot ng sinh l ca t bo b ri lon v cui cng lm cho c th b cht. - Ngn cn s tng hp cc cu t ca t bo: Tc ng ny thc s thng qua s c ch hot ng ca cc men iu khin qu trnh tng hp hoc ngn cn ngay s tng hp men.----------------------------------------------------------------------------------------------------------------------------------------------------PGs. Ts. Trn Vn Hai

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- Tc ng n h sn sinh nng lng ca t bo hoc lm cho nng lng d tr b phng thch ba bi. Cht c c th gy cht cho t bo vi sinh vt (fungicide - cht dit nm, batericide - cht dit vi khun), nhng cng khi ch lm ngng tr s sinh trng v sinh sn ca t bo, nhng cht ny gi l cht nm tnh ha (fungistate - cht nh ch hot ng ca nm), vi khun tnh ha (bacteriostate - cht nh ch hot ng ca vi khun), dc tnh ha (genostat, cht ngn cn s to thnh bo t). Tuy nhin ngi vn gi chung nhng cht ny l thuc tr nm. c. Tc ng ca cht c n c di Nhiu loi thuc tr c gy ra cho c di nhng triu chng rt in hnh. Nhng triu chng thng thy l: l c b trng ra tng mng hoc c nhng m b chy; l c th b xon, ho vng ton b ri li, rng i. Nhng thuc tr c phenoxy lm cho ngn b xon, l mc d dng, thn cong v c nhiu r trn thn... Cc cht c c nhng tc ng rt khc nhau n hot ng sng ca c di: gy ri lon sinh trng, ngn cn s phn chia t bo, ph hy dip lc, c ch hot ng quang hp, thc y hot ng h hp, lm mt cn i trong hot ng trao i cht ca c di, ngn tr s vn chuyn in t, ngn tr s tng hp cc acid amin, cc cht lipid... Cui cng lm cho c di thiu nng lng, cy di b cht.

1.4 NHNG NHN T NH HNG N TNH C CA CHT C gy c mt tc ng no n c th sinh vt, cht c phi xm nhp c vo c th, lu li trong mt khong thi gian nht nh v c c th ng ha, t tc ng ln cc c quan, hy hoi cc chc nng ca th sng. Tnh c ca cht c ph thuc vo cc nhn t sau: tnh cht ca cht c, c im ca sinh vt b cht c tc ng v nhng yu t mi trng khi p dng cht c.

1.4.1 S lin quan gia tnh cht ca cht c v tnh c ca cht cCc c tnh sau y ca phn t cht c c lin quan cht ch n cht c: - S hin din ca gc sinh hc c trong phn t cht c. Gc sinh hc l mt nguyn t hay mt nhm nguyn t to nn tnh c ca cht c, chng thng gy ra nhng triu chng ng c c trng khi tc dng ln dch hi. ng vi tng gc sinh c thng c mt dy cc hp cht c kh nng gy c, t nhng hp cht ny ngi ta chn ra mt s hp cht dng trong BVTV. V d nh cc hp cht thy ngn c tnh c nh s c mt nguyn t thy ngn trong phn t, mt vi hp cht thy ngn c chn lm thuc tr su, bnh (falizan...). - Hot tnh ha hc ca cht c cng cao th tnh c ca n cng cao. Anhydricasenno (As2O3) do c hot tnh cao hn nn c tnh c cao hn Anhydric asenic (As2O5). Vi cc cht hu c, thng cc hp cht khng no c hot tnh cao hn do c tnh c cao hn so vi nhng hp cht no. - Thnh phn ha hc ca phn t cht c: S thm, bt hoc thay th mt nhm nguyn t no trong phn t, d nhm c mt gc sinh c hay khng u dn n s thay i t nhiu tnh c ca hp cht. Khi thay th gc ethyl trong phn t thuc tr su parathion bng cc gc methyl s thu c thuc tr su mi l methyl parathion (wofafox); khi nh thm mt gc mthyl vo vng phenyl ca phn t methylparathion li thu c mt loi thuc tr su khc l sumithion. Tnh c ca 3 loi thuc trn khc nhau r rt: LD50 i vi chut ca parathion ch c 6-8 mg/kg, ca methyparathion tng ln n 25-50mg/kg v ca sumithion li cn tng ln nhiu na: 242-433mg/kg.

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C2H 5O C2H 5O

O P O NO 2 CH 3O CH 3O

S P O NO 2

Parathion LD50: 6-8 mg/ kg

M etyl parathion LD50: 25-500 mg/ kg

CH 3O CH 3O

S P O NO 2 CH 3

Sumithion LD50: 242-433 mg/ kg- Cu trc phn t: Cch sp xp cc nguyn t trong phn t i khi c nh hng rt ln n tnh c ca hp cht . Cc ng phn khng gian thng c tnh c rt khc nhau. Trong s cc ng phn ca BHC ch c ng phn gama l c c cao nht, cc ng phn kia rt t c i vi cn trng. - Tnh phn cc ca cht c: Cc cht phn cc khng c s phn b din tch ng u trong phn t v c xu hng d tan trong cc dung mi phn cc, cc cht ny thng xm nhp vo t bo bng cch chui qua nhng l nh trn mng nguyn sinh, do khi th tch phn t cng tng th tc xm nhp ca chng cng gim. Cn cht khng phn cc thng c xu hng d tan trong cc dung mi khng phn cc, do chng thng thm thu qua cc lp lipoit xm nhp vo t bo. Th tch phn t cht khng phn cc cng ln th tc xm nhp vo t bo cng ln nu nh s tng kch thc phn t dn n s gim phn cc. Trong cc hp cht hu c th cc nhm gy phn cc ph bin nht l hydroxyl, cacbonyl v cc nhm amin. Ngc li, cc nhm metyl, etyl, phenyl t gy phn cc phn t. - Mc in cng nh hng n tc xm nhp ca cht c vo t bo. Cc cht phn cc mnh c th phn ly ra thnh cc ion. Cc ion t do, ngay c trong trng kch thc ca chng nh hn kch thc l trn mng nguyn sinh, cng c khi xm nhp rt km hay thm ch khng xm nhp c vo t bo. iu ny c gii thch l do s tch in b mt ca mng nguyn sinh cht v lc ht tnh in gia mng tch in ny vi cc ion t do. Cng c khi cc ion bm trn mng nguyn sinh cht ph hy mng ny xm nhp vo t bo. - Kch thc cc ht thuc rn cng nh hng n s xm nhp ca thuc vo c th cn trng, ht thuc c kch thc qu ln s kh vo ming cn trng. Mt khc, kch thc ht thuc cng nh th tng din tch b mt ca n cng ln v do chng c ha tan v hp thu vo c th dch hi cng d dng.

