Clemson Plant Pathologist Tony Keinath reports in the The South Carolina Grower that conditions are favorable for downy mildew disease to start on collards and kale.
Control methods must be effective to increase crop yields. Keinath recommends the following practices to maximize control:
- Rotate crops to new fields every year, since downy mildew disease in brassicas can survive in the soil.
- Check older leaves for angular yellow downy mildew spots on the top of the leaves and black lesions with white downy mildew growth on the bottom of the leaves. Lesions as small as 1/8-inch in diameter can produce spores.
- Since foggy fall mornings are warning signs that conditions are favorable for disease development, make the first fungicide spray when the first foggy morning is predicted. Fog leads to the leaves remaining wet all night and for a good portion of the morning.
- Potassium phosphite is a very effective, economical alternative fungicide, though it is not labeled for certified organic production.
- Rotate effective conventional fungicides like Zampro or Presidio with potassium phosphite during rainy periods.
For more info on brassica downy mildew, see Dr. Keinath and Tim Bryant’s article in the latest issue of the Clemson IPM Newsletter.