MANAGING INSECTS IN THE HOME VEGETABLE GARDEN Rick E. Foster and John Obermeyer, Extension Entomologists Department of Entomology Vegetable Insects E-21-W PURDUE EXTENSION Insects feeding on home-grown vegetables are a fact of life for most gardeners. Gardeners’ two choices are to tolerate the damage or attempt to prevent it. Frequently, tolerating the damage is a reasonable approach. For example, when tomatoes begin to ripen, most gardeners have more tomatoes than they can possibly use. So, caterpillars chewing on a few fruits are no real concern. Corn earworms usually confine their damage to the tips of sweet corn ears. A viable strategy is to cut off the damaged tips before cooking the corn. Another approach is to plant crops less susceptible to injury from insect feeding. Table 1 categorizes vegetable crops as never or rarely, sometimes, and usually or always damaged by insects. There are a number of practices that the home gardener can employ to reduce insect problems. • Properly dispose of plant residues from the previous year’s garden. • Plant varieties that are recommended for use in your area, and plant them at the proper time for best growth. Planting too early when the soil is cool may make the plants more susceptible to some soil insects. • Inspect transplants before purchase to make sure they are healthy and not infested with insects. • Use proper plant spacings, fertilizers, water, and cultural practices to insure vigorous plant growth. Plants that are growing vigorously often can tolerate more insect damage than poorly growing plants. • Keep the garden as weed-free as possible. This will help the plants to continue to grow vigorously, and weeds may harbor insects that also will attack the vegetables. However, the presence of weeds or companion plants may increase the natural enemy population. • Inspect plants regularly for insects or insect damage. Early detection means more effective control and can reduce the amount of damage suffered. Particularly in small gardens, early-detected caterpillars, loopers, hornworms, and large beetles can often be hand picked from plants and destroyed before they cause problems. • Treat most vegetables with insecticides only when pest insects are observed; however, treat certain vegetables, such as cantaloupes, cucumbers, and squash, on a preventive basis to avoid serious damage. INSECTICIDES Several types of insecticides are available for home gardeners. Table 2 lists the insects most commonly found on vegetables and the insecticides recommended to control them. The following sections describe the various types of available insecticides. Botanical Insecticides (extracted from plants) Neem: The active ingredient in Neem, azadirachtin, is derived from leaves or seeds of neem trees. It has activity against a variety of insect pests. For many pests, neem acts as a repellent, rather than a toxicant. Therefore, it is important to apply neem before a serious infestation is present. Pyrethrum is derived from the flowers of certain chrysanthemums. It causes rapid paralysis and apparent TABLE 1. Frequency of Insect Damage to Various Vegetables Grown in the Home Garden Never or Rarely Sometimes Usually or Always Carrot Asparagus Broccoli Green onion Bean Cabbage Lettuce Pepper Cantaloupe Pea Spinach Cauliflower Radish Tomato Cucumber Eggplant Potato Squash Sweet corn
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MANAGING INSECTS IN THE HOME VEGETABLE GARDEN
Rick E. Foster and John Obermeyer, Extension Entomologists
• Keepthegardenasweed-freeaspossible.Thiswillhelpthe plants to continue to grow vigorously, and weedsmayharborinsectsthatalsowillattackthevegetables.However, thepresenceofweedsorcompanionplantsmayincreasethenaturalenemypopulation.
• Inspectplantsregularlyforinsectsorinsectdamage.Earlydetectionmeansmoreeffectivecontrolandcanreducethe amount of damage suffered. Particularly in smallgardens,early-detectedcaterpillars,loopers,hornworms,andlargebeetlescanoftenbehandpickedfromplantsanddestroyedbeforetheycauseproblems.
• Treatmost vegetableswith insecticidesonlywhenpestinsectsareobserved;however,treatcertainvegetables,such as cantaloupes, cucumbers, and squash, on apreventivebasistoavoidseriousdamage.