1.4.2 S lin quan gia c im ca sinh vt vi tnh c ca cht ca. Tnh mn cm v tnh chng chu ca sinh vt i vi cht c Sau khi p dng thuc tr dch hi, thng thng phn ln cc c th dch hi b tiu dit, ch c mt s t cn sng st v nhng l do sau:----------------------------------------------------------------------------------------------------------------------------------------------------PGs. Ts. Trn Vn Hai

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- Do cc c th ny khng tip xc vi thuc hoc thuc ch xm nhp vo c th chng liu lng di liu gy cht. - Do chng tr thnh chng chu i vi thuc. Trong cc l do trn, l do th ba l quan trng nht. Chng ta thng ch quan tm n s dch hi b tiu dit (t l su, c di, chut b dit l bao nhiu? Ch s bnh, t l bnh gim bao nhiu?). Tt nhin s quan st ny l cn thit l mi quan tm trn l ng n. Tuy nhin c mt s iu quan trng khc ng c quam tm l cc c th cn sng st sau khi p dng thuc, s c th ny c th s pht trin thnh nhng trn dch, tai ho tht s i vi sn xut. Khi p dng mt loai thuc tr dch hi, cc c th cn trng hay cc tc nhn gy hi khc mn cm vi loi thuc s b tiu dit. C th mt s c th s khng b tiu dit nh c kh nng chng chu c vi thuc liu lng, nng p dng. Ni chung, tnh chng chu thuc ca dch hi ph thuc vo thnh phn loi, tui, tnh trng sinh l, cu to hnh thi, thnh phn men trong t bo... tu thuc vo bn cht ca thuc v iu kin p dng thuc. Do cn trng v nhn l nhng dch hi c kh nng khng thuc mnh nht, nn di y, ch yu chng ta cp n tnh mn cm v tnh chng thuc ca cc loi ny. * Tnh mn cm thuc ca dch hi: - Tnh mn cm thuc ca dch hi thay i theo tng loi thuc. Mt loi dch hi c th mn cm vi loi thuc ny nhng li chng chu c vi loi thuc khc. BHC c hiu lc cao trn nhiu loi su n l nhng li km tc dng i vi b ry, trong khi cc thuc carbamat nh: Mipcin, Bassa li c hiu lc cao i vi cc loi b ry. - Tnh mn cm thay i theo qu trnh pht trin ca c th. Thng thng th vi cng mt loi thuc, giai on trng v nhng, cn trng c sc chng chu cao hn so vi cc giai on khc (u trng, thnh trng). i vi u trng th tnh chng chu ca chng thng tng theo tui, trc khi lt xc cn trng chng chu kho hn l sau khi lt xc. Cn trng thi k nh dc qua ng c kh nng chng chu rt cao i vi thuc. Gia con c v con ci cng c s sai khc v tnh chng chu, ni chung con c thng mn cm vi thuc hn con ci. - Tnh mn cm ph thuc vo tnh trng sinh l v hot tnh sinh l ca sinh vt. Khi hot tnh sinh l ca cn trng tng ln th kh nng ng ha cht c cu n cng tng ln, lm cho cht c c hp thu v chuyn ha cng nhiu. Ngi ta cn phn bit cc c th chng chu thuc ra thnh nhng c th c kh nng chu ng c thuc v nhng c th c tnh khng thuc. * Thut ng chu ng c dng ch nhng c th dch hi c kh nng chu ng c mt lng cht c cao hn so vi liu lng thng dng ch trong vng i ca c th . Tnh chu ng thuc ca dch hi thng thay i theo tng c th, tnh trng sinh l ca c th. * Thut ng khng thuc (cn gi l tnh quen thuc hay tnh min dch) dng ch nhng c th dch hi c kh nng chu ng c cht c liu lng, nng bnh thng hoc cao hn v c tnh ny c th di truyn li cho th h sau. Hin tng dch hi khng thuc l mt qu trnh chn lc t nhin trn c s bin d v di truyn. Trn thc t, y l mt trong nhng v d in hnh v s tin ha theo hc thuyt Darwin, nhng ch khc l din ra vi mt nhp ht sc nhanh chng. S bin d thng----------------------------------------------------------------------------------------------------------------------------------------------------PGs. Ts. Trn Vn Hai

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xuyn xy ra trong qun th dch hi- ngay c khi khng b thuc c tc ng, v c tnh khng thuc cng ch xut hin mt cch ngu nhin. Cc c th c c c tnh ny s khng b dit bi thuc c sau khi p dng thuc v do chng s dng lun phn thc n ca nhng c th khng c c tnh khng thuc b tiu dit, iu ny lm cho mt s cc c th khng thuc tng ln rt nhanh. Mt s dch hi tng theo cp s nhn, nn lc u mt s thng tng chm nhng sau tng nhanh mt cch t ngt, gy ra nhng trn dch c sc tn ph rt ln. Hin nay hin tng dch hi khng thuc kh ph bin v ng lo ngi, nht l i vi su hi v nhn. nc ta, su t hi bp ci Plutella xylostella nhiu vng trng rau khng rt mnh thuc nh DDT, Wofatox, Dipterex... Ngoi ra kh nng khng thuc ca rp Myzus persicae hi rau h ch thp H Ni, ca ry nu Nilaparvata lugens hi la ng Bng Sng Cu Long cng kh quan trng. Ngi ta phn bit hai kiu khng thuc ca dch hi: khng chuyn bit v khng cho. + Khng chuyn bit (hay tnh chng chu chuyn bit, specific resistance): Dch hi ch khng thuc thng xuyn c p dng phng tr n ti mt vng nht nh. + Khng cho (tnh chng chu bt cho, cross resistance): L hin tng khi mt loi dch hi hnh thnh tnh khng i vi mt loai thuc ny th ng thi n c kh nng khng c nhng loi thuc khc m n cha h tip xc. Nhng loi thuc m mt loi dch hi khng c s hp thnh ph chng chu (resistance spectra) (hay ph khng cho - cross resistance spectra) ca loi dch hi . Nhng thuc ny c th c nhng c im nh thnh phn, cu trc v tc ng tng t vi thuc, thm ch i khi khc hn vi thuc m dch hi quen. + Trng hp ngc li, tc l khi dch hi quen vi mt loi thuc no th li tr nn rt mn cm vi mt loi thuc khc, c gi l hin tng chng chu bt cho m. V d nh b ry xanh ui en N. cinticeps v b ry nu Laodelphax striatellus khi quen vi Malathion th tr nn rt mn cm vi DDT v Lindane. Kh nng chng chu thuc ca cn trng thng do cc nguyn nhn sau: - Nh cc phn ng t v ca cn trng: nn ma, tiu chy, ng l th... - Nh cc c trng cu to hnh thi gii phu ca sinh vt, (cu to biu b, lng bn ngoi biu b...). - Nh cc phn ng ha hc, phn ng sinh ha phn gii cht c xy ra d dy, huyt dch, trong t bo. b. C ch hnh thnh tnh chng chu thuc ca cn trng Cc loi cn trng c th chng chu c vi thuc c th do: + Thay i v cu to hnh thi ca c th. Nhiu tc gi chng minh rng cc loi rui nh khng DDT c t bn chn dy hn, kh thm thuc hn so vi rui mn cm vi thuc ny. Otto D. (1976) cng nu ln nhng thay i v cu to ca lipoit, sp v protein trong cutin, hoc s gia tng kt cng biu b ca cn trng lm gim kh nng xm nhp ca thuc tr su vo c th cn trng.----------------------------------------------------------------------------------------------------------------------------------------------------PGs. Ts. Trn Vn Hai

