Early blight caused by Alternaria solani and brown spot caused by the small-spored Alternaria spp., Alternaria alternata, Alternaria arborescens, and Alternaria tenuissima are observed annually in midwestern potato production areas. The use of foliar fungicides remains a primary management strategy. However, Alternaria spp. have developed reduced-sensitivity and/or resistance to many single-site fungicides such as quinone outside inhibitor (QoI), succinate dehydrogenase inhibitor (SDHI), and anilinopyrimidines (AP) fungicides in recent years. Boscalid, fluopyram, solatenol, and adepidyn are EPA-registered SDHI fungicides applied commercially to a variety of crops including potato. High intrinsic activity was observed in fluopyram, solatenol and adepidyn to A. solani isolates. Adepidyn and solatenol reduced disease severity caused by A. solani in field evaluations. Molecular characterization of 2018 A. solani field isolates determined that the frequency of the D123E and H134R SDH mutations increased. In contrast, the H278R/Y and H133R SDH mutations were found at low frequency. Adepidyn demonstrated the highest intrinsic activity against the small-spored Alternaria spp. but high intrinsic activity was also observed with boscalid, fluopyram, and solatenol. In vivo experiments demonstrated that adepidyn, solatenol, and fluopyram were more effective at managing A. arborescens and A. tenuissima than boscalid. Under greenhouse conditions, adepidyn and solatenol reduced brown spot severity caused by A. alternata to a greater extent than did fluopyram and boscalid. Results of these studies determined that accurate pathogen identification of small-spored Alternaria spp. may be important for brown spot management. Fludioxonil and cyprodinil exhibited a higher efficacy against of A. solani isolates when compared to pyrimethanil in greenhouse assays. Fludioxonil and cyprodinil were also highly efficacious against the Alternaria spp. evaluated and appear to be a good addition into fungicide rotation programs for early blight and brown spot management. Anilinopyrimidine (AP) (pyrimethanil and cyprodinil) and phenylpyrrole (PP) (fludioxonil) fungicides have demonstrated high intrinsic activity against other pathogens. Determining the efficacy of these fungicides on Alternaria spp. is important to the potato industry.

Frogeye leaf spot (FLS), caused by Cercospora sojina Hara, is a foliar disease of soybean (Glycine max (L.) Merr.). FLS has re-emerged as an important disease due to the widespread QoI-resistant fungal population in Mississippi. Growers have transitioned from a stand-alone QoI fungicide to a multi-mode of action fungicide. One disadvantage of certain MOA’s is phytotoxicity. Phytotoxicity is a concern among soybean growers as to whether or not yield is lost. Disease, phytotoxicity, green stem, yield, plant morphology, and grain quality were analyzed to determine the impacts of fungicide phytotoxicity. Yield was significantly and negatively correlated as a result of phytotoxicity. Numerical differences in phytotoxicity severity were observed among all cultivars. Phytotoxicity severity were greatest in the Hornbeck 4950 LL with an average of 26.9%. Tank-mixing dodine with Manniplex B Moly, Megafol, and Veritas decreased phytotoxicity by 8.5, 2.7, 11.4% compared to dodine as a stand-alone treatment, respectively.