Scouting and Action Thresholds Help Onion Growers Reduce Insecticide Use

Onions are big business in New York. The State ranks #6 in the country for production and growers sell more than $40 million worth of product annually. Ten years ago growers routinely lost 30-50% of their crop’s value to onion thrips. Since then, new insecticides have minimized loss. Unfortunately, the new products are expensive, and were being used almost weekly creating concern that thrips may build up resistance. Dr. Brian Nault has a solution.

This article was developed for the 2017 NYFVI annual report.

In 2015 Nault, who is with the Cornell Onion Thrips Program, received a NYFVI grant to demonstrate that weekly scouting and the use of an action-threshold based insecticide program, could save growers money and help prevent insecticide resistance. As a result of his project 60% more growers used action thresholds, saving an average of $42 per acre, for a total of approximately $175,000 each year.

This project is well aligned with NYFVI’s strategic priority to “improve operational practices”. It demonstrates how incremental knowledge and refinement to production practices can reduce input costs. In this case, reduction of insecticide use to prevent insecticide resistance and other harmful off-target effects is also a strong benefit of the program.

Onion thrips (Thrips tabaci) damage onions by feeding on leaves, which reduces the size of onion bulbs. Previous research has established that onion plants can sustain a certain number of thrips  before suffering economic damage. Onion growers can use this information to spray insecticides only when needed, or when their onion thrips populations reach an action threshold of one thrips per leaf.

Nault’s team of Entomologists and Cornell Cooperative Extension Vegetable Specialists recruited 16 onion growers representing five major onion growing regions in New York to participate in its pilot Integrated Pest Management (IPM) onion thrips program in 2015.

A minimum of one onion field per onion grower was scouted weekly for onion thrips. Information on whether thrips infestation was above or below an action threshold was communicated weekly to the grower. Moreover, based on the level of thrips infestation, a recommendation on whether insecticide application was warranted and type of insecticide to use was communicated to the grower.

As a result of this information, participating growers using action thresholds made 30 to 50% fewer insecticide applications. This reduction saved those growers money, reduced harmful off-target effects and will slow the onset of insecticide resistance. Additionally, 30 or more growers were educated about the benefits of scouting and action thresholds through presentations and field days.

A post project survey of growers found that the majority plan to continue to use action thresholds to manage thrips.

Christy Hoepting, CCE educator and scout in Elba Muck, and David Sorbello, onion grower from Oswego county .