INSECTICIDES Several types of insecticides are available for homegardeners.Table2 lists the insectsmost commonly foundonvegetablesandtheinsecticidesrecommendedtocontrolthem.Thefollowingsectionsdescribe thevarious typesofavailableinsecticides.
Botanical Insecticides (extracted from plants) Neem:Theactive ingredient inNeem,azadirachtin, isderivedfromleavesorseedsofneemtrees.Ithasactivityagainstavarietyofinsectpests.Formanypests,neemactsasarepellent,ratherthanatoxicant.Therefore,itisimportanttoapplyneembeforeaseriousinfestationispresent. Pyrethrum is derived from the flowers of certainchrysanthemums. It causes rapid paralysis and apparent
TABLE 1. Frequency of Insect Damage to Various Vegetables Grown in the Home Garden
Never or Rarely Sometimes Usually or Always
Carrot Asparagus Broccoli
Greenonion Bean Cabbage
Lettuce Pepper Cantaloupe
Pea Spinach Cauliflower
Radish Tomato Cucumber
Eggplant
Potato
Squash
Sweetcorn
2Managing Insects in the Home Vegetable Garden — E-21-W
death, but insects may subsequently recover. Pyrethrumprovidescontrolforupto1dayandismosteffectiveagainstsoft-bodiedinsectssuchasscalesandaphids.
Microbial Insecticides Microbial insecticides available to the home gardenercontainsporesof thebacteriumBacillus thuringiensis (Bt),whichparalyzestheinsect’sgutafterbeingeaten.ABtstraineffectiveagainstmanycaterpillarsissoldasDipel,Javelin,MVP,etc.StrainssoldasM-TrakorNovodorareeffectiveagainsttheColoradopotatobeetle.Microbialinsecticidesarenottoxictobeneficialinsects,humans,orothervertebrates.Spinosadisarelativelynewfermentationproductthathasgoodactivityagainstmostcaterpillars,Coloradopotatobeetles,andthrips.
Manufactured Insecticides Carbaryl (Sevin)isawidelyusedinsecticidewithseveraltradenames.Itiseffectiveonbeetlesandsomecaterpillarsbutdoesnotkillaphids.Carbarylispersistentonplantsfor3-4days,butmaycauseoutbreaksofaphidsandspidermitesbykillingnaturalenemies. Malathion ismoderately effective on a wide range ofinsects,especiallysuckinginsects.Itispersistentonplantsfor2-3days. Several pyrethroid insecticides (bifenthrin, cyfluthrin, esfenvalerate, lambda cyhalothrin, and permethrin) areavailable ffor homeowners to use on vegetables. Theseproductsaresoldunderavarietyoftradenames,sobesuretochecktheactiveingredientonthelabel.Thecropsincluded
TABLE 2. General Garden Pests Commonly Found on Vegetables and Recommended Insecticides to Control Them.
3 Managing Insects in the Home Vegetable Garden — E-21-W
onthelabelvary,sobesurethatthecropyouaretreatingislistedbeforeyouspray.Allofthepyrethroidsareextremelyeffective insecticides that will provide up to 7-10 days ofcontrolofawidevarietyofpests.TheywilleffectivelycontrolColoradopotatobeetlesthatareresistanttoinsecticidessuchasSevin.Pyrethroidsareextremelytoxictofish,socautionshouldbeusedaroundbodiesofwater.Pyrethroidsarealsotoxictohoneybees.Inorganic Insecticides (oils and soaps) Horticulturaloilsworkonlyoncontactandhavenoresidualactivity.Commerciallyavailableinsecticidalsoaps,whicharemadefromnaturallyoccurringfattyacids,helpcontrolaphids,leafhoppers,mites,scales,andwhiteflies.Likeoils,soapsonlycontrolthoseorganismsonwhichthespraylands.
Some Notes About Insecticides• Althoughmostinsecticidesavailableforuseinthehomegardenarerelativelysafetouse,theyareallPOISONS andshouldbeusedwiththeutmostcare.Carefully read and follow all precautions on the insecticide label.Table3liststhenumberofdaysyoumustwaitaftertreatmentbeforeharvesting thevegetables.Vegetablesshouldbethoroughlywashedbeforetheyareeatenorcooked.
