PestsPractitioner · 3 min readDraft — pending field review

Integrated Pest Management for onions, without the spray treadmill

Scout, prevent, and intervene in steps — so you spray only when you must, and the spraying keeps working.

Updated 9 June 2026

Many onion farmers spray on a fixed calendar: every week, or every few days, whether or not there is a pest to kill. It feels like protection. It is, in truth, an expense that often does the opposite of what you intend.

Why the spray calendar feeds the debt cycle

When you spray on a schedule regardless of what is in the field, two things happen. First, you buy and apply chemical you did not need on the days there was little pressure, and that cost goes straight onto the input bill and the loan. Second, and worse, spraying the same chemical again and again teaches the pest to survive it. The few individuals that withstand the spray are the ones that breed, and over seasons the population stops responding to that chemical at all. Then you spray more often, or buy a stronger product, and the bill climbs again. The calendar feels safe but it builds both resistance and debt. Integrated Pest Management replaces the calendar with attention.

The IPM ladder

Climb these in order. You only move up a rung when the rung below is not holding the pest.

Scout your field weekly. Walk the beds and look closely at the plants, not from the path but up close, in several spots across the field. You are deciding what to do based on what is actually there, not on the calendar.

Use cultural controls and field sanitation. Rotate onions with unrelated crops so pests do not build up in one spot, remove and destroy badly infested plants and crop debris where pests shelter, manage your spacing and irrigation so the crop is vigorous, and keep weeds down because they harbour pests.

Use biological and physical options. Protect the natural enemies already in your field by not blanket-spraying them away, and use physical measures such as removing affected leaves or trapping where practical. A field that still has its predators does much of your pest control for free.

Spray only when pressure crosses a threshold, and target it. When scouting shows pest numbers rising to where they will truly cost you yield, spray then, treat the affected patches rather than the whole field where you can, and stop when the pressure drops.

Knowing onion pressure: thrips

Thrips are the pest to watch most closely on onions. They are tiny, slender insects, hard to see, that hide down in the leaf folds and at the base of the plant. They rasp and suck at the leaves, and the sign you will notice first is silvery or whitish streaking and flecking on the leaves, sometimes with tiny dark specks. Heavy feeding twists and dries the leaves and checks bulb growth, so the damage shows up in your harvest. They build up fastest in hot, dry stretches. This is exactly why weekly scouting matters: thrips are easy to miss until they are many, so you look for the early silvering and act on the trend, not on a date.

Field tip

When scouting truly tells you to spray, rotate the chemical family you use rather than reaching for the same product every time. Alternating between products that work in different ways keeps the pest from adapting to any one of them, so the sprays you pay for keep working season after season. Reusing one active until it fails is how farmers end up on the treadmill.

Scout your field weekly and act on the pest pressure you actually see, climbing the ladder from prevention to a targeted spray only at threshold.

Avoid

Spray on a fixed calendar regardless of pest levels, which wastes input money and breeds resistance until the chemical no longer works.

The farmer who scouts spends less on chemical, keeps the sprays effective, and protects the natural helpers in the field. Less chemical bought is less borrowed. That is the dual benefit: a healthier field and a lighter loan.

This guide is a working draft pending field review.