Washington State University Plant Pathologist Dennis Johnson said the risk of late blight increased last week because of cool, wet weather that placed the crop at high risk. Seven to 10 days of dry, warm weather have been forecast.
Risks vary within the region, depending on weather and other local factors.
Washington's potato industry has a farm-gate value of nearly half a billion dollars. The risk in the Prosser area is much lower, at about 35 percent. Johnson bases his estimates on a computer model that uses April and May rainfall. Irrigation practices are important. Johnson warns that late blight often develops where sprinklers overlap, and within the first 80 to 100 feet out from the center of pivot-center sprinkler systems.