Effects of Onion Pests Muted by Straw Mulch; Colorado State University Receives Epa Award to Support Research

Onion thrips, minute insects that cause millions of dollars in damages to onion crops in Colorado and the West, can be controlled, said researchers from Colorado State University. By using straw mulch to contain onion thrips populations, growers can control the insects and the iris yellow-spot virus caused by the insects.

The Colorado State research team has received a three-year, $126,400 award, one of three national awards from the Environmental Protection Agency’s Strategic Agriculture Initiative Program for a three-year, on-farm demonstration project for the management of onion thrips and the iris yellow-spot virus in Colorado.

"This has been affecting the onion industry in Colorado and the West for five years now," said Howard Schwartz, professor in the Department of Bioagricultural Sciences and Pest Management in Colorado State’s College of Agricultural Sciences. "The damage can result in estimated losses from $2.5 million to $5 million per year for Colorado growers."

Schwartz is collaborating with Whitney Cranshaw and Raj Khosla, both professors in Colorado State’s College of Agricultural Sciences.

Colorado’s onion growing areas are primarily located east of the Front Range – from Brighton to Ault along U.S. 85 and from Kersey to Wiggins following U.S. 34. These areas account for up to 60 percent of Colorado’s onion crop; with the remaining acreage located in the Arkansas Valley and Western Slope. These regions of Colorado are good for growing onions with bulbs large enough to be classified as "colossal," used in culinary dishes such as fried onion blossoms.

The presence to thrips and iris yellow-spot virus can reduce the overall size of the onion bulb, and a reduction in bulb size cuts into growers’ profits.

Schwartz, a researcher collaborating on the project, said the use of straw mulch has proven to be more effective than conventional pesticides. Relying exclusively on high-risk insecticides for managing thrips has produced less-than-favorable results while boosting thrip populations’ resistance to insecticide.

The goal of the Colorado State project is to demonstrate that straw mulch treatment and bio-pesticides can reduce populations of onion thrips and impacts of pest feeding and virus transmission, alleviating plant stress and conserving soil moisture, Schwartz said.

Benefits include fewer pesticide applications, enhancement of predator insects, reduction of thrips and virus pressure, increased yield, conservation of soil moisture and increased return to onion growers in Colorado and Utah, as well as to the entire onion-growing industry.