Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu
Soybeans
Bacterial blight has been diagnosed from several fields in the state as well as several of our soybean rust sentinel plots. This is another disease that we rarely see except when we have wetter and cooler temperatures than normal. At first the lesions or spots can look like Septoria brown spot but these are more angular with a yellow halo around the irregularly shaped necrotic spot. Young infected leaves are often distorted (see picture below). In most situations in Delaware, yield losses would not be expected from the levels of infection that I have seen. The bacteria survive on plant residue and seeds. Plowing to bury the plant residue would be suggested.
Bacterial blight on young soybean leaves.
Soybean Rust Update
On September 9, soybean rust was reported in Effingham, Jeff Davies, and Randolph counties, Georgia; Clay, Shelby, Tuscaloosa and St. Clair counties, Alabama; and in Evangeline, Ouachita, Rapides, Richland, and St. Landry parishes in Louisiana. On September 8, soybean rust was reported in five Mississippi counties (Choctaw, Clay, Monroe, Oktibbeha, and Webster). On September 6, soybean rust was reported in Wilkinson, Jefferson, Adams and Claiborne counties, Mississippi; and Pickens county, Alabama. On September 5, rust was observed in several fields in Shelby county in the southwest corner of Tennessee.
Soybean rust has been increasing in the Mississippi River Valley and has reached TN. It is also assumed that it is present in the whole coastal plane of GA at the present time. There is still little risk at the present time of rust appearing on Delmarva for some time. Most full season soybeans in the state are at R5 or later maturity and once they reach R6 they are no longer at risk from soybean rust. Double crop beans will be more at risk if the weather should bring rust spores north in the next few weeks. There is no need to spray fungicides on soybeans for soybean rust.