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+ Tnh chng thuc ca cn trng c trng hp do kt qu ca s hnh thnh nhng tp tnh c bit, c tc dng ngn chn hoc hn ch s tip xc ca cn trng vi thuc tr su. Nhng cn trng thng gy hi vo ban m v tr n ban ngy nh su xm, nu p dng thuc vo ban ngy th n t c kh nng b nhim c thuc. + S gim st nhy cm ca nhng v tr tc ng ca thuc. Nhiu tc gi cho rng nhng qun th su chng thuc to thnh mt lp lipit c tc dng ngn cn s xm nhp nhanh chng ca cht c vo cu trc tinh t ca h thn kinh, v dn dn lm cho thuc mt tc dng. C nhiu loi cn trng v nhn chng c cc thuc tr su ln hu c v carbamat do men nhy cm cholinesteraza tr nn tr (km mn cm) i vi cc thuc ny. + C ch chng thuc quan trng nht, ph bin nht l tnh chng chu sinh l. Cn trng tng cng s gii c thuc hoc lm gim hot tnh ca thuc bng cc qu trnh chuyn ha. Trong c th cn trng chng thuc DDT, men DDT- aza c kh nng kh Hydrocarbon ca DDT di s hin din ca men DDT- aza lm cho hp cht ny b thoi bin. Trong c th cn trng chng cc thuc Cyclodien, thuc b c lp bi cc th protein... Trong s cc c ch trn, hai c ch sau quyt nh kh nng khng thuc ca cn trng. S hnh thnh tnh khng thuc ca dch hi th hin kh nng thch nghi tn ti ca sinh gii trn c s bin d v di truyn theo qui lut tin ha ca sinh vt, v vy ta ch c th lm gim tc ch khng th ngn chn s hnh thnh khng thuc ca dch hi. Trn c s l lun v c trong thc tin cho thy rng nu ch da vo bin php ha hc phng khc phc tnh khng thuc th sm mun g cng tht bi. Trn thc t, c nhiu ngi tng liu lng, tng nng thuc, tng nhp phun thuc u khng lm gim bt tc quen thuc ca ch hi, thm ch dch hi cn hnh thnh tnh khng thuc nhanh hn. Cch tt nht c th kim hm tc quen thuc ca dch hi l xy dng h thng cc bin php phng tr tng hp. Trong cn ch trng mt s bin php sau: - Xy dng mt ch lun canh cy trng hp l. Tuy nhin cc cy trng lun canh phi khng nm trong ph k ch ca loi ch hi tng gy hi trc y. - Thc hin kim tra cht ch v x l kp thi ngun su u v, tp trung cc vn m cy con thnh mt khu kp thi pht hin su mi n v phun thuc tr. - Thc hin cc bin php khc ngoi bin php ha hc lm gim mt s su trn ng rung nh xen canh vi nhng cy trng c tc dng xua ui su (nh c mc, c chua xen vi bp ci...). - Khi cn thit phi phun thuc, phi tun th nguyn tc 4 ng: dng ng thuc, dng ng lc, ng liu lng (hay nng ) v ng cch.

1.4.3 nh hng ca mt s ngoi cnh n tnh c ca cht cCc yu t ngoi cnh gm nh sng, m, nhit ... mt mt c th nh hng n l, ha tnh ca cht c, mt khc cng nh hng n trng thi sinh l v hot tnh sinh l ca dch hi. a. Cc yu t ngoi cnh i vi dch hi Tnh thm ca mng nguyn sinh cht c th thay i r rt theo iu kin ngoi cnh (pH mi trng, nh sng, nhit ...). di tc ng ca tia t ngoi, ca nhit , tnh thm ca t----------------------------------------------------------------------------------------------------------------------------------------------------PGs. Ts. Trn Vn Hai

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bo tng ln r rt. Khi nhit tng n im ti thch, hot ng sng (h hp, trao i cht...) ca cn trng v cc loi dch hi tng ln mnh m, km theo l s tng tc hp thu cc cht, a n kt qu l tng kh nng ng c ca dch hi. Tuy nhin trong mt s trng hp, s tng nhit mi trng lm tng tnh chng chu ca dch hi. S tng nhit trong mt gii hn nht nh lm tng hot tnh phn gii ca men DDT- aza,lm cho kh nng phn gii DDT ca cc loi rui nh c cha men ny tng ln. m trong t v trong khng kh cng nh hng n qu trnh sinh l ca dch hi, t nh hng n mc mn cm thuc ca chng. b. Cc yu t ngoi cnh i vi thuc tr dch hi - Nhit i khi cng nh hng rt ln n tnh c ca thuc tr dch hi; nht l i vi cc loi thuc c tnh xng hi, khi nhit tng, cc thuc ny bay hi cng mnh, lm tng nng tc ng v do tng kh nng tr dch hi. - m khng kh v m t thng c nh hng nhiu n s ha tan v thy phn ca cht c. m khng kh gip cho bordeaux ha tan thnh dng c th gy tc ng ln nm bnh. Cc thuc tr c thng ch pht huy tc dng khi t m. - Lng ma va phi lm tng m t, do lm tng tnh ha tan ca thuc trong t. Sau khi ma, nu phun thuc bt th thuc s bm dnh trn l tt hn. Tuy nhin, lng ma qu ln thng lm cho thuc phun trn l b ra tri, thuc phun trn t b cun i theo nc hoc lng xung nhng lp t su, va khng c tc dng tr dch hi, va gy nhim mi trng. Do cc keo t c kh nng hp ph cc cht, trong c c cc cht c dng lm thuc tr dch hi, nn nhng ni t c nhiu st, nhiu cht hu c th kh nng hp ph cht c cng cao. Nhiu khi thuc dit dch hi tt, cn phi tng liu lng ln cao hn so vi khi dng trn nhng t ngho cht hu c, thnh phn c gii nh. iu ny c bit quan trng i vi nhng thuc tr c c tc ng chn lc km, cho nn cn ch khi s dng va t hiu qu cao va khng nh hng n cy trng. Mt trong nhng tc nhn quan trng phn hy thuc trong t l cc vi sinh vt sng trong t, nu iu kin t ai cng thun li cho s pht trin ca nhng vi sinh vt ny th cht c b phn gii cng nhanh chng.pH trn cy trng v trong t cng nh hng rt ln n tnh c ca thuc, nhng ni c pH t cao, khi s dng nhng thuc k kim nh Kitazin 10H, chc chn hiu qu ca n s b gim. Mt khc pH t cng nh hng kh nng phn gii thuc.

