In Iowa, symptoms of this disease are very noticeable after July when temperatures start to increase. Seedlings killed by Phytophthora . A brown lesion caused by Phytophthora stem rot. Stand reduction occurs when the disease infects at the seedling stage. Diseased seedlings have rotted roots and wilting in aboveground parts of the plant.
Leaves turn gray then yellow, and remain attached to the plants.
Because the Phytophthora fungus enters and colonizes on plant roots, roots of infected plants are discolored, rotten, and eventually are destroyed. Brown lesions often develop, leading from the soil line up the stem of the plant. The lesion will girdle the stem and kill the plant, and if not killed, the plant will be stunted. Infected plants often are found in circular patches in low spots of fields. Groups of infected plants also may be found scattered throughout a field.