By Gina Greenway, Agricultural Economist and Assistant Professor, College of Idaho
With another year’s onion harvest in the books, a familiar problem remains a timely concern. Thrips and thrips-transmitted Iris yellow spot virus (IYSV), successfully deliver the threat of a one-two-punch to grower returns. Management expenses contribute to increased costs of production while any reductions in bulb sizes will hit the revenue line – a perfect combination to put the squeeze on profit.
Thrips pressure will vary from year to year, field to field, by growing region and with environmental factors. Management costs will depend on severity of pressure and choice of products used.
To try to capture the impact of thrips and IYSV, I estimated management expenses under a few common scenarios.
A grower spraying four times incorporating two applications of active ingredient spirotetramat plus one application each of active ingredients spinetoram and methomyl would have spent about $168 per acre on product costs alone this growing season. Application costs would further increase the price tag depending on method of application and whether the insecticides were delivered alone or as part of a tank mix.
A grower who sprayed six times using Aza-Direct and M-Pede, plus two applications of spirotetramat, one application of abamectin and two applications of spinetoram would have spent about $245 per acre.
A grower who sprayed eight times incorporating two applications of spirotetramat, two applications of abamectin, two applications of spinetoram and two applications of methomyl would have spent about $305 per acre.
No doubt about it, managing thrips is frustrating and expensive.
As we think about the future, it will continue to be important to follow best management practices for preserving long-term-efficacy insecticides. Judicious scouting and efforts to hone in the timing of applications will also help.
Research will broaden the toolkit for managing thrips and IYSV, as well. A team of research and extension scientists across major U.S. onion growing regions is working to further develop practical integrated pest management tactics for thrips and IYSV and to ensure the long-term sustainability of onion production by releasing germplasm that could lead to the development of thrips- and IYSV-resistant onion varieties.
