Pesticides are substances used to control pests and are classified in several ways, including by chemical class, target organism, and mode of action. Common pesticides target weeds, insects, fungi, or other pests. They work through various modes of action such as inhibiting amino acid biosynthesis, lipid biosynthesis, or photosynthesis. Proper application timing and techniques are important to maximize effectiveness while minimizing harm to non-target species. Pesticide resistance can develop if pest populations are not properly managed.

2.  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.

3. Pesticides are commonly classified several
ways:
 Chemical class -- Increasingly diverse
 Target Organism
 Mode of Action
 Application timing or usage

4. Term Target Term Target
1. 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

5.  Ovicides – Eggs
 Larvicides – Larvae
 Adulticides -- Adults

6.  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

7. 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 sequence
Perennial Crops
 Dormant -- Applied during winter dormancy
 Bud Break -- Applied as dormancy is broken
Harvest-Related Timing
 Pre-Harvest -- Just before crop is harvested
 Post-Harvest -- After crop is harvested

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

9.  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

10.  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

12.  Better understanding of how herbicides
perform
 Improve herbicides performance
 Diagnosing herbicide injury
 Prevent and manage herbicide resistance

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

14.  Use herbicides to achieve your goal
• Reduce the impact of invasive species
• Secure the presence of targeted species
But not all herbicides are equal!

15.  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

16. Foliar Contact
(Gramoxone)
Root Contact
(Treflan)
Phloem
(Roundup)
Xylem
(Spike)
Xylem and
Phloem
(Banvel, Tordon)

17. Commercial Products (Roundup, Durango)
Mode of Action
(Amino Acid Biosynthesis Inhibitors)
Site of Action (EPSPS inhibitor)
Chemical Family (Glyicines)
Active Ingredient (Glyphosate)

18.  Sequence of events from
absorption of the herbicide
into the plant until the plant
dies

19. Contact
Absorption
Movement
Site of
Action
Herbicide Mode of Action
Toxicity
CO2 + H2O Sugar + O2

20. 1) Plant Growth Regulators
2) Amino Acid Biosysthesis Inhibitors
3) Lipid Biosynthesis Inhibitors
4) Cell Division Inhibitors
5) Photosynthesis Inhibitors
6) Cell Membrane Disrupters
7) Pigment Inhibitors
8) Unknown mode of action

21.  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

22.  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

23. Chemical Family Common Name Trade Name
Phenoxy acetic acids 2,4-D 2,4-D, Campaign,
Crossbow,
Landmaster BW,
others
2,4-DB Butyrac
MCPA MCPA, others
Benzoic acid dicamba Banvel, Clarity
pyridines clopyralid Curtail, Transline
fluroxypyr Starane
picloram Tordon
Examples of PGR

24. Parallel veination due to 2,4-D
Photo: HMOA and Crop Injury Symptoms.
Univ. of Minnesota Extension


25. Leaf cupping caused by dicamba
Photo: HMOA and Crop Injury Symptoms.
Univ. of Minnesota Extension


26. Puckered soybeans from Tordon
Photo: Kansas State University Extension

27. Tordon runoff into soybean fieldTordon runoff into soybean field
Photo: Kansas State University Extension

28.  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+)

29. Chemical Family Common Name Trade Name
Sulfonylureas chlorsulfuron Glean, Telar
thifensulfuron Harmony GT
nicosulfuron Accent
Imidazolinones imazamethabenz Assert
imazapic Plateau
imazamox Raptor
Amino acid derivates glyphopste Roundup, Glyphomax,
Rodeo, and others
Examples of Amino Acid Synthesis Inhibitors

30.  Amber: Triasulfuron
 Cimarron, Escort: Metsulfuron
 Journey: Imazapic + glyphosate:

31. Chlorosis of New Growth on Tansy Mustard

32. Plateau Injury Symptoms
Stunting
Chlorosis of
youngest tissue

33.  Tightly adsorbed and inactive in soil
 Phloem translocated
 Inhibits EPSP enzyme responsible for
production of aromatic amino acids
phenylalinine, tyrosine and tryptophan
 Very nontoxic

34. Gradual Death from Roundup Treatment

35. Glyphosate (Roundup) Injuries
chlorosis
shortened
internodes
stem proliferation

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

38.  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

39.  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

40.  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

41. Injury from PSII herbicide
Note the interveinal chlorosis

42.  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

43.  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

44. Rapid browning (necrosis)
of plant tissue

45. Paraquat injury on corn leaves

46.  Better understanding of how herbicides
perform
 Improve herbicides performance
 Diagnosing herbicide injury
 Prevent and manage herbicide resistance

47. 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

48. 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

49. Where do Resistant Weeds
Come From?
One in one million, billion, trillion….?
It’s all about selection…..

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