Biology
Downy mildew is a fungal disease typically found on leaves of broccoli, cabbage, and other plants in the mustard family including weeds. Leaves first show pale green to yellowish spots on the upper surface which turn more yellow as they enlarge. The underside of infected areas later develop grayish to white fungal growth. Stems of broccoli may also be affected, showing spots on the outside and brown to purple streaks internally. Heads of broccoli and cauliflower may be dark brown or black inside, while cabbage heads may show small, sunken, black spots. Downy mildew development is favored by cool, humid weather.
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