Onion World: The Voice of the Onion Industry

Onion Diseases/Pests

Yellow Nutsedge
Yellow nutsedge multiplies faster than you can say “spring planting” and can completely take over an onion field in a matter of months.

Part of the problem of this weed, according to Corey Ransom, of the Oregon State University Malheur Experiment Station in Ontario, Ore., is that onion field conditions favor its growth. That’s because onions don’t form big canopies during the season, making it hard to compete with yellow nutsedge.

The weed also favors high nitrogen and soil moisture conditions, although it can survive dry environments. And once the yellow nutsedge gets started in a production area, it’s almost impossible to wipe out; a very hearty weed indeed.

“Yellow nutsedge is definitely becoming or is the worst problem that we face in the Ontario onion production area,” he said during his presentation at the 52nd Weed Conference held in Yakima, Wash., in November hosted by the Washington State Weed Association.
-Carrie Kennington, editor, Onion World, January 2003, page 14.

Yellow nutsedge tubers vary in size depending on age and depth and are the biggest cause of weed spread.

Onion Maggot
Speaking during this year’s New York Vegetable conference Feb. 11-13 in Syracuse, Ed Grafius, a Michigan State University researchers, said some insecticides have been effective for controlling onion maggot, but in recent years the pest has been building up resistance.

To get around that and control the problem long-term, Grafius suggested coupling insecticides with biological and cultural methods may be the answer.

Planting a little later than normal may also benefit fields with maggot problems, Grafius explained.

“You can make a huge difference in onion maggot damage just by that one practice,” he said.

Row covers in May or June to prevent maggot egg laying may be a good option, he also added.

In his research report, Grafius said that post-harvest practices can also make a big difference in maggot control. Harvesting as cleanly as possible and tilling the remaining culls below sprouting depth can reduce the food available for onion maggot.

Growers also should consider planting a rye cover crop soon after harvest because it can make it harder for maggots to find onion culls, the researcher said.
-Carrie Kennington, editor, Onion World, March/April 2003, page 16.

Onion Thrips
Reports indicate that thrips can significantly reduce onion yield and bulb size when they are not controlled. The severity of thrips infestations is usually highest in hot, dry years because more generations are produced in the hot weather and populations do not suffer high rates of mortality due to the lack of rainfall. The major control strategy for onion thrips is the frequent use of insecticides and growers may apply treatments weekly, especially in hot, dry years. There is concern that such intensive treatments may result in the development of resistance.
-A.M. Shelton, et. all, Cornell University, Onion World, May/June 2003, page 20.

Online Pest Network
Onion fiends may have met their worst nightmare: The Treasure Valley Pest Alert Network. The Web site, www.tvpestalert.net, offers the latest updates on insect, weed and disease outbreaks in Eastern Oregon/Western Idaho crops.

The concept was developed through a collaborative effort on the part of Treasure Valley extension agents and researchers of the University of Idaho and Oregon State University. Their goal was to discover outbreaks sooner in order to alert growers and recommend a course of action, all to keep the pest from spreading. With the launching of the site in March 2001, they may have fulfilled that dream.

We've been surprised about how much use it's gotten," says Lynn Jensen, of the Malheur County OSU Extension Office.

In the 2001 season, 114 subscribed to receive email pest alerts and the site was visited 5,899 times. In 2002 email subscriptions were up to 213 and the site was hit 8,975 times.
-Carrie Kennington, editor, Onion World, May/June 2003, page 8.

Iris Yellow Spot Virus
Dr. Howard Schwartz, Colorado State University, reported that the onion industry continues to be concerned over Iris Yellow Spot Virus, a disease now identified in northern Colorado as well as the Treasure Valley region of Idaho and Oregon. At least two infected fields were identified in northern Colorado last year, with infection rates ranging all the way from 20 to 100 percent.

There are no known quick fixes for the disease, Schwartz said, noting that he personally feels there may be an interaction between the number of thrips present in a field, heat and moisture stress. All, he said, appear to compound the problem. Anything that can be done to reduce the effects of all three should be helpful.
-Brent Clement, managing editor, Onion World, March/April 2003, page 5.