I stopped by to see Nikki Bell at the Extension office recently. Nikki is our Agricultural Natural Resource Agent for the University of Kentucky Cooperative Extension. She was working with some cucumbers plants and had applied fungicide to prevent mildew. We have at least two kinds of mildew that we deal with in these parts, powdery mildew is the most common and downey mildew on occasion.
Unlike many other fungal diseases, powdery mildew thrives in warm, dry climates, though it does require fairly high relative humidity, humidity around the plant, to spread. In cooler, rainy areas, it does not spread as well. That being said, it is capable of infecting your plants under a wide variety of conditions. When the fungus begins to take over one of your plants, the mildew that forms is made up of many spores. These spores carry the infection to other plants through the wind. Powdery mildew can slow down the growth of your plant. In some cases, if the infection is severe enough, powdery mildew can kill your plants. Plants infected with powdery mildew look as if they have been dusted with flour.
Powdery mildew usually starts off as circular, powdery white spots, which can appear on leaves, stems, and sometimes fruit. Powdery mildew usually covers the upper part of the leaves, but may grow on the undersides as well. Young foliage is most susceptible to damage. Leaves turn yellow and dry out. The fungus might cause some leaves to twist, break, or become disfigured.
The white spots of powdery mildew will spread to cover most of the leaves or affected areas. The leaves, buds and growing tips will become disfigured as well. These symptoms usually appear late in the growing season. When you see powdery mildew, you need to remove all the infected plant parts and destroy them. Remember, do not compost any infected plant, as the disease can still be spread by the wind and persist in the composted materials. Spray infected plants with fungicides. Effective organic fungicides for treating powdery mildew include sulfur, lime-sulfur, neem oil, and potassium bicarbonate.
Here are some helpful hints in regard powdery mildew. Choose plants that are resistant or tolerant to powdery mildew. Many mildew-resistant varieties of cucurbits; melons, cucumbers, squash have been developed and can be bought from major seed suppliers. Selectively prune overcrowded areas to increase air circulation; this also helps to reduce humidity around your plants. Spray your plants with fungicides according to the directions included with the products. If you don't want to use fungicides, try spraying your plants with a bicarbonate solution. Mix 1 teaspoon baking soda in 1 quart of water. Spray plants thoroughly, as the solution will only kill fungus that it comes into contact with.
Powdery mildew and August often go hand in glove. You will also see this on dahlias, honeysuckle, lilacs, privet, roses and zinnias. It arrives in late August because it overwinters in the Deep South, and its spores are blown northward every spring and summer. Mildew thrives on evenings with heavy dews. It is better to soak your plants than running the sprinkler over them. The mildew thrives on wet leaves.
It is August and I have planted my late garden. I have green beans, squash and cucumbers to name a few. If you ever try a late summer garden you will be surprised. It has been very successful for me. Happy Gardening!