The Critical Onion Growth Stages For Selective Protection From Thrips Tabaci Lindeman (Thysanoptera:Thripidae) Infestation

Abstract

Field trials were conducted during 2000-2001 at KARIandrsquo;s Mwea-Tebere and Kiboko farms to establish the effect of onion thrips, Thrips tabaci Lindeman on onion bulb yields and to identify the critical onion growth stage for selective protection from the pest infestation. Yield reductions of 59 and 27% were recorded in the first and second crops respectively at Mwea-Tebere, but no significant yield reductions were observed in a third crop grown at Kiboko with low thrips infestation. A significant onion yield response to thrips infestation was observed during the 2nd month after transplanting (bulb-formation) and 3rd month after transplanting (bulb-enlargement), but no significant response was observed during the 1st month (pre-bulbing) and 4th month (maturation stage). Onion protection during bulb-formation and enlargement stages only, resulted in higher marginal returns than full season pesticide application. The studies suggest that control recommendations for onion could be refined to optimize need-based protection.