 The soybean plant has an age-related resistance in which the older leaves are not susceptible to foliar blight.Soybean fields infected with "Phytophthora sojae" can be easily spotted by looking for stunted soybean plants or looking for empty patches where the soybean seed had been planted.Microscopic identification of an oospore that measure around 40 micrometers in diameter from a soybean plant sample is a definite sign of "Phytophthora sojae".