• Sometimes using an insecticide will increase insectproblems.Forexample,overuseofcarbarylonsomecropscanincreaseproblemswithaphids,mites,andwhitefliesbecauseitkillsthenaturalenemiesthateatthosepests,butdoesnotkillthepeststhemselves.
TABLE 3. Harvest Restrictions in DAYS for Common Vegetable Insecticides
4Managing Insects in the Home Vegetable Garden — E-21-W
• When properly applied, sprays and dusts should giveadequatecontrolofinsects.Plantsneedonlyalightcoatingofdust,butitmustbeonboththeupperandlowerleafsurfaces.Becauseofthis,shaker-candustersusuallydonotdoanadequatejob.Squeezeorplungerdustersprobablyarebetter,asareaerosoldusters if keptagitatedwhiledusting.Dustswillusuallybemoreexpensiveperounceofactiveingredientthansprayformulations.
•Whenspraying,bothupperandlowerleafsurfacesmustbetreated.Sprayerpressuremustbesufficienttorollleavesover.Aerosol cans of insecticide are not recommendedexcepttotreatindividualplantsorverysmallgardens.Unlessotherwisenotedonthemateriallabel,agallonofspraywillcoverapproximately500squarefeetor200feetofrow.
ORGANIC GARDENING Although properly used insecticides do not adverselyaffecthumanhealth,somegardenersnonethelesschoosetogrowtheirvegetablesorganically.“Organic”meansthatnochemicalfertilizersorsyntheticpesticidescanbeused.Theuseofcertainpesticides,suchasBacillus thuringiensis,oilsandsoaps,pyrethrum,spinosad,andneemisallowed.Forthemostpart,vegetablescanbegrownforhomeconsumptionwithouttheuseofthechemicalinsecticides.Thismay,however,requiremoreworkthanifinsecticideswereused.
GENERAL GARDEN PESTS
White Grubs Severalspeciesofwhitegrubs feedon rootsorotherundergroundpartsofmost vegetables.Damagegenerallyconsists of root pruning, surface scars, or round gouges.Grubsaremostlyaproblem ingardens thatweresod thepreviousyear.Gardenswithgrassyweedsareattractivetobeetleswhentheylayeggs.Assoilispreparedforplantinginthespring,itshouldbecheckedforthepresenceofgrubs.
Christine
Brian
Whitegrubs
Wireworms Wirewormscan feedon seedsandseedlingsof corn,beans,andpeas,causingwiltingand/ordeathoftheyoungplant.Wirewormsfeedontheedibleportionsofpotato,sweetpotato, radish, carrot, rutabaga, and turnips. The roots ofcabbage,cucumber, tomato,onion,watermelon,andothercropsarealsoattacked,reducingvigororkillingtheplants.Despitethelonglistofhostplants,wirewormsarerarelyaproblemingardens.Wirewormsaremore likely to infestagardenifitweresodlastyearorhadlotsofgrassyweedspresent.
Japanese Beetle InsomepartsofIndiana,theJapanesebeetleisthemostseriousinsectproblemthatmanyhomeownershavetocontendwith. Japanese beetles can be present in extremely highnumbers,arevoraciousfeedersonawidevarietyofplants,
6Managing Insects in the Home Vegetable Garden — E-21-W
MANAGING INSECTS ON SPECIFIC CROPS
Asparagus The asparagus beetle and the spotted asparagus beetlearebothfoundonasparagus,butonlytheasparagusbeetleisaseriouspest.Adultasparagusbeetlesare1/4inchlong,blue-black,withcreamyyellowspotswithredborderson thewings.Adultspottedasparagusbeetlesareslightlylarger,arereddish-orange,andhaveblackantennae,eyes,andundersides.Eachwingcoverhassixdistinctblackspots.Thesoft-bodiedlarvaeoftheasparagusbeetlereach3/8inchlongandaregraywithblackheads.Adultasparagusbeetlesattackthetenderbudsnearasparagustipsassoonastheshootspushabovethesoilinthespring.Theadultsalsofeedonthefoliage.Larvaeoftheasparagusbeetlefeedonthestemsandleaves,butthelarvaeofthespottedasparagusbeetlefeedonlyontheberries. Destroyingcropresiduefromthepreviousyeareliminatesoverwinteringsitesfortheadults.Hand-pickingadultscanalsobeuseful.Chemicalcontrolisusuallyquiteeffectiveandmaybejustifiedifthereareseveralbeetlesorlarvaepercrown,orifplantsarelosingtheirleaves.