1.5 THUC BO V THC VT V S BIN I CU TRC QUN TH SINH VTH sinh thi l mt phc h bao gm cc yu t nh t ai, kh hu, thy vn, ng vt, thc vt, vi sinh vt... H sinh thi t nhin rt a dng, phc tp v c tnh cn bng ng nn kh n nh. S khai khn, trng trt ca con ngi bin h sinh thi t nhin ny thnh h sinh thi nng nghip n gin, d bin ng. Cc bin php thm canh, canh tc c bit l vic dng cc ha cht c phng tr dch hi cng pht trin th s mt cn bng ca h sinh thi cng tr nn nghim trng. S pht sinh thnh dch ca cc loi gy hi l mt bng chng hin nhin ca s mt cn bng ny. Khi phn tch vic phun thuc, ngi ta c tnh ch c khong 10-20% lng thuc dng bt v 20-25% lng thuc dng lng bm trn cy; cn lng thuc thc s xm nhp, tc ng n su hi ch chim khong 1%. Ngoi ra khi l rng, lng thuc bm trn l cha phn hy ht s tch t li trong t. Phn thuc d tn ny s tc ng ln nhng sinh vt khng thuc i tng phng tr. Khi p dng thuc BVTV, cc tc ng xy ra ng k nht l:----------------------------------------------------------------------------------------------------------------------------------------------------PGs. Ts. Trn Vn Hai

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Chng 1

1.5.1 Thuc BVTV vi qun th dch hiSau khi p dng thuc, phn ln cc c th loi gy hi b tiu dit, tuy nhin mt s c th c tnh khng thuc s khng b cht, s ny s tng ln theo cp s nhn v nhanh chng tr thnh mt qun th dch hi khng thuc. Di tc ng ca thuc, mt s loi gy hi th yu cng b tiu dit. Tuy mhin c khi mt s loi gy hi th yu c kh nng khng thuc mnh s pht trin thnh loi gy hi ch yu rt kh phng tr. Khong nm 1950, loi gy hi ch yu trn bp ci c ghi nhn l su xanh, nhng sau mt thi gian dng thuc ha hc lin tc, su t tr thnh loi gy hi ch yu vi tnh khng thuc rt mnh. Phng tr su t l mt vn nan gii hin nay.

1.5.2 Thuc bo v thc vt vi nhng sinh vt c chThuc bo v thc vt mt mt tiu dit hng lot cc c th gy hi, lm cho cc loi thin ch thiu thc n, mt khc chnh cc loi thin ch ny cng b thuc tiu dit. Cc loi sinh vt c ch khc cng b nh hngi khi rt nghim trng. l ong, bm v hi gip cho cy th phn, giun t v cc loi cn trng sng trong t chuyn n tn tch thc vt, lm cho t ti xp v cung cp thc n cho cc loi vi sinh vt tip tc phn gii thnh nhng cht dinh dng cung cp cho cy trng, duy tr mu m ca t. Cc thuc tr dch hi, nht l cc thuc tr nm, c th tiu dit nhng vi sinh vt c ch khc nh nhng vi khun nitrat ha, vi khun nitrit ha, c nh m trong t. Ngoi ra thuc BVTV cn nh hng n gia sc v cc ng vt c xng sng vng c p dng thuc.

1.5.3 Thuc bo v thc vt i vi cy trnga. Tc ng c li ca thuc bo v thc vt i vi cy trng Cc thuc bo v thc vt tiu dit cc loi k sinh hoc cnh tranh iu kin sng vi cy trng (nh su, nm bnh, c di), gip cho cy trng pht trin tt, cho nng sut cao. Nu khng tr c th cy la ch hp thu mt lng N bng 52-70% so vi tr c, do nng sut c th b gim 18-43% (Arai Masao A., 1996). Mt s thuc bo v thc vt cn c kh nng kch thch qu trnh sinh trng v pht trin ca cy trng: Nng cao t l ging ny mm, ci thin s pht trin ca b r, tng chiu cao cy, s ht trn bng, trng lng ht, t l ht chc, hoc lm cho cy trng vng vng, cng cp hn. Thuc tr nm kitazin P dng ht khi bn vo rung tr bnh o n hi la lm cho thn la mp hn, hn ch chiu cao cy nn chng c lp . b. Tc hi ca thuc BVTV n cy trng Nu s dng khng ng thuc, khng ng liu lng, phng php thuc c th gy hi cho cy trng. Triu chng v mc b hi kh a dng. Cht c c th gy hi trc tip ngay ti ni thuc tip xc vi cy trng, triu chng b hi thng rt c trng v c th biu hin ngay sau hoc sau mt thi gian di. Cc thuc tr nm thy ngn hu c, thuc gc ng nu dng nng qu cao, mt ngy sau khi dng thuc l v nhng chi non c th b ho v en; thi tit cng nng, tc hi cng ln. Thuc tr c 2,4-D c th lm cho thn c chua b cong queo, l mc d hnh... Mt s thuc khng gy hi cho cy trng nhng li nh hng n phm cht nng sn. BHC k ngh c th lm cho c khoai ty, ch, thuc l c mi hi rt kh chu.

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21


Chng 1

Ni chung, tc hi ca thuc BVTV ph thuc vo nhiu yu t: Bn cht ca thuc, loi cy trng, iu kin ngoi cnh. an ton ca thuc BVTV i vi cy trng c th biu th bng ch s ha tr liu: c K= ........... t K: Ch s ha tr liu c: Liu gy cht ti thiu ca thuc i vi dch hi t: Liu ti a ca thuc m cy chu ng c (toxic tolerant) Tr s K cng nh, thuc cng an ton i vi cy trng, thng nhng thuc c tr s k 1 ch c dng lm b c hoc x l trn nhng khu t khng c cy trng pht trin. C th thuc ch gy hi cho mt s cy trng. DDT, BHC t ra an ton i vi nhiu loi cy trng, nhng cy thuc h bu b li rt mn cm vi cc loi thuc ny. Thuc tr c DCPA c th gy hi cho nhiu loi cy trng, nhng c dng tr c cho la do la c kh nng chu ng thuc ny rt tt. iu kin mi trng i khi cng h tr cho iu kin gy hi cy trng ca thuc. Thuc tr nm lu hunh bt khi s dng trong iu kin nhit mi trng cao c th gy chy l. Nhng thuc BVTV c bn vng ln, c th tch t li trong t v gy hi cho cy trng cc v sau. Trn t ct pha ven sng y H Ni, khi dng Simazin v Triazin phun cho ng vi lng 4-5kg/ha c tc dng tr c cao. Tuy nhin sau khi thu hoch ng, lm t gieo tip u hoc la m cc cy trng ny s b gy hi nng (pht trin km, cht cy con, nng sut thp). Bn cnh nhng yu cu thng c t ra i vi thuc BVTV nh kh nng dit dch hi cao, an ton i vi con ngi, cc sinh vt c ch, thin ch, cy trng...cng cn c nhng lu thch ng n tc ng ca thuc ln cn bng sinh thi, s tn d v gy nhim mi trng ca thuc. Hin nay ngi ta ch s dng nhng thuc c tc dng dit dch hi cao nhng bn va phi ( c th phn hy trong mt thi gian ngn sau khi tiu dit dch hi); nhng thuc c tnh chn lc cao, nhng thuc c kh nng lu dn. -------oOo--------

Cu hi n tpCu 1: Phn loi thuc tr dch hi theo phng php thm thu v c tnh tc dng? Cu 2: Hiu th no v s xm nhp ca cht c vo c th cn trng?

