Powdery Mildew

Mar 27, 2014

Watch for powdery mildew!

When to look for it – This white, powdery-looking stuff usually appears on leaves starting in July.  Some of the most commonly hit plants are Phlox, Bee Balm, Heliopsis, Zinnias, and Lilacs.

Why it happens – Powdery mildew thrives in locations where there is poor air circulation, overhead watering (especially inconsistent watering), and hot weather. Powdery mildew will rarely kill plants but it will make them look yucky. 

What To Do About It – Strip off infected leaves and get rid of them (do not put them in your compost pile). If the plant is a real mess, cut the whole thing down to within 3”-5” of the ground – new growth is typically not infected.

Prevention – To reduce powdery mildew in your gardens, open up space around your plants by divisions and/or weeding water from below (i.e., soaker hoses); if watering from above then water in the morning so leaves are dry by nightfall. Buy mildew-resistant plants (there are now quite a number of varieties available). There are effective organic products that address fungal diseases. Neem Oil, Bon-Neem and Serenade are all terrific picks. You can also spray the leaves of mildew-prone plants each year BEFORE you see any signs of problems.

Home Remedies – Starting in early May, and then every two weeks, spray one of the following two solutions on the upper and lower surfaces of the leaves:  Baking soda and water – one teaspoon of baking soda and 3-4 drops of liquid dish detergent or Murphy’s oil soap to one quart of water. Milk and water – one part whole milk to two parts water.  Shake well and apply. Either method will work.

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