Virginia soybeans: Factors to consider in rust management
The Plant Pathology program at the Tidewater AREC is currently working on a weather-based advisory for soybean rust, and we are tracking when conditions are conducive to disease development. Favorable conditions include daily average temperatures between 65 and 78 ̊ F and moisture provided by periods of relative humidity greater than 95% for 10 or more hours per day. The last day in September favorable for disease development was September 9 and the current cool, dry conditions minimize the risk of SBR infection.
By the time SBR is widespread and weather conditions are conducive to the disease, most of the soybean crop in the state may be beyond R6 and no longer at risk. However, soybean rust did show up several weeks earlier this year than in 2012, and some soybean was planted later than usual. Of course no one can predict the future and there is always a certain degree of risk in all aspects of crop production. Hopefully this information and the updates to follow will help growers with decisions regarding management of soybean rust.
Fungicides for Management of Soybean Rust
Triazole or pre-mix fungicides are recommended for control of Asian soybean rust (SBR). Triazoles have some curative properties whereas fungicides with a strobilurin mode-of-action are protective in their activity and have little effect on established infections. Fungicide applications should be made prior to disease onset and when conditions are conducive for disease. Timing of fungicide sprays should be based on regional advisories or at the first sign of rust in the immediate are. Fungicides should be applied when soybeans are between R3 and R6 stages of development. If disease pressure is high, multiple applications may be necessary. Always consult pesticide labels prior to use