Garden Journal

Organic methods can kill powdery mildew

May 29, 2013

Scram! Get lost! Or the once popular “take a powder” (supposedly from a doctor prescribing a powder to get rid of a patient) all tell us to leave. Now that the garden is up and growing, you may find something that you wish would “take a powder.” This disease looks like a fine powder or dust on leaves. It is powdery mildew (Podosphaera Xanthii), which is a fungal disease. It is most common on vegetables such as cucumbers, peas, pumpkins, squash and melons, and flowers such as phlox, lilac and roses.

This disease doesn’t just look bad, it is a real killer. Often the leaves are twisted and stunted and fruits are misshapen. Powdery mildew can sometimes weaken a plant so much that the plant dies.

Wind spreads powdery mildew spores. Even though powdery mildew can pop up anywhere, it is most common in shady areas with poor air circulation and high humidity. Avoid high-potency fertilizer which can cause a burst of new, but weak growth that is more susceptible to attack.

You can choose mildew-resistant varieties such as the phlox David, and Honey Bear acorn squash. Plant vine crops such as melons and cucumbers where they will get plenty of sunshine. Don’t overcrowd your plants, so air can circulate freely Prune any extra leaves. Always water plants at ground level and be careful that water doesn’t splash up onto the leaves and stems.

You can fight powdery mildew organically and safely. Milk contains salts and amino acids that are helpful to plants and also combat powdery mildew.

Make your own spray by blending one cup of skim milk with nine cups of water. Spray this milk and water mix onto the infected leaves every two or three days. You can also use baking soda (bicarbonate of soda) as a safe organic spray. Add one tablespoon of baking soda to one gallon of water. Spray every two or three days.

Better than baking soda is potassium bicarbonate, which really knocks out powdery mildew and eliminates it completely.

Many nurseries sell organic Neem oil that will attack many plant-borne fungus diseases. Neem oil is extracted from the Neem tree of India. To use Neem oil, mix two tablespoons of oil and a dash of dish detergent in a gallon of water.

And finally, you can even use mouthwash to kill the fungal spores of powdery mildew. Try plain, inexpensive ethanol-based mouthwash mixed one part mouthwash to three parts water, and spray this on the affected areas every two or three days.

To prevent more spores from blowing around the garden always remove all dead leaves, twigs and flowers from the garden. The spores can live over the winter in dead plant material. Bag the infected plant material and toss it out or burn it. Never compost infected plants, as you can just spread the disease.

At the first sign of powdery mildew, reach for the milk or the mouthwash or Neem oil. These organic safe treatments will, like a kindly doctor, cause powdery mildew to “take a powder.”

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