Controlling Powdery Mildew on Vegetables

Every summer it seems to appear; white, powdery spots all over the leaves and stems of your vegetables. While it is rarely fatal, it can weaken susceptible plants and reduce vegetable and flower production. So what is that stuff exactly? 

Powdery mildew is one of the most widespread fungal diseases of plants, and also one of the easiest to identify. It appears as white or grey spots covering most or all of the surfaces of leaves. In the advanced stages, leaves can turn yellow, curl up, and drop off. This leads to stressed plants and reduced flower production. 

While it’s ideal to avoid an infestation by growing resistant varieties of plants, making sure your plants are in full sun, and preventing over-fertilization and crowding, there are things you can do to control powdery mildew that is already present. 

There are many commercial options for controlling mildew growth on plants. In particular neem oil is one of the many horticultural oils labeled for the control of powdery mildew as well as a number of other diseases. 

If you’re more of a DIY gardener, baking soda combined with dormant oil and liquid soap is also known to be helpful in the early stages of an infestation and will inhibit mildew growth.

In the very early stages, plain water will knock fungal spores off the plant before they can embed. Just be careful because wet plants can become the victims of a whole other host of diseases. When you water plants for this purpose, do so early in the morning so that the sun can burn off the water throughout the day. 

Potassium bicarbonate, which is similar to baking soda, is a contact fungicide that will kill powdery mildew spores on contact. 

Mouthwash mixed with water (in a one-to-three ratio) can eliminate mildew growth. Just be careful as it can burn new plant growth. 

Two to three tablespoons of apple cider vinegar mixed with a gallon of water can also be an effective anti-fungal treatment. 

These are just a few of the treatments available for powdery mildew. When treating an affected plant be sure to spray the entirety of the affected leaves including the underside of leaves. 

After treatment, you may want to trim off some of the most infected leaves so that the plant can put energy into new growth rather than into old damaged leaves. If you do go that route, you can take the plant debris and throw it away. You don’t want to put powdery mildew and its spores in your compost, as they can overwinter and spread to your plants next season.