Management of thrips (Thrips tabaci) in bulb onion by use of vegetable intercrops

Abstract

Field experiments were conducted between July 2008 and May 2009 to evaluate the effectiveness of intercropping carrot (Daucus carota), spider plant (Cleome gynandra) and French bean (Phaseolus vulgaris) with onion in the management of thrips (Thrips tabaci) in onion. Each of the three onion varieties, Bombay Red, Red Creole and Orient F1 were intercropped with each of the vegetables and insecticide imidacloprid was used as a standard check. Thrips damage incidence and severity were determined every 7 days with damage severity being estimated on a scale of 1-5. Total and marketable bulb yield were determined at physiological maturity. Intercropping onion with spider plant and carrot significantly (p ≤ 0.05) reduced thrips population by up to 45.2% and 21.6%, respectively but French bean had no significant effect. The three vegetable intercrops significantly (p ≤ 0.05) reduced thrips damage severity, with spider plant having the greatest reduction of up to 15.7%. Intercropping onion with carrot and spider plant significantly (p ≤ 0.05) reduced onion bulb yield while the effect of French bean and imidacloprid on yield was not significant (p ≤ 0.05). This study showed that spider plant and carrot can be utilized in the management of onion thrips. However, further investigations should be undertaken on their optimal spatial arrangement in an intercropping system to avoid reduction in bulb yield and, therefore, achieve optimum onion productivity