pesticides

Pesticides Defined: Any substance or mixture of substances, intended for preventing, destroying, or mitigating any pest, or intended for use as a plant growth regulator, defoliant or desiccant. (FIFRA)

Technically includes biocontrols and plants bred for pest resistance. Common usage excludes these.

Pesticides are commonly classified several ways:

Chemical class -- Increasingly diverse Target Organism Mode of Action Application timing or usage

Term Target Term Target1. Algaecide Algae 2. Avicide Birds

3. Bactericide Bacteria 4. Defoliant Crop Foliage

4. Desiccant Crop Plants 5. Fungicide Fungi

6. Herbicide Plants (weeds) 7. Insecticide Insects

8. Miticide Mites 9. Molluscicide Molluscs

10. Nematicide Nematodes 11. Plant Growth Reg.

Crop Plants

12. Rodenticide Rodents 13. Piscicide Fish

14. Lampricide Lamprey 15. Wood Preservative

Wood Destroying

Pests

Ovicides – Eggs

Larvicides – Larvae

Adulticides -- Adults

Broad Spectrum -- Kills broad range of pests, usually refers to insecticides, fungicides, and bactericides

Contact Poison -- Kills by contacting pest Disinfectant (Eradicant) -- Effective against pathogen that has already

infected the crop Germination Inhibitor -- Inhibits germination of weed seeds, fungus

spores, bacterial spores. Nonselective -- Kills broad range of pests and/or crop plants, usually

used in reference to herbicides Nerve Poison -- Interferes with nervous system function Protectants -- Protects crop if applied before pathogens infect the crop Repellents -- Repels pest from crop or interferes with pest’s ability to

locate crop Systemic -- Absorbed and translocated throughout the plant to provide

protection Stomach Poison -- Kills after ingestion by an animal

Annual Crops Seed Treatment -- Pesticide coats or is absorbed into the seed. Pre-Plant -- Pesticide applied any time before planting At-Planting -- Pesticide applied during the planting operation In-Furrow -- In the planting row, direct contact with crop seed Side-Dress -- Next to the row, no direct contact with crop seed Broadcast -- Distributed over the soil surface. Pre-Emergent -- Before the crop has emerged from the ground Post-Emergent -- After the crop has emerged from the ground Lay-By -- Final operation before harvest sequencePerennial Crops Dormant -- Applied during winter dormancy Bud Break -- Applied as dormancy is brokenHarvest-Related Timing Pre-Harvest -- Just before crop is harvested Post-Harvest -- After crop is harvested

Inexpensive Greater control confidence Effective and rapid Therapeutic Management efficiency Can enable other management practices

Greater human health threat Greater environmental cost Detrimental effects on non-target species

• Those useful in the CPS• Those useful outside the CPS• Those with no established uses

Interferes with other aspects of IPM• Secondary pests• Re-entry Intervals & scouting• Limits other control options

Less sustainable

Pest complex – Some require pesticides• Multiple, simultaneous species in same group• At least one species that causes excessive

damage at low density• Important species new/poorly understood• Key pest(s) lacking control alternatives• Key pest(s) especially vulnerable to pesticide

placement/timing

Better understanding of how herbicides perform

Improve herbicides performance Diagnosing herbicide injury Prevent and manage herbicide resistance

Photosynthesis (food) Pigments (energy/light capture) Respiration (energy) Amino acids (proteins/growth) Lipids (cell membranes) Mitosis (cell division)

Use herbicides to achieve your goal • Reduce the impact of invasive species• Secure the presence of targeted species

But not all herbicides are equal!

Selective: controls or suppresses one species of plant without seriously affecting the growth of another plant species 2,4-D

Nonselective: control plants regardless of species Roundup

Foliar Contact(Gramoxone)

Root Contact(Treflan)

Phloem (Roundup)

Xylem(Spike)

Xylem and Phloem(Banvel, Tordon)

Commercial Products (Roundup, Durango)

Mode of Action (Amino Acid Biosynthesis Inhibitors)

Site of Action (EPSPS inhibitor)

Chemical Family (Glyicines)

Active Ingredient (Glyphosate)

Sequence of events from absorption of the herbicide into the plant until the plant dies

Contact

AbsorptionMovement

Site of Action

Herbicide Mode of Action

Toxicity

CO2 + H2O Sugar + O2

1) Plant Growth Regulators2) Amino Acid Biosysthesis Inhibitors3) Lipid Biosynthesis Inhibitors4) Cell Division Inhibitors5) Photosynthesis Inhibitors6) Cell Membrane Disrupters7) Pigment Inhibitors8) Unknown mode of action

