Effect of rainfall in the control of onion thrips, Thrips tabaci lindeman (Thysanoptera :Thripidae) in Sokoto, Nigeria

Abstract

Field experiments were conducted in the dry seasons of 2001/2002 and 2002/2003 to study the major insect pests of onion using five dates of transplanting and five insecticidal spray regimes of λ-cyhalothrin in a randomised complete block design, replicated three times. Results indicate that thrips were the major insect pests of onion, which started colonizing onion plant in December, but the number was low until the third week of January and peaked in mid-March with up to 600 thrips/plant. In the course of the research, rainfall was recorded on 12 April, 2002 and 6 April, 2003 and this was observed to exert greater control of thrips than either planting date or the chemical (78%). In 2001/2002 season, there was a reduction in thrips population from 86-9 thrips/plant (89%) in zero spray in March transplant from 5-6 weeks after transplanting (WAT) before rising to 25 at 8 WAT, in February transplant the reduction was from 78-13 thrips/plant in zero spray. In 2002/2003 season only a slight increase in number of thrips/plant (12-15) was observed from 4-5 WAT in March transplant, but in February transplant not affected by rain there was increase was from 21-89. Where rainfall can be simulated, a greater control can be achieved, where thrips are washed away by the force of the rain, unlike chemical that may not reach the innermost leaves.