MichiganStateUniv.
MichiganStateUniv.
Asparagusbeetleadultandlarva
MichiganStateUniv.
Spottedasparagusbeetle
Beans Green,wax,broad,andlimabeansgrowninthevegetablegardenareallattackedbyseveralinsects,butthedamageoftencanbetolerated.Thefirstinsectthatwillattackbeansistheseedcorn maggot.Theadultformisaflythatisslightlysmaller thanahouse fly.Thedamaging form is the larva,whichisawhite,leglessmaggotthatburrowsintoseedsandseedlings,causingpoorseedgerminationandemergence,and/or stemswithout leaves.Damage can be reduced byplantingseedsshallowandwhensoiltemperaturesarewarm
Potato leafhopper isfrequentlyapestonbeans.Adultsareabout1/8 inch long,brightgreen,andwedge-shaped.Bothadultsandnymphsfeedbysuckingplantjuices.Toxinsintheleafhopper’ssalivacauseplantstostuntandleavestoyellowandturnbrown,aconditioncalled“hopperburn.”Leafhoppersoftenwillmoveoutofalfalfa intoothercropswhenalfalfaiscut.Leafhoppersshouldbecontrolledbeforehopperburnsymptomsappear.
J.Obermeyer
J.Obermeyer
J.Obermeyer
Potatoleafhopperadult,nymphs,anddamage
Flea beetlesmaychewsmallholesinbeanleaves.Thisdamagewillusuallybeworseinweedygardens.Thedamageis usually only important on seedling plants. Carbaryl willprovideadequatecontrolifneeded.
about28days)thattheyarenotusuallyaffectedbyinsects,otherthanpossiblyafewcabbagemaggotsfeedingontheroots.Turnipsgrownfortherootsarealsounlikelytohaveanyseriousinsectproblems,otherthanrootmaggots. The first insect problem that will occur on crucifers isthecabbage maggot.Theadultfly,whichisslightlysmallerthanahousefly,emergesinlateAprilorearlyMay.Theylaywhiteeggsatthebasesofnewlysetplants.Theeggshatchintoleglessmaggotsthatmigrateandtunnelintotheroots.Theycausetheplantstoappearsickly,offcolor,orstunted,andmaycausethemtodie.Injuryisusuallymoresevereincool,wetconditions.Forthehomegardener,chemicalcontrolisusuallynoteffective.Anothergoodideaistoplantafewmoreplantsthanneeded,incaseafewarelosttocabbagemaggots.Fliesareattractedtodecayingorganicmatter,soexcessiveuseofmanureshouldbeavoided.
C.E
astman
Cabbagemaggotdamage
Flea beetles are almost always a pest of crucifers.Carbarylwill usuallyprovidesuitablecontrol.Aphidsmayattackallthecrucifers,aswell.Thenumberofaphidsmaybereducedbydestroyingcropresiduewhenthegrowingseasonhasendedandbyencouragingnaturalenemiessuchasladybeetles.Naturalenemiescanbeconservedifuseofchemicalinsecticidesiskepttoaminimum.
