All aboveground plant parts may be affected and young leaves are especially sensitive, from where the pathogen grows into the crown. Large, light green leaf spots develop on the upper leaf surfaces. Under moist conditions, a white to gray mold appears on the lower or upper leaf surfaces. Affected leaves may wilt, and then die. If environmental conditions become unfavorable for downy mildew, plants may show recovery by developing healthy leaves, or other pathogens may be encouraged. During fall wet periods, most young petioles or leaves are covered with a fungal growth that often moves into the crown. Crown infection causes excessive leaf proliferation, which in turn causes misshapen bulbs.
Plant Protection Products