2020 Soybean OVT Foliar Disease Evaluations: Maturity Group IV

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Field evaluations of the maturity group (MG) IV entries in the MSU OVT were conducted at each of the locations where trials were planted (Brooksville (n=2), Clarksdale, Longwood, Olive Branch, Raymond, Stoneville (n=3), Tippo, and Verona). Entries were observed for their reaction to the diseases that naturally occurred at each location. Cercospora blight, Septoria brown spot, southern blight, and target spot were the most common diseases encountered at each location. However, 2020, similar to the 2018 and 2019 seasons, was not a good year for frogeye evaluations. But, with that in mind, frogeye leaf spot data from Tippo looked to be valuable so when considering the response of the entries contained in the 2020 OVT for frogeye leaf spot susceptibility, focus those efforts on Tippo (even though the remainder of the location data are included). Be mindful that the ratings as presented are likely not as complete as they would be in a year when frogeye leaf spot produces more disease across multiple locations. Plots were observed between R6 and R6.5. Field evaluations for the presence of foliar disease were conducted using a 0 to 9 scale whereby 0=no disease and 9=excessive disease symptoms. Cercospora leaf blight was evaluated based on the presence of disease on leaves (0 to 5), petioles (6), and on pods and stems (7 to 9) based on disease intensity as assessed by coloration of plant material (leaves with distinct purple coloration and petioles, pods and main stems with purple to near black coloration). Septoria brown spot and target spot were evaluated in a similar fashion based on the presence of the disease within the plant canopy so that 0 to 3 indicated the presence in the lower canopy, 4 to 5 in the middle canopy, 6 to 8 in the upper canopy, and 9 indicative of extensive defoliation throughout the entire plant canopy and the disease in the upper most canopy. Southern blight was based on the presence of the disease within the entire plot based on a 0 to 9 scale where 0=no disease, 5=approximately half of the plot exhibiting symptoms and 9=severe southern blight characterized by dead plants. In a lot of cases, signs associated with southern blight (either white fungal growth or sclerotia) were observed at the base of infected plants.

Green stem evaluations were made using a 0-100% scale and are based on the percentage of the plants contained in the entire plot presenting green stems, green leaf material, and pods that would have reached reproductive maturity (R8) while plants maintained green plant material. A separate trip to evaluate green stem was made prior to harvest at eight of the OVT locations. The remainder of the OVT locations had been harvested prior to arriving for green stem evaluations. Note that there may be large differences between locations that are likely the result of the environmental impact on green stem or also the differences that could arise as a result of stress as would be expected between an irrigated and a non-irrigated location.

Note that locations with a non-irrigated trial are marked as location (N) with an “N” in parentheses to indicate non-irrigated.

Maturity Group IV Early Xtend (n=11 locations):

Cercospora blight 2020 CLB MG IV early Xtend

Frogeye leaf spot 2020 FLS MG IV early Xtend

Green stem 2020 Green stem MG IV early Xtend

Septoria brown spot 2020 Septoria brown spot MG IV early Xtend

Southern blight 2020 Southern blight MG IV early Xtend

Target spot 2020 Target spot MG IV early Xtend

Maturity Group IV Late Xtend (n=11 locations):

Cercospora blight 2020 CLB MG IV late Xtend

Frogeye leaf spot 2020 FLS MG IV late Xtend

Green stem 2020 Green stem MG IV late Xtend