8Managing Insects in the Home Vegetable Garden — E-21-W
Asmostgardenersknow,themostseriousinsectproblemoncrucifersisthecaterpillars.Thereareactuallythreedifferentspecies of caterpillars that are serious pests of crucifers.Diamondback moth larvaearesmall(1/2inch),cigar-shapedgreencaterpillars thatwriggle rapidlywhen touched.Theypupateinlittlesilkencasesgluedtotheundersidesofleaves.Eachlarvadoesnotdoagreatdealofdamage,buttheycanoccurinextremelyhighnumbers.
caterpillars and treated when necessary, or Bt should beappliedonaweeklybasis.Thepyrethroid insecticidesarealsoquiteeffective.
Solanaceous Crops (Tomatoes, potatoes, peppers, eggplant) Solanaceous crops are attacked by a wide variety ofinsects.Severalofthesepestscanbequitesevereanddifficulttocontrol,asisindicatedinTable1.Thesecropsareoftendifficulttogrowsuccessfullywithoutusinginsecticides. ThemostnotoriousofallthepestsofsolanaceouscropsistheColorado potato beetle.Thisinsectfeedsonallfourtypesofsolanaceouscropsinboththelarvalandadultstages.Theadult isayellowbeetleabout1/2 inchlongwitheachwingcoverbearingfiveblackstripes.The larva is reddishwithablackheadandlegsand2rowsofblackspotsalongeachside.Overwinteringadultsfrequentlybeginfeedingonpotatofoliageassoonasitisaboveground.Bothadultsandlarvaefeedonalltheleaftissueexceptforthemainleafveinandstems.Therearetwogenerationsperyear.Theinstarguideonpage9willhelp thehomegardenerknowwhichinstarsarepresent.The larger instarswill consumemuchmorefoliageeachdayandarealsomuchmoredifficulttokillwithinsecticides.Therefore,itisimportanttomakeinsecticideapplicationswhenthelarvaearesmall(1stor2ndinstars).Inmanyareas,Coloradopotatobeetlesareresistanttomostinsecticidesavailabletohomeowners. Bacillus thuringiensisinsecticidesspecificallyforpotatobeetlescanbeeffectiveifappliedwhenlarvaearesmall(1stor2ndinstar).Otheravailablealternativetoinsecticidesinclude
Thecabbage looperdoesnotoverwinterinIndiana,butflieshereeachJune.Thelarvaearelightgreen,and,whentheycrawl,theymakeacharacteristicloopinthemiddleoftheirbody.Thesecondgeneration,whichoccursinAugustandSeptember,isthemostserious. Allthesecaterpillarsfeedontheleavesandcanreducetheplantgrowth.Themostseriousdamageistotheportionsofplantsthataretobeconsumed.Fortunately,goodcontrolcanbeachievedwithvariousformulationsofBacillus thuringiensis.Thismaterialisverysafeandwillnotharmbeneficialinsects.It ismuchmore effective on the young larvae.Therefore,plantsshouldbeinspectedonceortwiceperweekforyoung
handpickingadultsofftheplantsanddestroyingthembeforetheybegintolaytheirorange-redeggsontheundersidesoftheleaves.Damagecanalsobereducedbyapplyinga4-6inchlayerofstrawmulchonbothsidesofthepotatorowrightafterhilling. Flea beetleswillattackallofthesolanaceouscrops,butcanbeparticularlydamagingtoeggplant.Fleabeetlesaresmall,hard-shelledinsects,sonamedbecausetheirenlargedhind legs allow them to jump like fleas from plants whendisturbed.Theirdamageisunusualinappearance.Theyfeedbychewingasmallholeinaleaf,movingashortdistance,thenchewinganotherhole,andsoon.Mosthealthyplantscantolerateaconsiderableamountoffleabeetledamage,andcontrolisobtainedeasilywithanumberofcommongardeninsecticides.RefertoExtensionpublicationE-74,Flea Beetles,foradditionalinformation.
