Thanks to cooler temperatures, the disease pressure on vegetable growers across the Inland Northwest has been relatively light, but growers are reminded to continue to scout. Dr. Tim Waters with Washington State University said typically this time of year, potato growers need to worry about late blight, while onion growers need to keep an eye out for Downy Mildew. Waters said at this point, Late Blight has been tempered by the cooler temperatures, but that doesn’t mean growers should grow complaisant.

“Potatoes are closing canopies right now, so there’s not as much air movement as there was earlier on, and the conditions are a little more conducive for Late Blight.  We’ve got spore traps out, and I haven’t heard any, there have been no positive hits from the spore traps, and I haven’t heard anything from any consultants or growers with Late Blight.  But now is a good time to watch for that.”

For onion growers, Waters says there have been reports of Downy Mildew, specifically in a seed crop in the northern portion of the Columbia Basin. Because of that Waters says growers need to actively scout, and if they come across Downy Mildew, he recommends a fungicide application to control it.

For more on your local disease pressures, or treatment options, contact your local Extension office.

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