Powdery Mildew
- by Holly Ciancioso
- July 25, 2024
- True Garden Blog
Why are my leaves on my cucumber plant are turning white? It is powdery mildew.
Powdery mildew is easily recognized. It is a white, powdery appearance on the upper leaf surface. It is a common fungus that tends to attack new plant growth first. While it is rarely fatal, it does spread easily and left untreated it can eventually damage the plant. The leaves will turn yellow and wither and eventually causing the plant to become weak, bloom less and slow the growth of the plant. The fungal spores can spread easily to the whole plant and to other nearby plants. The fungus thrives in high humidity (especially at night) and warm temperatures.
Some plants that are susceptible to powdery mildew are cucumbers, squash, zucchini, melons, peppers, tomatoes and parsley so keep an eye on these types of plants since it best to treat at first signs.
It is best to maintain healthy plants by removing dead or diseased foliage. Be careful to discard the diseased leaves in a bag and to not shake the leaves. Do not compost the leaves. Use a pruning shears to remove the leaves and make sure you clean the tool with rubbing alcohol after use.
Next you should treat the plant with a fungicide such as Neem oil. There are also home remedies that are effective.
Baking soda solution: Mix 1 tablespoon baking soda and ½ teaspoon liquid soap such as Castile or Dawn soap (not detergent) in 1 gallon of water. Spray liberally, getting top and bottom leaf surfaces and any affected areas. This method may work better as a preventative measure, although it does have some effect on existing powdery mildew as well.
Potassium bicarbonate: 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.
Milk: Mix 1 part milk to 2 to 3 parts water and spray liberally. While the science behind this solution isn’t fully understood, it seems to work rather well, especially on zucchini, melons and cucumbers. It is believed that naturally occurring compounds in the milk not only combat the disease, but also boost the plant’s immune system.
It is best to spray after the heat of the day. Continue to treat every 3 days until the fungus is gone.
Once plants are heavily infected, it’s very difficult to get rid of the disease so stay alert and treat at first sign of the fungus.