Powdery mildew looks like a grey powder-like substance on all of your leaves.
Powdery mildew is the common name for a number of species of fungus that negatively affect your plant leaves. It’s spread by wind and often overwinters on plants. Watch for it in the warm days and cool nights of late summer. Your crops usually won’t die from powdery mildew, however it may affect the flavor, yield, and aesthetics of your crop.
How Plants Get Powdery Mildew
Powdery mildew is most frequent when you water your squash plants from the top, resulting in wet leaves. Powdery mildew is also bad when relative humidity is high around the plants, even if the leaves aren’t getting wet. Most frequently, relative humidity gets high when plants are spaced too closely together and aren’t thinned properly.
- Use drip irrigation instead of hand watering. If hand watering, avoid the leaves!
- Plant where there is good air circulation, and thin to the recommended number of crops per square.
- Sunny locations help inhibit spore germination.
- There are many mildew-resistant or mildew-tolerant strains of plants.
- Selectively prune overcrowded plant material to help increase air circulation. Prune off the leaves that are getting hit the worst. This helps reduce relative humidity and infection (don’t compost them!)
- To take direct action against powdery mildew, spray affected crops with a mixture of 1/4 cup of milk and 1 quart of water.
- Anti-Fungal Baking Soda Spray
- For plants that already have powdery mildew – hose down all the infected leaves prior to treatment. This helps to dislodge as many of the spores as possibly to help you get better results. Use as prevention or as treatment at first signs of any of the diseases.
- To make: Mix 1 tablespoon baking soda, 2 1/2 tablespoons vegetable oil with one gallon of water. Shake this up very thoroughly. To this mix add 1/2 teaspoon of dishwashing soap and spray.
- This won’t get rid of the fungus on leaves that already have it, but it will prevent it from spreading to the rest of the plant.
- Repeat every 5-7 days as needed