About this time of year, late summer and early fall, a white fungus begins to develop on squash, cucumber, and melon leaves. Do be aware that it could try other plants, too. There are many types of this fungus.
It looks like little white dots on the leaf, but if it spreads, it appears like a white powder has been sprinkled onto the leaf. It can also be found on the leaf stem.
Powdery mildew loves warm, dry climates with fairly high humidity, poor circulation, and little sunlight.
If severe enough, the leaf will turn yellow, and photosynthesis cannot occur. This may not kill the plant outright, but will cause problems such as the plant becoming weak and growing slower with less blossoming.
Make sure there is plenty of air circulation between plants, walls, and plants.
Follow plant tag directions for the amount of sunlight. Wind carries spores from one plant to another, so keep on top of it. Kill it or remove it if badly infected.
If the leaf and or vine is heavily infected, you should remove them and burn them or throw them into the trash. DO NOT put them into compost!
There are fungicides that, when sprayed or brushed on, will kill it. Some may even be approved for organic gardening. If you don’t want to use a commercial fungicide (if you prefer an organic type of approach), then there are several things to try:
1) Milk, of any dilution, seems to work the best. 1 part milk to 2 or 3 parts water. (I’ve read about and used different ratios. Ex: 1 to 5, or 1 to 6, even 1 to 10, but try and see what works for you in your circumstance.)
2) Others are less effective, such as:
- Mix 1 tablespoon baking soda and ½ teaspoon liquid soap such as Castile Soap (not detergent) in gallon of water. Or mix 1 tablespoon potassium bicarbonate and ½ teaspoon liquid soap (not detergent) in 1 gallon of water.
- Spray liberally to all affected areas. This mixture may work better than baking soda as a treatment for existing infections. (One can mix both together, and add some neem oil, if desired). These mixes may help more in preventing that killing powdery mildew.