Potato Grower

December 2017

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WWW.POTATOGROWER.COM 45 Sure-K® is a clean, chloride- and hydroxide-free potassium solution. It can be applied in combination with other crop production or protection products and presents a very low risk of crop injury. Sure-K® can be used in any cropping situation where potassium is needed. 167626AgrLiq12h.indd 1 10/30/17 1:26 PM late-season precipitation or irrigation. Potato psyllids can be found year-round on both bittersweet nightshade and matrimony vine. This includes during the winter when psyllid populations are low on both species, and during the growing season when populations can build to high levels. But psyllid population dynamics during the warm months differ on these two plant species. Psyllid populations on bittersweet nightshade seem to increase throughout the warm months and then gradually decrease in autumn. On matrimony vine, psyllids can build to high densities during spring and autumn, but are mostly absent during the summer when matrimony vine enters summer dormancy. The disappearance of psyllids from matrimony vine seems to occur at the same time psyllids begin arriving in potato fields, leading researchers to suspect that summer defoliation of matrimony vine prompts potato psyllids to migrate to potato and other suitable hosts. ONGOING RESEARCH Research plots were setup during the summer of 2017 to specifically assess whether summer defoliation of matrimony vine prompts migration of potato psyllids. These studies are part of a larger, multi- institutional effort involving USDA-ARS, Washington State University, University of Idaho and Oregon State University scientists to improve understanding of landscape- wide interactions between potato psyllids and their crop and non-crop host plants Funding is provided through the USDA- NIFA Specialty Crop Research Initiative, the Washington State Department of Agriculture Specialty Crop Block Grant, the Northwest Potato Research Consortium, and the Washington State Commission for Pesticide Registration. While researchers did indeed see summer decline and leaf drop in water-stressed stands of matrimony vine, psyllid numbers were unfortunately too low in those stands to realistically measure dispersal rates (a region-wide phenomenon in 2017 for unknown reasons). Researchers will again be monitoring matrimony vine in 2018, with aims to confirm the hypothesis that summer dormancy by matrimony vine prompts psyllid dispersal into potato. If this psyllid response is indeed demonstrated, the timing of leaf yellowing and defoliation of matrimony vine could be used by pest control advisors, extension personnel or scientists to predict when psyllids will begin to arrive in potato fields. Finally, the numbers of psyllids occurring on matrimony vine in the spring may be found to accurately predict the numbers of psyllids that will eventually migrate into potato. Indeed, psyllid numbers on matrimony vine in May and June appear to predict numbers that will show up on potato during July and August based on data collected from matrimony vine and potatoes for the growing seasons of 2014 to 2017. Ongoing research in 2018 and beyond will reveal whether matrimony vine can be used by growers as an early warning system to predict the risk of potato psyllids colonizing potato fields. Jenita Thinakaran is a postdoctoral research associate with the USDA-ARS and University of Idaho. David Horton and Rodney Cooper are ARS entomologists. Alexander Karasev is an entomologist and plant pathologist with the University of Idaho.

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