By Edward Sikora
Soybean rust has been detected in 43 of the state’s 67 counties. The rust pathogen, Phakospora pachyrhiza, has been found in commercial fields as far north as Limestone, Madison and DeKalb counties as of September 19. There was significant disease development in many of these fields, but a September dry spell likely kept the disease from causing a loss in yield. Fields that were sprayed with a fungicide appeared rust-free.
Many of the commercial fields were drying down rapidly. Soybeans at the R5 growth stage (pod fill) or later are not at risk from rust. However, the few fields that are still in early- to mid-reproductive growth stages can potentially suffer damage from the disease. A fungicide application might be wise if yield potential is relatively high. A fungicide product with curative activity would be the best option.
Soybean rust produces lesions on infected plants that can lead to premature defoliation and reduced yields. All commercial varieties of soybeans currently available are highly susceptible to soybean rust. Management of soybean rust will depend on early detection of the disease. Monitoring soybean fields is recommended throughout the growing season. Fungicides may reduce yield losses depending on the plant developmental stage, time when soybean rust is detected, and timing of fungicide applications.