CORVALLIS, Ore. – Researchers at Oregon State University are teaming with colleagues in Washington and Idaho to help farmers combat an insect-transmitted disease that could devastate the Pacific Northwest’s $9 billion potato crop.
Silvia Rondon, an OSU Extension entomologist, and Oregon State colleagues Stuart Reitz and Molly Engle, are collaborating with Northwest university and industry partners on a five-year, $2.7 million study of zebra chip disease, which discolors the flesh of potatoes and makes them unmarketable.
The disease is caused by a bacterium carried by a tiny flying insect called the potato psyllid. It has caused serious problems in the southwestern United States, severely damaging the potato crop and causing millions of dollars in losses, according to Washington State University entomologist Bill Snyder, the study’s co-leader.
For the new study, Rondon’s team will step up ongoing trapping and monitoring of potato psyllids and coordinate these efforts in all three states. Others on the study will probe the DNA of the psyllids and the bacteria they carry.
The researchers will map in detail where each genetic variety of psyllid is coming from, which strain of the zebra chip bacterium the insects are carrying, how they are moving across the landscape, and how their activity is affected by weather, topography and presence of alternate host plants.
From this information they will develop predictive models and integrated pest management (IPM) guidelines, delivered through a mobile-friendly website that will enable farmers to evaluate their disease risk and spray only when and where they need to.
Zebra chip disease was unknown in the Northwest until 2011, when a surprise outbreak sent tremors through growers of the Northwest’s most valuable vegetable crop.
“It was in only a handful of fields in 2011,” said Rondon, a College of Agricultural Sciences researcher based at OSU’s Hermiston Agricultural Research and Experiment Station, “but it was severe enough to cause significant economic damage.”
The following year the disease spread widely through the potato-growing areas of northeastern Oregon and southeastern Washington.
Psyllid adults and immature nymphs land on potato leaves and feed on them, transmitting the bacterium into the leaves through their mouthparts. The infection makes its way down into the developing tuber and interferes with its processing of sugars. An early-season infestation can kill the plant; a mid- to late-season one can ruin the crop.
Potatoes affected by zebra chip disease are safe to eat, Rondon said, but they’re unappetizing – the flesh is mottled with brown streaks that caramelize and turn bitter-tasting when the potatoes are fried – so they can’t be used for chips or French fries, two of the highest-value potato products.
To protect their crop, growers typically spray insecticides weekly from June through harvest, even if they don’t know whether the psyllids are present or are carrying the disease.
“These sprays are not only expensive, but they run the risk of inducing pesticide resistance,” said Rondon. “But right now they feel they have no choice. We want to develop effective integrated pest management programs, and to do that, we have to be able to predict how the disease spreads.”
After the 2011 outbreak, Rondon, Reitz, and others began intensively monitoring potato psyllids across the inland Northwest, trapping the bugs in and around potato fields and tracking where they were coming from and how they moved.
Researchers have so far identified five genetically distinct types of potato psyllids, Rondon said. One, the northwestern type, lives year-round in the region. It overwinters in bittersweet nightshade, a weed that grows around potato fields planted near canals and ditches. The insect may also take refuge in other wild plants such as bindweed, or in piles of culled potatoes.
Another psyllid type, the western type, probably comes in from California in late winter, Rondon said. All psyllid biotypes can carry the zebra chip bacterium. All appear to travel over long distances, possibly carried by the wind or hitching a ride on transported plants.
The study is funded by the U.S. Department of Agriculture. Collaborators besides OSU are Washington State University, University of Idaho and the Potato Research Consortium, which is composed of industry representatives from each Northwest state.