How does Asian soybean rust affect soybeans?
When ASR colonizes soybean plants, leaves turn yellow and premature defoliation occurs. Premature defoliation results in decreased pod production, seed fill, and/or smaller seed size. ASR can progress very rapidly and defoliate a soybean plant within four to six weeks after the initial infection. The yield loss due to defoliation will depend on the developmental stage of the soybean. The most critical stages for maintaining leaf area are the late pod (R4) to full seed (R6) developmental stages. For instance, complete defoliation during early seed formation (R5) could reduce yield more than 75 percent. There will be progressively less yield loss at earlier (R1-R4) or later stages (R6). Only after the soybean plant reaches physiological maturity (R7) will defoliation cause no yield loss.
