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Reducing Onion Thrips Populations in Onion by Optimizing Nitrogen Levels at Planting 2010

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Project Leaders: Brian Nault, Entomology, NYSAES, Cornell University

Abstract: Onion thrips continue to cause significant losses to New York's onion industry and alternative management strategies are needed. To address this issue, we sought to reduce thrips populations by minimizing nitrogen use while maintaining high bulb yields. Our results indicated season total numbers of onion thrips larvae could be reduced significantly (15 to 33%) if lower than recommended rates of nitrogen were applied at planting (50 to 60% of the standard rate of 125 lbs/acre). The total number of market-sized bulbs produced tended to increase with increasing levels of nitrogen and the greatest number of bulbs was produced in the treatment that received 150% of the standard amount of nitrogen applied at planting. However, there was a positive trend between the number of rotten bulbs at harvest and the amount of nitrogen applied at planting. We suspect that even more market-sized bulbs in the higher nitrogen treatments will rot in storage. Consequently, we may find that treatments receiving lower levels of nitrogen (e.g., 62 to 94 lbs per acre) produce a similar or greater number of marketable bulbs as those receiving the higher nitrogen levels. If so, reducing nitrogen levels at planting relative to the standard of 125 lbs/acre will not significantly reduce overall marketable bulb yield, but will reduce cost of nitrogen used and reduce excess nitrogen that might cause deleterious impacts on the environment. Moreover, lower levels of nitrogen will reduce thrips densities that will permit growers to use fewer insecticide applications, saving them money and reducing potential nontarget effects.