Pest Identification and Control
What this domain tests
Identification items describe a plant, insect, or symptom and ask you to name the pest group and pick the right tactic and timing.
Weeds
- Grasses (monocots) have parallel veins, hollow round stems, and ligules; broadleaves have net veins and two cotyledons.
- Sedges resemble grasses but have triangular stems and three-ranked leaves - "sedges have edges." Yellow and purple nutsedge are perennials that regrow from tubers and are poorly controlled by grass herbicides.
- Match timing to the chemistry: preemergence herbicides must be on before weeds emerge and usually need rain or irrigation to activate; postemergence products need actively growing, unstressed weeds.
Insects
- Mouthparts drive product choice: chewing pests (caterpillars, beetles) are targets of stomach poisons; piercing-sucking pests (stink bugs, aphids, thrips) need contact or systemic activity.
- Scout with the tool named in state recommendations - sweep net in soybean, drop cloth or beat sheet in cotton, soil cores for nematodes - and treat at the economic threshold.
Disease and resistance
- Separate biotic disease (spreading lesions, sporulation, patchy patterns) from abiotic injury (uniform patterns, spray or fertilizer burn, drought).
- Rotate mode-of-action groups - IRAC for insecticides, HRAC/WSSA for herbicides - and add nonchemical tactics.
Worked example
A soybean field carries a grass-like weed with a triangular stem and three-ranked leaves. The plan is clethodim, a grass herbicide. Answer: the weed is yellow nutsedge, and clethodim (a grass-only Group 1 product) will not control it. Switch to a nutsedge-active product labeled for soybean at that growth stage - for example halosulfuron - and confirm crop stage and rotation restrictions on that label.
Traps
Diagnosing from damage alone without finding the pest; spraying below threshold; calling two products from the same mode-of-action group a resistance rotation; treating drought-stressed or dust-covered weeds with contact herbicides.