Effect of Different Nitrogen Regimes on Onion Thrips,<i>Thrips tabaci</i>Lindemann, on Onions,<i>Allium cepa</i>L.

Abstract

Six rates of nitrogen were evaluated on onion thrips, Thrips tabaci Lindemann, on onions, Allium cepa L., in Quetta, Balochistan, Pakistan, in 2002 and 2003. Soil in the region is sandy loam, alkaline, moderate in calcium, and very low in nitrogen, phosphorous, and potassium. Low (50 kg N/ha) and optimum (150 kg N/ha) amounts of nitrogen applied to soil had no effect on abundance of thrips, although abundance of thrips (7.6 per plant) decreased at 150 kg of nitrogen per hectare. The maximum abundance of thrips (13 per plant) was observed with high rates of nitrogen (200 and 250 kg/ha), which increased abundance of thrips as much as 73.9%. Onion yields increased with nitrogen to 200 kg/ha. A rapid decrease in yield occurred when 200–250 kg/ha of nitrogen was used. Maximum yield (15,250 kg/ha) had the best cost-benefit ratio (1.43).