Pest Identification, Biology, and Integrated Pest Management Decision-Making
IPM questions want a decision sequence, not a product. California tests whether you can identify the pest, justify action with a threshold, and pick a tactic that fits the site - and whether you know where the PCA recommendation fits.
The IPM sequence
- Identify the pest - insect, mite, weed, nematode, pathogen, or vertebrate - and separate it from look-alikes and beneficials.
- Monitor with sweep nets, beat sheets, pheromone traps, sticky cards, weed counts, and degree-day models.
- Compare counts to a threshold or economic injury level - the density at which treatment prevents unacceptable loss.
- Select tactics: biological (natural enemies, parasitoids, microbials), cultural (sanitation, resistant varieties, planting date, rotation), mechanical/physical, and chemical last.
- Evaluate and record the outcome.
Biology drives timing
Target the vulnerable stage: most insecticides work best on young nymphs, preemergence herbicides must be down before weed emergence, scale insects are protected by wax, and fungi need specific moisture and temperature. Degree days predict emergence: with a 50°F base and a day of 80/50, the average is 65°F, giving 15 DD; at 300 DD the generation emerges, so scout before that date, not after.
Resistance management
Rotate mode-of-action groups (IRAC for insecticides, FRAC for fungicides, HRAC/WSSA for herbicides), use labeled rates, and avoid treating the same generation twice with one group. Resistance is a population-level genetic shift that sublethal rates and repeated single-MoA use accelerate.
California angles
A PCA's written recommendation identifies pest, site, commodity, product, rate, and timing, is signed and dated, and the applicator follows it. Bee protection comes from the label and county permit conditions: avoid bee-toxic products on blooming crops and weeds during foraging hours, and check the county beekeeper notification list. Suspected new invaders or listed pests go to the county agricultural commissioner first.
Worked example
Aphids average 4 per leaf against a threshold of 10, with lady beetles and syrphid larvae present. Reasoning: below threshold, so no spray. Increase monitoring frequency, watch whether the predator-to-pest ratio is holding, and reserve a selective aphicide for a threshold crossing - with a different mode-of-action group next time.
Traps that cost marks
Spraying by calendar, spraying below threshold, misidentifying a predator as a pest, and reusing one mode of action until it fails.