Soybean Disease Update – July 31, 2009

Bob Mulrooney, Extension Plant Pathologist;

Septoria brown spot and downy mildew continue to be the most common diseases seen at the present time. In areas that have had little rainfall and spider mite injury is present be on the lookout for Alternaria and Phyllosticta leafspot on stressed soybeans. Both fungi are weakly parasitic but infect drought stressed and mite infested soybeans.

alternaria leafspot on soybean

Alternaria leafspot on mite infested soybean leaf

Soybean Rust
On July 28, soybean rust was found in Assumption Parish, Louisiana, in a soybean sentinel plot. Soybean rust scouting continues in the U.S. and Mexico. In 2009, soybean rust has been found in five states and 32 counties in United States, and in two states and five municipalities in Mexico. There is no active soybean rust in Mexico at the present time.