Potato late blight has been found in one field north of Pasco, Wash., industry researchers say.
“Late blight is so important because it spreads very rapidly,” said Tim Waters, WSU Extension regional vegetable specialist. “The symptoms progress very rapidly in the field.”
Blight on the leaves cause lesions that kill parts of the plant that are above ground. Spores can move down into the tubers and cause infection. If those potatoes go into storage, they don’t last very long, Waters said.
Incidence is light in the field, according to the Washington State University potato pest alert. Fields between Pasco and Eltopia should be treated with a fungicide every seven days.
According to the pest alert, other fields in the Columbia Basin should be treated at a 10- to 14-day schedule and treated one to seven days before any major rainfall.
Growers are advised to check 10-day weather forecasts for rain daily. Rill irrigated fields do not need fungicides for late blight at this time. Cooler, wetter weather is favorable for late blight, Waters said.
This is the first instance of late blight found this year. Late blight occurs fairly regularly in the Columbia Basin region, Waters said.
“The last several years that we’ve found it, it has been detected relatively early, and when you detect it early you can really stop the spread of it,” he said.
Many of the roughly 170,000 acres of potatoes are planted near each other, increasing the risk of infections spreading. Waters emphasized the importance of crop rotations to break up the disease cycle. Late blight can occur in volunteer potatoes that survived the previous year’s harvest and spring up in other crops.
“You have potatoes all over the place that are not necessarily having fungicides applied to them,” he said.
Cold piles – potatoes that don’t make grade – that growers don’t cover up or bury are another risk, Waters said. They should be destroyed before the growing season.
Growers and crop consultants are urged to alert WSU researchers if they know or think they might have late blight, the better to identify the strain. One particular strain is resistant to a certain class of fungicide, while other strains can be controlled by many, Waters said.
Team members include Carrie Bomberger with the WSU Plant Pest Diagnostic Clinic; WSU Extension agents Waters and Carrie Wohleb; Washington Potato Commission director of industry outreach Matthew Blua and Gary Grove, with the WSU Irrigated Agriculture and Research Extension Center in Prosser.
The industry manages the disease regionally.
A weekly forecast goes out to growers predicts the likelihood of late blight in the area and recommended fungicide spray schedules.
If conditions are favorable for late blight, the forecast calls for a shorter interval between fungicide applications. Under less favorable conditions, the model calls for no application or more days in between.
According to WSU, growers should monitor fields thoroughly and daily for late blight and continue until harvest.
Be sure to specifically check low areas that hold moisture longer, wheel tracks, and pivot centers. Check fields near where late blight occurred the last two years. Dispose of all cull or refuse tubers and manage volunteer potato plants, especially in fields where late blight occurred the last two years.
“When we do get a field that we think has late blight, we make it a priority to go out and look at that, because it’s really important to get that notice out to growers rapidly,” Waters said.