Pesticides Flashcards
What is a pesticide?
Any substance or mixture intended to prevent, destroy, repel, and mitigate any pest and intended for use as a plant regulator, defoliant or desiccant
How can pesticides be categorized?
based on intended purpose
based on application
based on relation to target pest (mode of action)
based on chemistry
What are pesticide categories based on intended purpose?
insecticides (can be for a specific species or point in lifecycle)
herbicides (most widely used)
fungicides
rodenticides (mostly for food storage)
What are pesticide categories based on application?
How? air application - plane, tractor, human plastic covered broadcast vs. targeted When? same time as planting (treated seed or next to seed) specific stages of growth
What are pesticide categories based on mode of action?
contact - must contact pest, some more stable than others that require re-application, can remain on plant until insect lands (lots of fungicides and insecticides)
systemic - translocated with plant tissue, relies on persistence, pest ingests tissue and (active) pesticide
What makes a product a pesticide?
intent, claims, composition, knowledge that it will be used as a pesticide
What are the benefits of pesticide use?
higher yields
improved quality
reduced labor, machinery, fuel
How has pesticide use changed over time?
boom of use started in 1960s - 1980s - increased planted acres + increased treated acres
downward trend since 1980 - improved application methods and better ingredients - need less
*many old pesticides still used
*USDA no longer tracks pesticide/fertilizer use
What are the drivers of changes in pesticide use?
changes in pest pressures
environmental and weather conditions
crop acreages have changed
ag practices
cost-effectiveness (value of damage reductions vs. control costs)
regulations
access to experts
tech innovations
new products that decrease per acre application rate
adoption of GE crops
price of crops, pesticides, other practices
IPM
farm and energy policy
risk and uncertainty (responsive vs. preventative - monitoring costs)
What are different classes of pesticides based on chemistry?
chlorinated hydrocarbons organophosphates carbamates triazine herbicides phenoxy herbicides botanicals - pyrethroids,
What are chlorinated hydrocarbons (organochlorines)?
insecticides - mostly off the market now
act as nerve agents
widely used in 1940s-1960s
What are examples of chlorinated hydrocarbons?
DDT, aldrin, dieldrin, heptachlor, lindane
How do chlorinated hydrocarbons work?
concentrate in the fatty tissue and bioaccumulate
act as nerve agents
disrupt calcium mobilization
What are concerns with chlorinated hydrocarbons?
very persistent in the environment
toxic to non-target organisms - fish especially (lindane)
bioaccumulation - concentration in food chain, harm predatory birds
What are organophosphates?
insecticides - most commonly used
replaced many organochlorines in the 1970s
many are restricted use
What are examples of organophosphates?
diazinon, malathion, methyl parathion, terbufos
What are concerns with organophosphates?
can be extremely toxic to fish and birds
generally higher mammalian toxicity
better - less persistent in environment, don’t bioaccumulate
How do organophosphates work?
cholinesterase inhibitors
increase toxicity by all routes of exposure
What are carbamates?
insecticides - many are systemic, some regulators of plant growth
subclass - thio- and dithiocarbamates - many common herbicides
act as acetylcholinesterase inhibitors
What are subclasses of carbamates?
aldicarb - one of most toxic ever approved
carbaryl - one of most widely used (residential)
carbofuran - banned in granular form
thio and dithiocarbamates - include a sulfur molecule, includes butylate, EPTC
What are concerns of carbamates?
mobile in soil and groundwater (aldicarb)
extreme acute toxicity in mammals (aldicarb)
toxic to birds
better - low-moderate environmental persistence; thio and dithios have lower toxicity
What are triazine herbicides?
photosynthetic inhibitors
among most widely used
subject to special review - stability in water
What are examples of triazine herbicides?
atrazine, cyanazine, metribuzin
What are phenoxy herbicides?
very widely used (farm and home)
act as synthetic plant hormones (auxin-like)
What are examples of phenoxy herbicides?
2,4-D and 2,4,5-T
What are botanical pesticides?
come from other plants or synthetics
ex) pyrethroids, rotenone (from bean), strychnine (poison), nicotinoids (from tobacco) - neonicotinoids, imidicloprid, synthetics
What are pyrethroids
come from chrysanthemum or synthetic (lots) insecticides ex) Ambush have higher insect:mammal selectivity shorter persistence
What factors effect pesticide toxicity or negative impacts?
have a potential effect on other organisms (beyond toxicity)
also depends on: stability or persistence, form, solubility and transport potential, breakdown products
How do pesticides move?
laterally - with runoff or sediment
drift from spray
leach into saturated zones
by wind or rain (into non-ag areas)
What is selectivity?
the differential sensitivity of the organism to the pesticide
ex) kills only certain type of plant or certain stage of life
What is resistance?
“inherited ability of the plant to survive and reproduce following exposure to a herbicide dose normally lethal to the wild type”
How many plants/insects have developed resistance so far?
500+ insects
100 dicots
70 monocots
What are major issues with pesticides?
resistance - norm not the exception
non-target organism impacts - kill beneficial insects
on-site this can cause outbreak of secondary pest
off-site impacts birds, bees, fish, humans
survival and reproduction in face of resistance
How does survival and reproduction happen?
self-pollinating weed that survives yields viable seeds with a heritable resistance - often single site mutation
insect that survives needs to find a resistant mate to reproduce successfully
What is refugia?
maintaining a susceptible population as part of management
How does resistance develop?
repeated production of single or few crops
repeated application of same or similar chemicals
both of these are common characteristics of production system currently
eventually, continued application favors resistant members
What is selection intensity?
a function of effectiveness, frequency, duration
What are types of resistance?
metabolic - detox the pesticide
target site - alteration to binding site
delayed penetration (no longer active) - insect or plant
behavioral - avoidance for example
What is dose response?
survival percentage to the application rate, 100% isn’t the norm