Synthetic auxins (regulate plant growth) Affect several plant processes such as

cell division, cell enlargement, protein synthesis and respiration

Act by upsetting the normal hormonal balance in plants

Herbicide uptake is primarily through the foliage but root uptake is possible

Translocate in both xylem and phloem Effective on perennial and annual

broadleaf weeds Selectively kill broadleaf plants

• Injury may occur in grasses

Chemical Family Common Name Trade NamePhenoxy acetic acids 2,4-D 2,4-D, Campaign,

Crossbow, Landmaster BW, others

2,4-DB ButyracMCPA MCPA, others

Benzoic acid dicamba Banvel, Claritypyridines clopyralid Curtail, Transline

fluroxypyr Staranepicloram Tordon

Examples of PGR

Parallel veination due to 2,4-D

Photo: HMOA and Crop Injury Symptoms.

Univ. of Minnesota Extension

Leaf cupping caused by dicamba

Photo: HMOA and Crop Injury Symptoms.

Univ. of Minnesota Extension

Puckered soybeans from Tordon

Photo: Kansas State University Extension

Tordon runoff into soybean fieldTordon runoff into soybean field

Photo: Kansas State University Extension

Prevent synthesis of certain amino acids produced by plants but not animals

Excellent foliar and root absorption Broad weed spectrum Translocates to shoot and root new growth in

both xylem and phloem Plants stop growing shortly after application Plant death may be slow (10 days+)

Chemical Family Common Name Trade NameSulfonylureas chlorsulfuron Glean, Telar

thifensulfuron Harmony GTnicosulfuron Accent

Imidazolinones imazamethabenz Assertimazapic Plateauimazamox Raptor

Amino acid derivates glyphopste Roundup, Glyphomax, Rodeo, and others

Examples of Amino Acid Synthesis Inhibitors

Amber: Triasulfuron Cimarron, Escort: Metsulfuron Journey: Imazapic + glyphosate:

Chlorosis of New Growth on Tansy Mustard

Plateau Injury Symptoms

Stunting

Chlorosis ofyoungest tissue

Tightly adsorbed and inactive in soil Phloem translocated Inhibits EPSP enzyme responsible for

production of aromatic amino acids phenylalinine, tyrosine and tryptophan

Very nontoxic

Gradual Death from Roundup Treatment

Glyphosate (Roundup) Injuries

chlorosisshortened internodes

stem proliferation

Mimics 2,4-D and other hormone-like herbicides

Control annual or perennial grasses or broadleaves Shut down the photosynthetic process Slow starvation of the plant However, the plant experiences a more rapid death

be due to the production of secondary toxic substances

Injury symptoms: yellowing (chlorosis) of leaf tissue followed by death (necrosis) of the tissue

Controls big sage, shinnery and other oaks, tarbush and creosote bush

Sagebrush thinning and brush sculpting programs

Rangeland, pastures, clearings for wildlife and other non-cropland areas

tebuthiuron

Injury symptoms: Only occur after the cotyledons and first leaves emerge

(do not prevent seedlings from germinating or emerging) yellowing (chlorosis) of leaf tissue followed by death

(necrosis) of the tissue Older and larger leaves affected first: they take up

more of the herbicide-water solution as they are the primary photosynthetic tissue of the plant

Injury from PSII herbicideNote the interveinal chlorosis

Postemergence contact herbicides Little soil activity Activated by exposure to sunlight to form oxygen

compounds such as hydrogen peroxide These oxygen compounds destroy plant tissue by

rupturing plant cell membranes Perennial weeds usually regrow because there is

no herbicide movement to underground root or shoot systems

Controls weeds in just 24 to 48 hours

Broad-spectrum and non-selective control of grasses, broadleaf weeds and sedges

Cheatgrass, kochia, Russian thistle, annual mustards

No residual effect

Rapid browning (necrosis) of plant tissue

Paraquat injury on corn leaves

Better understanding of how herbicides perform

Improve herbicides performance Diagnosing herbicide injury Prevent and manage herbicide resistance

Herbicide Resistance is NOT due to:

1. Sprayer skips or plugged nozzles

2. Weather problems that cause poor control

3. Plants that are ‘naturally tolerant’ to the herbicide

4. Genetic changes caused by the herbicide

Herbicide Resistance is:The ability of a plant to survive and reproduce after treatment with a dose of herbicide that would normally kill the plant

Banvel-resistant kochia

Where do Resistant Weeds Come From?

One in one million, billion, trillion….?

It’s all about selection…..

Selection intensity• Herbicide efficacy • Length of soil residual period• Number of herbicide applications / year