A working pest calendar without a single pesticide

The usual complaint about organic pest control is that it does not work. Usually what did not work was a neem spray applied after a bollworm population had already established, at a concentration guessed on the spot, in the middle of a hot afternoon.

Biological control is preventive. It is a calendar, not a rescue.

Organic pest control starts with scouting

Walk five spots per acre twice a week. At each spot look at five plants, and look under the leaves — that is where eggs and early instars are. Count what you find and write it down. Without a count you cannot tell whether a population is building or collapsing, and you will spray on anxiety.

Economic threshold levels are published for most crops. For cotton bollworm it is roughly one egg or larva per plant; for brinjal shoot and fruit borer, 5% shoot damage. Below the threshold, spraying costs more than the damage.

Traps do the early work

• Pheromone traps — five per acre, changed monthly. These catch males and, more importantly, tell you the week a flight begins. That week is when your neem application matters.
• Yellow sticky traps — for whitefly, aphids and leafminer. Ten per acre at canopy height, raised as the crop grows.
• Blue sticky traps — for thrips, which ignore yellow.
• Light traps — one per two acres, run for the first three hours after dusk only. Running them all night kills beneficials.

Neem, applied properly

Azadirachtin is an antifeedant and growth regulator. It does not knock down adults, so judging it by dead insects on the ground is judging it by the wrong measure. It stops early instars from moulting, which is why timing against the trap catch matters.

Getting the application right

• Use a formulation with a stated azadirachtin content — 1500 ppm or 10000 ppm — not unlabelled oil.
• Spray in the last two hours before dusk. Azadirachtin breaks down in ultraviolet light within hours.
• Add a wetting agent; neem oil beads off waxy leaves.
• Cover the underside of the leaves. This is most of the job and most of what gets skipped.
• Repeat at seven to ten days during a flight. One application is not a programme.

Release natural enemies on the trap signal

Trichogramma parasitises moth eggs, so it must be released as a flight begins, not after larvae appear. Cards carrying about 20,000 parasitised eggs are stapled to the underside of leaves in the evening, six cards per acre, repeated weekly for three weeks.

Chrysoperla larvae handle aphids, whitefly nymphs and small caterpillars. Release at 5,000 per acre. Both are living material — order for a specific date, keep them out of the sun, and release the same evening they arrive.

The part of organic pest control that costs nothing

Border rows of maize or sorghum around cotton give predators somewhere to live. Marigold as a trap crop pulls Helicoverpa away from tomato. Deep summer ploughing exposes pupae in the soil to birds and heat and reduces the following season’s first flight measurably.

Every hour spent scouting saves more crop than an hour spent spraying.

None of this is free of failure. In a bad year, a population will get past all of it. But the farm that scouts, traps and times its applications will meet that year with predators already present, and will lose a percentage rather than a field.

Further reading: the Directorate of Plant Protection, Quarantine and Storage issues pest advisories that underpin any organic pest control calendar.