If the risk of soybean rust development is high and the crop is not yet at the R6 growth stage, fungicides may be needed. For fungicides to be most effective, they must be applied close to the time the fungus initially infects plants in a field. In most cases, this means that fungicide decisions are made at a time when the risk is high, but before rust is detectable in the field. Detecting low levels of soybean rust (<10% of leaves infected) typically requires incubating leaves and observing them under a microscope in laboratory conditions by a trained diagnostician.