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WWW.POTATOGROWER.COM 31 ® FAST AND EFFECTIVE ORGANIC WEED CONTROL ■ Excellent tool in IPM programs ■ Helps break chemical resistance ■ No MRLs or pre-harvest interval ■ Low-foaming and easy-to-use Westbridge is growing into SAN Agrow. Contact us to learn more: (800) 876-2767 • www.san-agrow.com SUPPRESS ® Herbicide EC is the market leader and the number one herbicide approved for use on all certified organic food crops. With years of proven efficacy, SUPPRESS ® provides fast and effective broad- spectrum burndown on a wide variety of post-emergent weeds. Now approved for desiccation in potatoes! 4099-5 WestbridgeAg13s.indd 1 4099-5 WestbridgeAg13s.indd 1 2/25/22 11:09 AM 2/25/22 11:09 AM period, the prevalence of the ordinary, PVY O strain in seed potatoes dropped eight- to tenfold, concomitantly with the rise of recombinant strains PVY N-Wi and PVY NTNa , which together accounted for 98% of all PVY positives by 2021. The two most prevalent PVY strains, N-Wi and NTN, tend to be asymptomatic in the leaves or express mild, transient leaf symptoms in the currently most widely grown potato cultivars. Why is it important to know the dominant PVY strains in your area and seed lot? In order to assess the risk of PVY on yield and quality, you will need to know the variety response to PVY infection and to a particular PVY strain. To add another layer of complexity, there are isolates within each strain that may impact how the variety reacts to the infection. Recent research has identified the risk factor for commonly grown varieties and the effect of PVY strain on quality, especially for the risk of internal or external tuber symptoms. This research was done on over 60 varieties. Notable findings: • Russet Norkotah did not show necrotic tuber symptoms when infected with five different PVY strains. • Russet Burbank may show tuber symptoms if infected with NTN and N:O, depending on the isolate, but not from the other PVY strains. • Ranger Russet may show tuber symptoms when infected with O and NTN, and N:O and N-Wi, depending on the isolate tested. These results indicate that there is a variety-to-virus strain interaction, and that even isolates within a strain can react differently. Changes in PVY strain prevalence create the need for adjustments in diagnostic services, potato certification, and breeding programs developing PVY resistance. Breeding for resistance is a major goal of the SCRI-funded project, and shifts in PVY strain popularity complicate the breeding goal. The best resistance to PVY comes from an Ry gene, which provides broad-scale resistance across multiple PVY strains. Russet varieties with the Ry gene are Payette Russet and Castle Russet. Seeing how relatively quickly the Pacific Northwest shifted from having the PVY O strain be the most dominant, to the recombinant strains PVY N-Wi and PVY NTNa , emphasizes the need for continual monitoring of PVY strains dominant in the industry and to evaluate the risk of variety-specific yield and quality issues based on PVY strain infection. Results from this long-term project have been published in the journal Plant Disease and the American Journal of Potato Research. Nora Olsen (norao@uidaho.edu) is an extension potato specialist with the University of Idaho. Alex Karasev (akarasev@uidaho.edu) is a UI plant virologist. Jonathan Whitworth (jonathan.whitworth@usda.gov) is a potato pathologist with USDA's Agricultural Research Service based in Aberdeen, Idaho. PG Effects of PVY on infected tuber