Potato production systems have long been plagued by recurrent and persistent soil-borne diseases, including Fusarium dry rot (Fusarium spp.) and potato common scab (Streptomyces spp.). Eleven Fusarium spp. were isolated from symptomatic commercially grown potato tubers in Michigan. All species were pathogenic when inoculated onto potato tubers with isolates of F. sambucinum, F. avenaceum, and F. acuminatum consistently being the most aggressive. In vitro tests showed that some isolates of Fusarium spp. were insensitive to azoxystrobin, fludioxonil, difenoconazole, and thiabendazole. Insensitivity of F. incarnatum/equiseti, F. oxysporum, and F. solani to difenoconazole is a first report in North America. A field trial was conducted to evaluate the effects of fungicide and biofungicide seed treatments applied to potato seed pieces, in-furrow, or in combination for control of soil-borne F. sambucinum. The application of mancozeb to potato seed pieces was most effective and improved final plant stand, rate of emergence (RAUEPC), and total potato yields in comparison to many of the other treatments. Field trials were conducted to investigate the influence of cultivar, sulfur, cultural practices, and crop protection strategies on potato common scab control. Overall, no management strategies were completely effective in controlling common scab. Some field treatments reduced the severity of common scab; however no treatment reduced the severity to an acceptable level required by commercial potato growers or processors.
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