J U L Y / A U G U S T 2 0 1 9 28 POTATO GROWER Russet, had relatively lower visual wilt symptoms throughout the growing season with and without VAPAM® use (Fig 1). During late August, wilt symptoms in the non- fumigated block reached 50% and more for Dakota Jewel, Chieftain, WND8625-2Russ, and others. Overall, wilt symptoms were less for the VAPAM® treatment compared to the non-fumigated treatment. Quantification of the pathogen DNA with RT-PCR revealed that V. dahliae colonization in potato plant above ground stems was influenced by both VAPAM® treatment and genotype. Pathogen colonization in potato genotypes was significantly lower in the block with VAPAM®, compared to the non-fumigated treatment. Among advancing selec- tions, AND97279-5Russ, ATND99 331-2PintoY, ND12248Y-2R, ND 1382-2R, and WND8625-2Russ had low levels of colonization when grown in both the fumigated and non-fumigated soils, indicating potential resistance to V. dahliae (Fig 2). In contrast to previous stud- ies (Pasche et al. 2013, Novy et al. 2003) we found very low VW symp- tom and colonization for Russet Norkotah and moderately high VW and colonization for Bannock Russet. The early vine maturity and senescence of Russet Norkotah may have allowed for avoidance or limit- ed colonization by the pathogen. In reviewing the stem colonization data for Bannock Russet, only one sample had very high colonization, thus increasing the average value of colonization. The standard devia- tion for stem colonization was very high, perhaps skewing results. Vine maturity was significantly influ- enced by VAPAM® treatment. Across all genotypes, vine maturity was significantly later with VAPAM® treatment, as expected, compared to maturity in the non- fumigated treatment (Fig 3). VAPAM® treatment and genotype separately influenced total tuber yield. Average total tuber yield across genotypes was significantly lower with VAPAM® (344 cwt/acre) compared to yields without VAPAM® (379 cwt/acre). The total tuber yield ranged from 152 cwt/ acre for ND124C-1 without VAPAM® to 599 cwt/acre for Chieftain without fumigation (Fig 4). Tuber size ranges of 0-4 oz, 4-6