Infected seedlings may die pre- or postemergence. Surviving plants display systemic chlorosis on the upper side of emerging leaves, which radiates outward from the petioles. During periods of dew or rain, fluffy white growth will appear on the underside of the leaves, opposite the chlorosis. This is diagnostic and distinguishes the disease from powdery mildew (with white sporulation on the upper leaf surface), herbicide damage, and other abiotic or biotic ailments causing chlorotic leaves. If plants survive through the season, they remain extremely stunted (often 6 to 24 inches tall) and form a horizontal head with limited and nonviable seeds. While infected plants have minimal or no seed yield, adjacent healthy plants do compensate and produce larger than normal heads due to the lack of competition. Downy mildew is frequently concentrated in low/wet spots of the field, but sporadically infected plants throughout the field are not uncommon. Areas in the field with a high concentration of infected sunflower plants often appear as if they were not seeded and quickly fill with weeds.