How to Manage Pests
UC Pest Management Guidelines
Infections begin as irregular yellow patches on leaves; these chlorotic lesions later turn tan to light brown. If conditions are favorable, white fluffy growth of the fungus develops on the undersides of leaves. If disease development is extensive, leaves may take on a blighted effect as a result of numerous infection sites. Systemic infections can cause internal black streaks and patches to form in stems and floret branches of broccoli and cauliflower. Early symptoms on transplants may resemble bacterial leafspot symptoms. Severely diseased seedlings may be stunted or die.
Peronospora parasitica requires cool, moist weather for infection and disease development to take place. The pathogen survives between crops on weed hosts or as resilient oospores in crop residue. Spores are airborne. This disease is most serious on young seedlings; if cotyledons and the first true leaves are severely infected, the young plant may die.
A few broccoli varieties are available that are resistant to downy mildew. Fungicide treatment of susceptible varieties is needed when the disease occurs on transplants or early in crop development in the field; repeated applications may be required, depending on weather. Treatment during early flowering is required on seed crops.
Organically Acceptable Methods
UC IPM Pest Management Guidelines: Cole Crops