Potato Grower

May 2014

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42 Potato Grower | MAY 2014 Test plots at the University of Idaho Kimberly R&E Center are helping researchers better understand the relationship among hairy nightshade, green peach aphids and potato virus Y. An Interesting Relationship What do weeds, insects, and potato viruses have to do with each other? UNIVERSITY OF IDAHO by Pamela J.S. Hutchinson University of Idaho research concern- ing the interaction between hairy night- shade, green peach aphid and Potato Virus Y (PVY) is currently being conducted by potato cropping systems weed scien- tist Pamela J.S. Hutchinson as part of a larger PVY grant from the Specialty Crop Research Initiative (SCRI) and the Idaho Potato Commission. Results so far indi- cate that when relatively large (8 inches or taller) hairy nightshade is present in potatoes where green peach aphids are spreading PVY from infected potato plants, the virus spreads farther than when smaller or no hairy nightshade are present. In fact, a greater percentage of these tall hairy nightshade become infested by green peach aphids than the smaller hairy nightshades. The aphids then seemingly move from the infected potato plants onto the large hairy nightshade and subsequently to potato plants in adjacent rows faster than when smaller or no hairy nightsahde are present. Additional research shows that hairy night- shade at one-per-meter row density resulted in greater PVY spread by green peach aphids than when a three-per-meter row den- sity was present. In this case, Hutchinson thinks that the gree peach aphids may have remained longer on the more densely trans- planted hairy nightshade rather than mov- ing to adjacent potato rows. Hairy nightshade is prevalent in many U.S. potato-producing areas. Hutchinson previously discovered that when this weed is present between 7 and 24 days after potato emergence—known as the critical weed interference period before the crop becomes competitive—tuber yield and quality reductions can occur. Competition with hairy nightshade at two per meter row in russet Norkotah or one per meter row in russet Burbank season-long also can cause yield and quality reductions. Most growers have adopted early-sea- son hairy nightshade control measures to prevent these losses. The PVY vector, green peach aphid usually does not appear until after this critical interference period for hairy nightshade in potatoes is over. Other U of I researchers found that hairy night- shade can become infected with and serve as a source for PVY; green peach aphids prefer hairy nightshade over potato plants; and, to add insult to injury, are more pro- lific on this weed than on potato plants. If hairy nightshade is not controlled well early in the season, a plant could be as tall as 12 inches and/or spreading out below the potato canopy at the time of green peach aphid flight. In addition, hairy nightshade is one of those weeds that can germinate throughout the entire growing season. Hence, if control does not last long

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