Efficacy of Neem-Based Formulations Against Whitefly in Cotton Under Field Conditions

Abstract

Neem-based products are among the most widely recommended botanical options against the whitefly Bemisia tabaci in cotton, a pest that damages the crop by feeding, by fouling lint with honeydew and by carrying viruses, and that has repeatedly outrun synthetic insecticides. This mini review asks how far the case for neem rests on field evidence, as opposed to laboratory bioassays. It draws on published work on azadirachtin and related compounds, on whitefly biology and resistance, on natural enemies and on the design of efficacy trials, and it reports no new data. Neem acts mainly by deterring feeding and egg laying and by disrupting development of immature stages, so it is slow and works best against nymphs. Field performance is variable. The active content of crude products differs between batches, azadirachtin breaks down quickly in sunlight, undersides of leaves in a dense canopy are hard to wet, and immigration from neighbouring crops can mask a real effect. Laboratory results therefore tend to overstate what a farmer will see. Neem is gentler on many natural enemies than broad-spectrum chemistry but is not free of non-target effects. The review concludes that neem is best treated as a component of integrated management, and it lists what a trial must report before a field claim can be trusted.