My squash was looking so pretty; now it has some kind of fugus. What can I do to save them?
The Gardener’s Answer
Hi, Katie: It sounds like your squash has powdery mildew, a common problem among many plants. There are many different species of this fungi and each one is specific to a host plant. The species that attacks squash is caused by the fungus Erysiphe cichoracearum, which makes the foliage look like it has been covered with a white powdery substance. Severe cases cause the foliage to turn yellow and wither. This disease is more common during hot, dry conditions, which we have certainly had recently. Fortunately it does not affect the fruit. Control can be difficult after the plant has been infected. Good cultural practices are essential to prevent further spread. Making sure the squash is planted in full sun with good air circulation and planting resistant varieties is important. Fungicide applications are only a preventive measure. Once the plant is infected the fungicides will not help with the existing problem but will help prevent new infections and further spread. You should avoid using any chemicals on vegetable crops but there are organic fungicides available and horticultural oils can be effective in mild cases. Oils need to be applied at lower temperatures and, as with any product, make sure to read and follow all instructions. For now make sure to remove all foliage that is severely infected. Keep the space around your crop free of infected plant debris. A thin layer of mulch can also help prevent the spores from spreading.