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Soybean (Glycine max [L.] Merr.) production is influenced by planting date, but its impact on yield in fields infested with Macrophomina phaseolina (Tassi) Goid. is unknown. A 3-year study was conducted in M. phaseolina-infested fields to assess the effects of planting date (PD) on disease severity and yield using eight genotypes, four of which are reported to be susceptible to charcoal rot (S), and four reported with moderate resistance (MR) to charcoal rot (CR). The genotypes were planted in early April, early May, and early June under irrigated and nonirrigated conditions. There was planting date by irrigation interaction for area under the disease progress curve (AUDPC) where May PD was significantly lower compared to April and June PDs in irrigated environments but not in nonirrigated environments. Correspondingly, yield in April PD was significantly lower than that of May and June. Interestingly, yield of S genotypes increased significantly with each subsequent PD, while yield of MR genotypes remained high across all three PDs. The interaction of genotypes by PD on yield revealed that the MR genotypes DT97-4290 and DS-880 had the greatest yields in May compared to April. While May PD had a decreased AUDPC and an increased yield across genotypes, the result of this research suggests that in fields infested with M. phaseolina, early May to early June planting coupled with appropriate cultivar selection provides maximum yield potential for western Tennessee and mid-southern soybean growers.

Phomopsis seed decay (PSD) caused by Diaporthe longicolla has been documented as part of a soybean (Glycine max) fungal disease complex that affects the quality of soybean seed. Soybean-producing countries that have not yet documented the presence of PSD impose soybean seed import restrictions to protect their soybean production. The purpose of this study was to determine the frequency of occurrence of Diaporthe spp. in Paraguay. In 2006, 16 isolates of Diaporthe were recovered for the first time from soybean seed in San Alberto, Paraguay in the south-eastern section of the country. The 16 isolates were used to inoculate mature pods harvested from greenhouse grown PSD-susceptible soybean cultivar ‘Maverick’. Among the16 isolates, six isolates (TN 214, TN 218, TN 224, TN 226, TN 227 and TN 229) caused infection on both pods and seeds within pods. Two groups of isolates were identified based on conidial types: isolates that produced only α conidia and isolates that produced both α and β conidia. The...