Pesticides

Pesticides

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.

Pesticide Classification

• Pesticides are commonly classified several ways:

• Chemical class -- Increasingly diverse

• Target Organism

• Mode of Action

• Application timing or usage

Pesticides Classified by Target

Target classification may also specify growth stages

• Ovicides – Eggs

• Larvicides – Larvae

• Adulticides -- Adults

Mode of Action Examples

• 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

Classification by Timing

• 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

Benefits of Pesticides in IPM

• Inexpensive

• Greater control confidence

• Effective and rapid

• Therapeutic

• Management efficiency

• Can enable other management practices

Costs of Pesticides in IPM

• 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

Role of Pesticides in IPM

• 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

Pesticide Strategy Vs. Tactic

• As a group, pesticides may be therapeutic or preventative, broad or narrow spectrum, fast or slow acting, long or short lived, etc.

• As individuals, each pesticide occupies one point on this multidimensional continuum.

• The key is to consider each individual pesticide as a separate tactic in an overall IPM plan.

The Selectivity Concept

• Key concept in pesticide usage in IPM

• Pesticides often classified as “selective” or “non-selective”

• Meaning of these terms in common usage is context-dependent (weeds vs. insects)

• More formally, there are two types of selectivity – Physiological and Ecological

Physiological Selectivity

• Relative toxicity of pesticides under controlled application conditions

• Species-specific susceptibility to a pesticide.

• Measured as a ratio of LD50’s of non-target/target species (cf. table handout)
• Assumes all individuals & species equally dosed.

• Three general methods:

• Residues (cf. handout)
• Topical application to individuals
• Before/after assessment of field populations

Ecological Selectivity

• Differential mortality based on pesticide use

• Formulation (e.g. granules result in more mortality on soil pests than on foliar NE’s)
• Placement (e.g. spot sprays, seed treatments, wicks, in-furrow).
• Timing (e.g. pre vs. post-emergent applications, diurnal timing for bees)
• Dosage – Reduced dosage usually used in conjunction with one of those above

Uses of Selectivity in IPM

• Mammalian toxicity of decreasing significance except in urban/structural IPM

• Insecticides – Physiological selectivity favored (target & non-target intermingled)

• Herbicides – Historically favored ecological selectivity

• Bactericides/Fungicides – Non-selective pesticides usually favored.

Types of Pesticides

• Your book identifies two kinds (pp. 250 – 257)

• Traditional Toxic Chemicals

• Inorganic
• Organic (Synthetic)

• Biopesticides

• Living Systems (Microbial pesticides)
• Fermentation Products
• Botanical Pesticides
• Transgenic (Plant Incorporated Pesticides) – cover under host plant resistance