Management practices for the suppression of Verticillium wilt of Russet Burbank potato include sanitation, use of optimum sprinkler-irrigation practices, soil solarization, and an adequate soil fertility program. Among all cultural factors considered, nitrogen (N) deficiency in potato tissue was most commonly associated with the severity of Verticiilium wilt in Russet Burbank potato. Field studies have shown that increased N availability suppresses Verticiilium incidence on cv Russet Burbank while having no effect on cv Norgold Russet. Studies from both greenhouse and field show that the colonization of V dahliae in potato stem tissue is suppressed in cv Russet Burbank when the availability of Phosphorous (P) is increased to the optimum. Following one season of cropping with Russet Burbank potato, the treatment providing the optimal N availability also suppressed the increases of V dahliae populations in the soil during the following year of consecutive cropping. Similarly, after two seasons of continuous potato cropping, treatments with optimal P had lower soil populations of V. dahliae in soil. Results show the suppression of Verticiilium wilt with optimal fertility. Verticiilium wilt [caused by either Verticiilium dahliae Kleb, (microsclerotial form) or Verticiilium albo- atrum Reinke and Berthold (dark mycelial form)] is one of the most severe diseases of potato in the United States. Potato yields, tuber size, and specific gravity may be substantially reduced by this disease, depending on severity, time of occurrence, and growing season. In Idaho and other arid growing regions of the United States, Verticiilium wilt is caused by Verticillium dahliae Kleb. Idaho field studies involving cropping practices, soil fumigation treatments, solarization, and Verticillium-resistant potato clones all support the importance of V dahliae upon potato yield. Data from these studies show that yield losses due to V. dahliae commonly approximate 5 to 12 metric T/ha (5, 6). Table 1 illustrates the effect of several cropping practices upon relative V dahliae populations in soil with the effects upon both disease severity and potato yield. With continuous cropping of Russet Burbank, V dahliae populations in soil increased, and yields were reduced by 18 to 19 metric Tlha when compared to locations that had been allowed to remain either weed-free and fallow or where corn had been previously cropped. It was estimated that V dahliae was influencing yield by about 10 to 12 metric Tlha based on a regression analysis of yield as a function of V dahliae populations in soil. Similarly, when V dahliae was suppressed by fumigation treatments involving mixtures of dichloropropene and picfume, yields more significantly increased by 6.5 to 12 metric T/ha (5). Although many factors may influence yields, clones with higher Verticillium resistance than Russet Burbank generally out-yield Russet Burbank. Figure 1 demonstrates the effect of solarization (a technique involving the laying of clear plastic on soil for the purpose of elevating soil temperatures to kill V dahliae). When Verticillium was controlled in this manner (lo), there was no significant yield difference between the Russet Burbank potato and the highly resistant A68113-4 clone. The A68113-4 clone grown in non-solarized soil out-yielded the Russet Burbank in non-solarized soil by 31 percent while the solarization treatment significantly increased yield for the Russet Burbank and A68113-4 clones by 46 and 18 percent, respectively. These yield responses were observed in a field where inoculum levels of V dahliae were relatively low (2.10 cfulgrn of soil). With these losses, the need to develop control procedures is great and to achieve this control the need also exists to accurately evaluate the effect of treatments upon V dahliae. Our Idaho studies have routinely utilized such a procedure (9) in combination with comparisons of both disease severity and yield. © 1990 Springer.
