Fall 2019 Soybean Disease Update
Soybean disease pressure is picking up around the state. Alabama Extension plant pathologist Ed Sikora has observed several diseases in soybean fields in the state.
Web blight was observed in scattered fields in north and central Alabama this week. High temperatures and high humidity
favor the development of a web of fungal mycelium which can cover plant parts. The leaves typically stick together, wilt and tatter. The disease usually occurs in localized spots in the field. Some fungicides are registered for web blight control. Triazole fungicides are not effective against this disease.
Septoria Brown Spot
Septoria brown spot was observed in a field in Elmore County during the third week of August. The foliar disease is not a yield reducer, but can be confused with soybean rust. Expect to see the chocolate brown spots with a yellow halo on the older leaves.
Soybean rust has been found in nine counties in the state. The most recent report was on soybeans in Elmore County, the first report on soybean this year. Before the third week of August, the disease had been found mainly in southwest Alabama on kudzu at low levels.
Soybean web blight.
Septoria brown spot.
Sikora believes the recent high temperatures will inhibit rapid development and spread of the disease at this time. However, growers should be prepared to protect double-cropped soybeans, especially if temperatures moderate and frequent pop-up thunderstorms continue to roll across Alabama.