Less is more: Evaluating reduced applications of fertilizer and insecticide for management of onion thrips (Thrips tabaci) on onion

Onion thrips (Thrips tabaci) is a major pest of onions and most commonly managed through insecticide applications. Applying an insecticide only after reaching an action-threshold can reduce the development of resistance to insecticides, save money, and limit non-target effects of insecticides without compromising effective control. In addition to reducing insecticide application frequency, the rate of fertilizer applied could aid thrips management. Nitrogen and other nutrients are crucial to onion development but high rates can lead to greater onion thrips densities. In this study, we investigated the integration of action-threshold based applications and reduced fertilizer applications for their effectiveness in onion thrips management within New York onion fields. We evaluated how using a full rate of fertilizer, half rate of fertilizer, and no fertilizer paired with either weekly insecticide applications or action-threshold based applications affected thrips densities and onion yield. We replicated this study at twenty one site-years between 2019-2021 in western and central New York, using varieties and full fertilizer rates chosen by our cooperating growers. Thrips numbers were consistently greater in the action threshold treatment than in the weekly spray treatment, averaging twice as many, but onion yield was unaffected, indicating that action thresholds were successful at maintaining thrips below acceptable levels while making 30% fewer insecticide applications. Fertilizer had no impact on either thrips numbers or yield in either year. Although managing onion thrips without reliance on insecticides remains a challenge, we have demonstrated that growers can reduce both fertilizer and insecticide usage without costs to onion yield.