Controlling potato psyllids key to managing zebra chip

Potato psyllids were found in 88 percent of the fields we monitored this week. This means psyllids are continuing to migrate into fields throughout the Columbia Basin. The numbers of psyllids are higher in the Lower Columbia Basin, but they are being seen throughout the region. We are collecting a lot more potato psyllids on sticky cards this season than we did in July of previous seasons. The likelihood of zebra chip occurring in potato fields in the Columbia Basin increases with these large numbers of psyllids. All potato growers should be focusing on potato psyllid management now, because we can’t predict where and when zebra chip will show up.

Potato psyllids can spread a bacterium (Candidatus Liberibacter solanacearum), that causes zebra chip disease. The first reports of zebra chip in the Columbia Basin are usually in July. Symptoms of zebra chip can include tightly rolled leaves, chlorosis (yellowing) of leaves, purple discoloration of leaves, aerial tubers, axillary bud proliferation that makes the plant look bushier, leaf necrosis leading to early plant death, and a characteristic brown discoloration of the internal tuber tissues. There are a few diseases (especially purple top disease) and physiological disorders (heat stress and others) that exhibit similar symptoms. If you see symptomatic plants across the entire field, then it is probably not zebra chip or purple top. Diseases usually manifest in zones or areas in the field, which expand as the disease spreads. If you suspect the plants may have zebra chip, then cut some tubers and look for internal discoloration. If you see any kind of brown discoloration, then you should have the plants tested for zebra chip. Please contact Carrie Wohleb at cwohleb@wsu.edu or Tim Waters attwaters@wsu.edu to report, confirm, or diagnose zebra chip.

These images, taken at the end of July in 2015, show typical symptoms of zebra chip disease. Photos: WSU Extension

Zebra chip can be managed by controlling potato psyllids. It is not possible to stop psyllids from entering the fields, but it is possible to keep their populations in check and minimize spread of the disease. The insecticide efficacy table BELOW includes information about products that are registered to control psyllids. These insecticides usually target specific life stages (adult, nymph, egg). In fields with nymphs and eggs, it would be wise to apply a product that will control these life stages. Click HERE for more information about managing potato psyllids

— Carrie Wohleb, Washington State University

Source: Washington State University Extension Potato Pest Alert