The Q&A Archives: Squash/zuccini disease

Question: Every year when I plant my summer squash/zuccini, they start off just fine, then the leaves get a white mold type substance on them, the fruit wethers or just rots. what is this and how can I stop it? Thanks

Answer: Donna,

The leaf mold is called powdery mildew. There are a number of options for powdery mildew control on squash. Among your least toxic options are products that contain either of the following ingredients: neem oil (not just Azadirachtin, but instead "neem oil") or potassium bicarbonate. Potassium bicarbonate is similar to baking soda (which is sodium bicarbonate). Read the label for application instructions and frequency. As a general rule, these sprays generally need to be applied on a 10-14 day basis when conditions favor powdery mildew development. Your County Extension Office can offer other options for powdery mildew control.

A fruit rot called Choanophora is probably infecting your squash. It typically starts at the blossom end of the squash and progresses on into the fruit toward the stem end. Often brown ?whiskery? growths that look like pins with black heads will appear on the end of the decaying fruit after a while. This disease is more prevalent during periods of wet, rainy, warm weather. Fungicide sprays will help, but it tends to go away on its own when the weather changes. Pick off and discard affected fruit and avoid wetting fruit and foliage when you water.

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