WSU Releases Potato Pest Alert

Probability of late blight relatively high is Washington

Published online: Jun 04, 2018 Articles
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Source: iFiberOne

Washington State University has released their third potato pest alert which included an insect monitoring report and a potato disease report for the 2018 growing season.

WSU Potato alerts come in part from the Washington State Potato Commission based out of the Columbia Basin.

According to the report, beet leafhoppers (BLH) are a continuingly increasing pest in the across the Columbia Basin. Beet leafhoppers are important to potato pests because they can transmit phytoplasma (BLTVA) that causes purple top disease.

“This week we found BLH at 74 percent of the fields we monitor.  The sticky cards with BLH averaged 4 BLH per card, which is still very few.  We expect these numbers to increase and peak in June, but right now there is not much cause for alarm,” the report stated.

Along with beet leafhoppers, aphids were found at “26 percent of the fields we monitored this week; some were winged aphids on the move, and some were wingless green peach aphids settling in for the long term.”

No potato psyllid have been found yet but the report says it was announced that they have found one in southern Idaho. Psyllid don’t normally show up until late May or early June.

Extension plant pathologist Dennis Johnson says that it will be a hefty season for late blight in the Columbia Basin and additional rainfall in May could make it even worse.

“Currently, the probability of late blight occurring in the Columbia Basin this growing season is above 90 percent. This is relatively high,” the report stated.

Ways to protect crops against late blight include:
  1. Restrict irrigation until the crop is fully emerged.
  2. Cultivate potatoes so that daughter tubers form as deep as possible in the ground.  This will help protect tubers from infection.
  3. Eliminate culls and tuber refuse.
  4. Eliminate volunteer potato plants, especially in fields that had late blight in them last year or the year before. Volunteers in these fields run a high risk of being infected and are a source of infection the current season.
  5. Begin monitoring fields for late blight when plants touch within rows and continue until harvest. Field monitoring and good communications among growers of when and where (general location) late blight is present is essential for late blight management.
  6. Begin fungicide applications to sprinkler irrigated potatoes at row closure and continue at 10 day intervals until July 4th.  Another schedule will be given that week. Fields should receive a fungicide before and within 7 days of any major rainfall.
  7. Monitor fields for late blight and weather forecasts for rain.

More information, including growth and development charts and information about pest control workshops can be found in the WSU press release.