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22

Gio Trnh Ha Bo V Thc Vt

Chng 2

CHNG 2: CC PHNG PHP S DNG v TH NGHIM THUC TR DCH HI2.1 CC DNG CH PHM DNG TRONG BO V THC VTCc ch phm dng trong BVTV cha hai thnh phn ch yu l hot cht v cht ph gia. Thnh phn ch yu ca thuc l hot cht (cht hot ng - active ingredient, a.i.), l thnh phn mang hot tnh tr dch hi. Trong sn xut cng nghip, cc hot cht thng c ln mt t tp cht, c gi l thuc k thut hay thuc ng k ngh. Ngi ta t khi s dng hot cht dng nguyn cht m thng l gia cng to thnh cc ch phm khc nhau bng cch trn thm vo cc cht ph gia nh cht n, cht nh ha... Cc cht ph gia s gip cho vic pha ch, chuyn ch, bo qun v s dng c thun tin hn, hu hiu hn. Cc ch phm dng trong BVTV c th chia thnh hai nhm sau.

2.1.1 Nhng ch phm cn ha long trc khi s dngNhng ch phm ny thng c ha vi mt lng dung mi nht nh cho n khi t c nng s dng c qui nh cho tng loi ch phm. Dung mi thng dng l nc. Trong mt s trng hp c th s dng nhng dung mi khc, nh thuc tr c PCP (pentaclophenol) c ha chung vi du diezen phun tr c. Nhm ny gm c cc dng sau: a. Bt thm nc (BTN, BHN - bt ha nc WP - water wettable powder, DP - water dispersible power): cc ch phm ny thng cha 25-80% hot cht, khi ha vo nc s to thnh mt huyn ph tng i bn vng. Yu cu: kch thc cc ht phai ng u v ng knh nh hn 3; khi ha thuc vo nc, dng huyn phi nhanh chng c to thnh nhng chm lng ng; tnh thm t, tnh tri rng v tnh loang tt, sau khi nc bay hi, thuc phi cn bm li trn b mt x l trong mt thi gian di. Mt s dng thuc khc khi ha vo nc cng to thnh huyn ph: Bt keo (colloidal powder): Ging nh thuc BHN nhng kch thc cc phn t rt nh nn rt lu lng, bm dnh tt m khng cn thm cht bm dnh hay cht n nh. Cc thuc gc ng v cc thuc gc lu hunh nguyn t thng c c tnh ny. Huyn ph (HP, Suspension): Ch phm dng huyn ph m c, pha long dng nh thuc BHN (nh Oxychlorur ng 20 HP). Thuc nho (Paste): Ch phm dng nho nh kem, c hm lng v cch dng nh thuc BHN. Thuc c pha thnh dng huyn ph m c qut ln vt thng ca cy hoc dng x l ging, cng c khi pha long vi nc s dng nh BHN (thuc Bordeaux thy c bn di dng ny).

b. Nh du (ND: thuc sa, thuc sa m c; EC: Emulsive concentrate): dng ch phm nay thng cha 30-50% hot cht, khi ha vo nc s to ra nh tng kh n nh. Ch phm thng c thm vo cc cht hot ng b mt khng ion ha hoc anion lm cht nh ha. c. Thuc lng tan trong nc (SS: soluble, DD: dung dch hay L- Liquid, SC: suspension concentrate, FL: flowable Liquid): Khi ha vo nc, thuc s tan hon ton trong dung dch. --------------------------------------------------------------------------------------------------------------------------------------- 23PGs.Ts. Trn Vn Hai


Chng 2

d. Bt tan: (SP: soluble powder): Khi ha tan vo nc s to thnh dung dch.

2.2.2 Nhng ch phm khng ha long trc khi p dngGm nhng thuc c th p dng trc tip ln cy trng hoc nhng i tng cn x l khc m khng phi ha vo dung mi no c. Nhm ny gm nhng dng sau: a. Bt phun (Bt rc - BR, D - Dust): Kch thc ht thng nh hn 44. Ch phm thng cha 4 - 10% hot cht, c dng phun dng kh nh bi. Yu cu: t trng v kch thc ht phi c ch to sao cho va nh khi phun, gi c th mang thuc i mt lng ng k nhng ch trong phm vi phng tr, lng thuc lng im cch my phun 5m v im cch my phun 20m phi tng ng nhau. So vi cc thuc phun lng nh BTN, cc thuc phun bt d s dng hn, nht l nhng ni thiu nc pha thuc, d p dng trn nhng din tch ln; tuy nhin lng thuc bt b hao ph trn mt n v din tch nhiu hn do thuc d b gi cun i v do bm dnh km nn d ri xung t. tng cng tnh bm dnh, ngi ta thng gn hot cht ln nhng cht mang. b. Thuc ht (H,G = granule): Ht to ng knh thay i trong khong 297-1680. Thuc c dng ri bng tay hoc bng my ln rung, sau trn u vi t bng cc cng c. Lng thuc dng trn mt n v din tch thng phi ln hn so vi nhng phng php khc. Loi thuc ny thch hp cho nhng trng hp cn thuc c tc dng lu di. Ngoi ra cn c cc dng trung gian gia thuc bt v thuc ht nh thuc bt ht (dust granule) hay cn gi l vi ht (microgranule) vi ng knh ht thuc nm trong khong 44 297 gm c hai dng: thuc bt th (coarse dust) c c ht t 44 - 105 v thuc ht mn (fine granule) c c ht t 105 - 297. Ngi ta cn dng cc thuc hn hp ca nhiu c thuc ht k trn. c. Thuc phun m (aerosol), thuc phun th tch cc thp (UVL), th tch cc - cc thp (UULV): Nhng thuc ny gm c hot cht c trn vi mt t dung mi hu c v thng c dng nguyn dng ch phm ch khng ha long. Cc dng thuc ny c s dng dng lng bng nhng my bm c bit nh my phun m, my ULV. d. Thuc xng hi: Thuc dng lng rn hay kh nn. Khi dng, thuc bin i thnh dng kh hay dng hi (c i khi dng thng hoa) ha vo khng kh v t tc ng ln dch hi.

