Effects of staggered planting dates on the control of Thrips tabaci Lindeman and yield of onion in Nigeria

Abstract

Eight–week old onion seedlings were transplanted from December to April in 2001-2002 and November to March in 2002-2003 growing seasons to assess the level of thrips damage and its effect on onion bulb yield. Results obtained revealed that thrips started appearing from January but the number was very low until end of February when the population reached 12 thrips/plant. November transplant was free of thrips up to 9 weeks after transplanting (WAT), December transplant up to 8 WAT, January transplant up to 6 WAT, while February, March and April transplant had population of >5 thrips /plant at 4 WAT. There was a significant difference (P< 0.05) between plantings from 4-14 WAT. The peak of thrips incidence in the various transplants were as follows: November at 15 WAT (120), December at 12.5 WAT (234), January at 9.5 WAT (373), February at 8.5 WAT (217), March at 6 WAT (41.2) and April at 5 WAT (20). Onion bulb yields were also found to differ in descending order as follows: November (48 t/ha), December (42 t/ha), January (13.5 t/ha), February (5.5 t/ha) and March (1.5 t/ha). Key words: Onion, Thrips tabaci, weeks after transplanting.