M A R C H 2 0 1 9 26 POTATO GROWER North Dakota Certified Seed Potatoes 2018 Crop Winter Grow Out Results By Kent Sather, North Dakota State Seed Department, Potato Program Director Plant growth and plot maintenance was excellent for the annual 2018 Crop Winter Test grow out of North Dakota Certified Seed potato samples. 378 certi- fied seed lots were sampled by seed growers at harvest time. They were processed by our North Dakota State Seed Department (NDSSD) staff, shipped to Alger Farms, Inc. at Homestead, Florida and planted November 13-19, 2018. NDSSD staff returned to the plots for visual readings January 1-16, 2019. Results of readings are crucial to the grower, and the indus- try, since they determine seed lots eligi- ble for re-certification in 2019. These samples provide an estimate of virus incidence that may be present in the next generation (2019 Crop) of seed potatoes. Primary viruses recorded are Potato Virus Y (PVY or Mosaic) and Potato Leaf Roll Virus (PLRV). Eligibility to re-certify seed lots depends on toler- ance limitations stated in North Dakota rules and regulations for certification of seed potatoes. No more than 0.5% virus is allowed in a seed lot that will be planted for re-certification. North Dakota certified seed growers submitted 378 seed lots, representing 8,045 acres of the 13,681 acres passing the 2018 summer inspections. Based on North Dakota’s winter test disease toler- ances, sample lots representing 5,545 acres were deemed eligible for recertifi- cation in 2019 (Chart 1). The only fac- tor causing ineligibility of the remain- ing 2,500 acres was PVY incidence greater than the 0.5% virus tolerance. Table 1 shows a comparison of eligible acres by percent and represented acres with zero (0) PVY recorded at the winter test. The eligible acres for the 2019 crop are very similar to the previous year, with eligible acres being down, but insignificantly so. However, the samples with ‘0’ PVY recorded dropped by 25% compared to the previous crop. Significantly more PVY spread occurred in 2018 than in 2017. Major source inoculum of PVY resides in commercial fields and is easily vectored by aphids to adjacent or nearby certified seed fields. Dr. Ian MacRae suggested that early maturing grain crops in 2018 stimulated early movement of nonspecific aphids in the valley region. While these species of aphids are not efficient vectors of PVY, they still can spread the virus at some level. Certified seed growers will need to be discerning in replanting seed lots. Less acreage is available for recertification, and of those acres, there may be slightly more PVY incidence already in the seed. An electronic version of the North Dakota Approved Seed List for Recertification based on the 2018 Crop winter test inspections can be found at www.ndseed.com under the Potato Directory tab. Crop Year Total Acres Represented Eligible Acres % Eligible Acres Acres 0 PVY %0 PVY 2015 8,820 7,209 81 5,742 65 2016 8,338 6,797 82 4,881 58 2017 8,000 5,711 71 3,721 47 2018 8,045 5,545 69 2,834 35