2.2.3 Cht ph giaL nhng cht c trn vi hot cht nhm ci thin tnh cht l, ha hc ca thuc, to iu kin cho vic pha ch, chuyn ch, bo qun v s dng c d dng, tin li hn. Cc cht ph gia thng c dng l: a. Cht n (cht mang, cht ti - carrier): gm nhng cht c tc dng lm gim bt hm lng cht c c trong ch phm, nhm lm cho vic ri mt lng cht c nh trn mt n v din tch ln c d dng hn. Cht n phi mang tnh tr, khng tc dng vi cht c, khng gy hi cy trng,v.v... Nhng cht n nh Attapulgite, kaolin, bt talc, pyrophyllite, bentonit, diatonit, thng c mt trong cc dng thuc bt v thuc ht.--------------------------------------------------------------------------------------------------------------------------------------- 24 PGs.Ts. Trn Vn Hai


Chng 2

b. Cht to huyn ph (suspensible agent): L nhng cht to nn s tng hp gia nc v cc ht thuc rn, qua to iu kin hnh thnh mt huyn ph bn ca thuc trong nc. Thuc BTN thng cha khong mt vi phn trm cht to huyn ph nh bt kh du, bt b hng, bt b kt. c. Cht nh tng ha (emulsible agent): L nhng cht to nn s tng hp gia nc v cc git cht c th lng thuc nh du, lm bn nh tng to thnh. V d nh cc cht nh tng ha. d. Cht tm t (wetting agent), cht loang (cht tri rng - spreader): C tc dng lm t mt phun v lm cho cc git thuc (huyn ph, nh tng, dung dch) loang u trn mt vt phun. e. Cht kh ng t: lm tng tnh bn ca huyn ph bng cch ngn cn cc ht thuc lin kt li vi nhau thnh nhng phn t ln hn. f. Cht dnh (sticker): gip thuc gn cht vo b mt phun, gp phn to nn mt lp thuc bo v bn cht trn b mt vt phun. Cht dnh thng dng l nhng loi du, nhng glixerit khan, canxi sunphat, nhm hydroxyt v.v. g. Cht trung ha (cht bo v cy): C tc dng kh nhng cht c hi cho cy cn ln trong ch phm. h. Cht ho ha: ni chung nhng cht ny c tc dng ci thin cc tnh cht vt l ca ch phm. V d trong thuc bt, nu ta thm vo 3 - 5% du khong (du xola, du nng, du bi trn my). Du s gip cho cc ht nh kt t li, khng b gi cun i xa v lm tng tnh bm dnh ca thuc . Trong nhiu trng hp, mt cht ph gia c th tc dng nhiu mt: nh ha, tm t, n nh, bm dnh... c bit l nhng cht hot ng b mt nh x phng, b ru - sunphit m c. Cc cht hot ng b mt c th phn ly thnh ion trong nc thnh cc ion, cng c cht hot ng b mt khng phn ly. Trong nng nghip thng s dng nhng cht hot ng b mt mang in tch m hoc khng mang in tch. * Nhng cht hot ng b mt thng dng l: - X phng lng, x phng rn, x phng naptenic. Cc loi x phng c dng lm cht n nh, cht nh ha, cht dnh, cht hot ha. - B ru - sunfit m c, l sn phm ph ca ngnh sn xut giy xellulose, c thnh phn ha hc l mui canxi ca axit licnosunphonic hn hp vi cht kh v cht khong v c. Trong nng nghip, b ru sunfit m c c sn xut di dng lng, rn, bt. Cc sn phm ny c hot tnh b mt cao v c dng rng ri lm cht n nh. Ngoi ra cn c nhiu ch phm tng hp khc c dng lm cht tm t, cht long nh casein, canxi cazeinat, saponin, cc axid sunfonic thm v bo, ru v..v.

2.2 CC PHNG PHP S DNG THUC TR DCH HI 2.2.1 Phun thucVic phun thuc nhm lm cho thuc c tri u trn khp b mt din tch cn c bo v ca cy trng, nng sn hay t tiu dit hoc ngn chn s ly lan, ph hoi ca cc loi dch hi, bo v cy trng v nng sn. Thuc bo v thc vt c phun bng cc loi eo --------------------------------------------------------------------------------------------------------------------------------------- 25PGs.Ts. Trn Vn Hai


Chng 2

vai thng thng, my bm eo vai, my bm gn trn my cy, trn my bay. C nhiu kiu phun thuc khc nhau, chng c phn bit ty theo trng thi vt l (rn, lng, kh), theo ln ca cc phn t thuc (git thuc, ht thuc) v lng dng trn mt hecta. Phun thuc lng l phng php c dng ph bin nht hin nay. a. Phun dng lng Cc dng thuc tr dch hi di dng BHN, ND, DD, c ha vo dung mi (thng l nc) to thnh cc dung dch phun (nc phun). Thuc phn tn vo nc thnh cc dng huyn ph, nh tng hay dung dch tht. Dng phun lng thng c a chung hn thuc bt phun kh do thuc phun u hn, thuc bm dnh trn b mt x l tt hn. Trong cc dng thuc phun lng, thuc dng huyn ph t xm nhp vo cy, tri hn so vi dng nh du nn t lu b c hn. Yu cu: hot cht phi bn vng trong nc thuc, khng b phn hy khi pha long. H phn tn phi tng i bn vng, lu lng t. Nc thuc phi c tnh thm, tnh loang tt v bm dnh bn lu trn b mt vt phun (Khi ri ln b mt vt phun, trc tin git thuc phi dnh vo b mt vt phun, tm t c b mt ny ri mi loang ra; khi kh nc, thuc vn cn bm cht trn b mt vt phun. m bo c yu cu trn, git thuc phi c sc cng b mt nh. C th lm gim sc cng b mt ca git thuc bng cch thm vo thuc cc cht hot ng b mt. Ngoi ra, ngi ta cn thm vo thuc cht bm dnh gip cho thuc bm cht vo b mt vt phun, to nn mt lp thuc bo v khi nc bay hi ht. Khi phun thuc, p sut phun phi ln thuc c phun ra u v ht thuc c ng nng dnh vo b mt x l). Vi cc thuc to thnh huyn ph trong nc phun: tc lng ca ht cht rn trong huyn ph ph thuc vo trng lng ring ca thuc v nht ca mi trng. Trng lng ring ca thuc c tnh bng khi lng thuc (tnh bng g) trn mt n v th tch (tnh bng g/m3) thng trng lng ring ca thuc nm trong khong 0.5 - 0,8 kch thc phn t nh hn 3 l tt. Khi thuc chm kt lng hoc ni ln, thuc phun ra u, t b nght vi phun, bo m kh nng tr dch hi cao. C th lm tng nht ca thuc bng cch thm vo ch phm cc cht n nh. Vi dng thuc nh du, kch thc phn t i hi phi nh hn 0,1. Ngi ta thng ngn nga s phn lp gia hot cht v dung mi, s hp nht cc git nh thnh cc git ln hn v lm cho thuc phn tn u hn trn b mt vt phun bng cch thm vo ch phm cc cht n nh, cht nh ha. C nhiu loi bm phun khc nhau c th dng phun thuc lng, tu theo yu cu v tu theo thit b s dng, kch thc phun c th rt khc nhau. Tu theo kch thc git thuc c phun ra, c nhiu kiu phun c p dng: Phng php ln git thuc (m) Phun nc (1) >150 Lng nc phun (lt/ha) Cy hng nm >200 (200 - 800) Phun ma bi (2) Phun ma bi mn (3) 50 - 250 25 - 125 (80 - 160) Phun m (4) 600 (600 - 1000) 200 3 - 20 (1 - 6) 3-6

