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Powdery Mildew on Cucumbers, Squash and Other Vine Crops

Yellow spots and a white powdery substance on the leaves of cucumber, squash, and other vine crops are symptoms of powdery mildew fungal disease.

You’ll often find the plants that have started fruiting are the first to be infected. The infected leaves eventually turn brown and die. The fruit are rarely infected with this disease, but severe infestation can reduce the size and number of fruit produced.

Consider using an ecofriendly control if treatment is needed. Cornell University found a mixture of 1 ½ tablespoons of baking soda and 3 tablespoons of light weight horticultural like Summit® Year-Round® Spray Oil mixed in a gallon of water was effective at controlling this disease.  Light weight oils alone have also proven effective.  You will need to apply most products every 7 to 14 days as soon as you discover the disease. As always read and follow label directions carefully. 

A bit more information: Reduce future problems with proper planting and sanitation.  Give plants plenty of room to reach their mature size. This increases air flow and light reaching the plants, decreasing humidity and the risk of infection.  Try training fruit up a vertical support. You’ll not only save space, but also increase light and air penetration around the plants for greater productivity and less risk of disease.


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