Univ.W
isconsin
Fleabeetlesanddamage
Univ.W
isconsin
Thepotato leafhopperdescribed in thebeansectionisalsoapestofpotato,doingdamagesimilartothatdonetobeans.Leafhoppers cancausesubstantial yield lossatrelativelylowdensities.Treatmentisjustifiedifthereismorethanonenymphpertenleaves.Severalspeciesofaphidswillattacksolanaceouscrops.Fortunately,potatoesandtomatoescantolerateaconsiderableamountof feedingwithoutanyeffect on yield. However, aphids feeding on peppers cantransmitseveralviraldiseasesthatarequitedetrimentaltopepperplants.Peppers,therefore,shouldbekeptrelativelyfreeofaphids.
The tomato fruitworm (also thecorn earworm) is alate-seasonpest(August-September)thatboresintothefruit.Thelarvaevaryconsiderablyincolorfromlightgreentotan,brown,pink,maroon,ornearlyblack,withlightanddarkstripesrunninglengthwiseonthebody.Theyreachalengthofabout11/2inches.Theymaybecontrolledwithinsecticides,butusuallythedamagecanbetoleratedandthedamagedfruitsimplydiscarded.
10Managing Insects in the Home Vegetable Garden — E-21-W
Vine Crops (Cucumbers, melons, pumpkins, squash) Seedcorn maggots are closely related to cabbagemaggotsandwillattackallthevinecrops.Damageismoreserious if thecropsareplanted intoheavilymanuredsoil.Damageisalsomoresevereincoolweather.Plantswillgrowmorevigorouslyiftheyareplantedaslateaspossible.Also,plantingafewextraseedsperhillwillreducetheeffectofanyseedcornmaggotinjury.
G.B
rust
G.B
rust
Seedcornmaggotanddamage
Probably themost serious insect pests of vine crops,especiallycucumbersandcantaloupes,arethespottedandstriped cucumber beetles.Thespottedcucumberbeetleisgreenishyellowandhas12blackspotsonthewingcover.Thestripedcucumberisyellowwiththreeblacklinesrunningthelengthofthebody.Thelegsandundersidesarealsoblack.Thebeetlesfeedonstemsandleaves,butthemostimportantdamage they do is to transmit a bacterium that causes adiseasecalledbacterialwiltofcucurbits.Thediseaseplugsup the liquid-conducting tubeswithin theplantand resultsinthesudden,severe,andpermanentwiltofasingleplantrunnerortheentireplant. The onlyway to prevent the disease is to control thebeetles.Whentheplantsaresmall, theycanbeprotectedfrombeetlefeedingbycoveringtheplantswithasmallmeshmaterialsuchasabridalveilsupportedonastickwithdirtsealingtheedgesontheground.Ofcourse,whentheplantsstarttobloom,theclothmustberemovedtoallowbeestopollinatetheplants.Theothercontroloptionistoprotecttheplantswithaninsecticidewhenthebeetlesarepresent.
BENEFICIAL ARTHROPODS Onlyaverysmallpercentageoftheinsectsthatoccurin Indianaarepests,andonlya fewof thesearepestsofvegetables. Most insects are so innocuous that they areseldomnoticed.Manyprovidefoodforlargeranimals,helpbreakdowndecayingplantsandanimals,etc. Otherinsectsprovidedirectbenefitforgardeners.Anumberofinsectsandotherarthropodsarepredators;thatis,theyeatotherinsectandmitepests.Predatorsincludespiders,adultandimmatureladybeetles,adultandimmaturelacewings,preyingmantids,somestinkbugs,andgroundbeetles.Otherinsectsactasparasitesonpestinsects.Theseincludeanumberofspeciesofwaspsandflies,whichlayeggsinoronthehostinsect.Thus,itisimportanttoconserveasmanypredatorsandparasitesaspossible.Often theywill control thepestspecieswellenoughthatadditionalcontrolisnotnecessary.Agoodmethodforconservingbeneficialinsectsistosprayinsecticidesonlywhennecessaryandtochooseinsecticidesthatareleasttoxictothebeneficialinsectswheneverpossible. Oneofthemostnotablebeneficialinsectsisthehoneybee.