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Chng 2

(80 - 120)

(< 0,5)

(< 0,5)

(1): Phun th tch trung bnh v cao. (2): Phun th tch thp. (3): Phun th tch cc thp (ULV). (4): Phun th tch cc cc thp (UULV) + Kiu phun nc vi th tch cao thng c thc hin bng cc bnh 10 lt, 20 lt eo vai bm tay, hoc c gn ng c. + Xn kh (aerosol, phun khi - vi thuc rn, phun m - vi thuc lng): bng nhng dng c c bit, c th phun thuc dng lng hay rn vi kch thc phn t rt nh, gi l nhng xn kh. Cc ht thuc ny s l lng trong khng kh trong mt khong thi gian nht nh v gy c cho dch hi. Phng php ny thng c dng tr su, nhn, nm bnh trong cc phng kn (kho, nh knh, toa tu...) v tr nhng cn trng bay nhy nhiu trn ng rung. Do kch thc ht rt nh nn phng php ny c mt s u im sau: Hot tnh cao do thuc c phn tn cao, xm nhp vo vt phun d dng. Tnh bm dnh tt. c vi dch hi cao hn do nng thuc cao. Lng nc cn dng nh (khong 20 lt ). Vi nhng phng php phun vi th tch cc thp (ULV) v th tch cc cc thp (UULV), th tch dung mi dng ch khong 1 - 4,6 lt/ha.

Tuy nhin thuc cng c nhng nhc im nh l lng rt lu trong khng kh, rt lu lng ng, d b gi cun i. c hot tnh vt l cao m khng b gi cun i xa, kch thc ht thng c yu cu phi nm trong khong 0,5 - 100 .). Thnh phn ca thuc gm c: hot cht ha tan vo du khong c nhit si tng i cao nh du xola, du my bin p, du diezen...; c th dng cc dung mi d bay hi nh CCl4... to thnh nhng git m, c th phun thuc di p sut hng trm atmosphere bng nhng thit b c tc vng quay hng vn vng/pht; hoc bng cch un ha nhit dung dch du ca thuc trong ni hi hoc qua nhng ng rut g lm ht thuc c bn ra khi my di p sut 7 - 8 atmotphe, ha vo khng kh lnh bn ngoi v ngng t thnh m c phn tn cao (ng knh git thuc nh hn 1). trnh dng p sut qu cao v trnh s phn hy thuc mt phn do nhit, ngi ta c th phi hp c hai phng php trn bng cch cho mt dng hi nng i qua dung dch thuc bc u to ra nhng git thuc c kch thc nh, nhng git thc ny khi n ming vi phun mi c un nng v bay hi, hoc phi hp c hai cch. b. Phng php ti t dit tr nhng dch hi sng trong t hoc vi nhng thuc ni hp c th ha thuc vo nc n nng bng nng phun v ti vo t. C th ti vo lc trc hoc sau khi ht ny mm, bng nhng bnh ti hoc bnh phun. Lng nc thuc phi c tnh ton sao cho thuc c th ngm n su khong 10 - 15 cm. Thuc cng c dng ti vo gc cy vi lng nc khong 50 200 ml/gc. c. Phun bt kh--------------------------------------------------------------------------------------------------------------------------------------- 27 PGs.Ts. Trn Vn Hai


Chng 2

Thuc bo v thc vt hin din dng bt, bt ht, bt th, ht mn pha ch sn sng phun ln cy hoc ln mt t bng cc my phun bt vi lng ch phm dng cho mi hecta khong 20 - 40 kg. Thuc ht ch yu dng phun hoc rc vo t vi lng ch phm khong 20 - 30 kg/ha. Yu cu: Bt phun ra phi bao ph u khp b mt x l, khng b gi cun i qu xa, bm dnh v gi li tt trn b mt x l. Cht lng bt phun ph thuc nhiu vo c tnh vt l v ha hc ca thuc bt, vo c im b mt vt phun. * Tc ri ca cc phn t thuc bt c tnh theo cng thc:

V =

2 gr 2 (D a) Y

Vi: v = tc ri t do ca cc phn t (cm/s). g = gia tc trng trng (981 cm/s2). r = bn knh ca cc phn t (cm). Y = ln ca kh quyn ( 10 - 30oC vo khong 0.00076 - 0.00086). D = t trng ca thuc bt. a = t trng khng kh (0.0001225). g, Y, a: xem nh hng s, v vy tc ri ca ht thuc ph thuc ch yu vo ln v t trng ca ht thuc bt. Thi gian ri ca cc phn t t cao h c tnh theo cng thc sau: t: thi gian ri ca cc phn t.t = h vt

h: cao. vt: tc ri t do theo phng thng ng.

T hai cng thc trn ta thy rng khi phun thuc bt c c ht to, t trng ln th tc ri t do s ln, thuc khng bay ra xa ni phun thuc. Tuy nhin nu c ht qu to, t trng qu ln th thuc li kh bm gi trn b mt vt phun. V kch thc, nhng ht c hnh cu d b ri khi mt l cy hn so vi nhng ht hnh a din. Hin tng bm dnh ca ht thuc ln b mt vt phun cn c gii thch nh sau: trong qu trnh chuyn ng, cc ht thuc bt c th nhim in do ma st; du v cng in tch ph thuc vo bn cht thuc v vn tc di chuyn ca ht. Khi ht thuc n gn b mt vt phun th theo qui tc cm ng in t s xut hin trn b mt vt phun in tch tri du a n kt qu l ht thuc bm gi cht vo b mt vt phun.--------------------------------------------------------------------------------------------------------------------------------------- 28 PGs.Ts. Trn Vn Hai


Chng 2

tng tnh bm dnh ca thuc, ngi ta thng trn thm cht ho ha, cht bm dnh... Hoc gn cc hot cht ln nhng cht mang. Kh nng bm dnh v gi li ca thuc cn ph thuc vo tnh cht b mt vt phun, thuc bt bm dnh v gi li tt hn trn nhng l nm ngang, c np nhn nheo, c lng hoc trn l m t do sng hay ma; kh bm gi li trn nhng l thng ng, mt l phng, lng, trn l kh. * u nhc im ca phng php phun bt so vi phng php phun lng: + u dim: n gin, thit b nh nhng, r tin hn v c th s dng trong nhng iu kin a hnh bt li. Thch hp vi nhng ni khng c sn ngun nc v cn phun trn din tch ln. + Nhc im: Phi dng mt lng thuc nhiu hn so vi phun lng trn mt n v din tch. Trn mi ha cy trng, lng ch phm thng dng l 30 - 50 kg/ha. Lng thuc hao ph ln do b cun tri bi ma, gi. Lng d tha ny d lm nhim mi trng.

