Effects of Transplanting Dates and Insecticide Frequency in the Control of Thrips tabaci Lindeman (Thysanoptera:Thripidae) on Onion (Allium cepa L.) in Sokoto, Nigeria

Abstract

Two factors, transplanting date and insecticide frequency were combined to evaluate their effects in reducing population of thrips and yield of onion. Transplanting was done at monthly interval from November through March, while spraying was done fortnightly, starting from three weeks after transplanting (WAT) to nine WAT (3, 5, 7 and 9) using knapsack sprayer at 18.67 g a.i./ha. Results showed that early transplanting done in November and December had fewer thrips than the subsequent ones. At 7 WAT, late transplanting made in February had up to 191 thrips/plant and<1 in the early transplants. First spray was effective in reducing thrips by about 76% and second and subsequent sprays were less effective. There was significant difference between treatments (P<0.05) in spray at 4, 6, 7, 9 and 10 WAT and the bulb yield of onion. The yield showed that two sprays produced up to 52.53 t/ha, nearly doubling the control plots with 31.6 t/ha. November transplant produced up to 60 t/ha and December transplant 51.82 t/ha in three-insecticide spray. The average weight of bulbs from plots with 2 sprays and control plots were 238 g and 155 g, respectively.