2.2.2 Rc htThuc tr dch hi dng ht thng dng rc vo t tr cc loi dch hi sng trong t, cc loi thuc lu dn khi rc vo t c r hp thu v dn truyn ln cc b phn pha trn mt t dit tr su hi (rp, b phn trng Bemisia trn rau, c chua...) hoc cc loi nm bnh trong mt thi gian kh di. Cc thuc ny cn c dng rc ln cy nhm dit tr su c thn, su c ngn (Nh cc thuc tr su clo hu c, ln hu c thng c dng rc ln non ng tr cc su n l sng trong loa kn). Thuc c th c rc u trn ton b din tch x l bng tay hay bng my phun ht, my bay... hoc c th ch ri theo lung, theo tng gc cy. Yu cu: Thuc phi c rn chc nht nh, khng b v vn trc khi rc, khng b phn r qu nhanh khi p dng ln cy hoc ln t. Ht thuc rc vo t phi tan c dn vo nc t t cung cp cht c tiu dit cn trng, nm bnh, c di. thuc c rn chc, trong qu trnh ch bin ngi ta thng thm vo cc cht kt dnh. m ca t nh hng rt ln n ha tan ca thuc vo t, nhng thuc ht c tnh lu dn s khng pht huy c tc dng trong iu kin kh hn. Nhng thuc c tnh xng hi t chu nh hng ca m , c nhiu trng hp phi trn lp t mt hn ch s bay hi ca thuc vo khng kh v gi thuc nng cao trong t, lm tng hiu qu dit dch hi. Ngoi tc dng bo v cy lu di, thuc ht rc bng my bay hoc my phun thuc ln t t lm chy l cy, t gy nhim khng kh trong vng rc thuc. Phng php rc thuc ht tr c ngy cng c s dng rng ri.

2.2.3 Ni liu php thc vtL phng php a nhng thuc lu dn vo trong h thng cy trng, nhm gy ra mt trong nhng tc ng sau: + Lm cho cy tr nn c i vi dch hi (cn trng, nhn, nm, vi khun...) trng hp ny, cy c th chng li c c nhng dch hi chuyn tnh ln khng chuyn tnh. + Trung ha nhng c t hnh thnh trong cy do tc ng ca dch hi hay ca nhng yu t khc. --------------------------------------------------------------------------------------------------------------------------------------- 29PGs.Ts. Trn Vn Hai


Chng 2

+ Lm thay i thnh phn ca dch t bo ca cy, v bin i c im ca qua trnh sinh l, sinh ha ca cy, khin cho cy tr thnh khng cn ph hp vi dinh dng cc loi gy hi na. Trong trng hp ny, thng thuc ch c tc dng bo v cy chng li nhng loi dch hi chuyn tnh hp, v d nh nhng cc loi su n thc, nm v vi khun ch chuyn tnh cao. + Lm cho cy tr nn min dch i vi mt loi dch hi (min dch nhn to). + Cc yu cu khi thc hin bin php thc vt: nhng thuc lu dn ny phi xm nhp vo c bn trong cy, vi mt nng nht nh no gy hi cho dch hi, nhng thuc phi khng c cho cy v c kh nng phn hy trong cy trng sau mt thi gian nht nh tr thnh v hi i vi ngi v gia sc s dng nng sn, thc phm vng phun thuc. + Ni liu php bo v thc vt c th thc hin bng nhiu cch khc nhau vi nhng thuc lu dn: trn ht ging vi thuc, bn thuc vo gc cy, co lp v ngoi ca thn cy ri buc vng vi tm thuc, phun thuc lng ln cy. + Tc xm nhp ca thuc vo trong cy, s lan truyn, s tn ti ca thuc trong cy ph thuc vo c im ca thuc, loi cy, thi k sinh trng ca cy, iu kin ngoi cnh.

2.2.4 Xng hiDng nhng thuc c kh nng bay hi lm khng kh xung quanh dch hi b nhim cht c, nhm u c dch hi qua ng h hp. Phng php xng hi t ra c hiu qu cao khi c dng tr nhng sinh vt gy hi n nu nhng ni kn o nh k tng, trong cc kho hng, kho lng thc, khoang tu ch nng sn, trong nh knh, trong t. Phng php ny c dng tr chut, su hi, nhn, tuyn trng, nm, vi khun... Thuc dng xng hi c th dng rn, lng c p sut hi ln hoc dng kh nn. Cc thuc ny c th khuych tn trong khng kh trng thi kh hoc hi, i khi cn dng thng hoa. * Cc yu t sau y c nh hng n hiu qu s dng thuc xng hi: + Khng gian: Phi m bo duy tr khong khng gian dng thuc kn trong mt khong thi gian nht nh. Phng php xng hi thng ch c thc hin nhng ni kn o, do thuc c th kh hoc hi c kh nng khuych tn mnh, nn nu khng tin hnh trong mt khng gian c nh th hi c, kh c b ha long vo khng kh, khng duy tr c nng thuc tiu dit dch hi. + Cc c im vt l, ha hc ca thuc: nhng c im c nh hng mnh m n hiu qu dng thuc nh: bay hi, t trng hi, tc bay hi, kh nng khuych tn vo khng kh, kh nng b hp ph bi b mt vt c x l. + bay hi: L khi lng ti a ca cht c trong mt n v th tch khng kh mt nhit v p sut nht nh. n v tnh: g/m3. bay hi ca mt cht t l thun vi nhit mi trng, t l nghch vi p sut v nhit si ca cht xng hi. D nhin cht xng hi ch c tc dng khi bay hi ca thuc cao hn nng gy c cho dch hi. + Tc bay hi: c xc nh bng khi lng hi bay ln t 1cm2 b mt rn hoc lng ca cht xng hi trong thi gian mt giy. Tc bay hi t l thun vi nhit xng hi v t l nghch vi nhit si v p sut. Nhit khng kh v din tch b mt cao lm tng tc bay hi.---------------------------------------------------------------------------------------------------------------------

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