Powdery Mildew and Other Fungal Diseases

Not many gardeners have gone a season without some powdery mildew. Even in dry areas, a sprinkler gone awry can cause this fungus to seemingly creep over a garden and destroy it in days. We got this tip for keeping powdery mildew under control from the keynote speaker Tane Datta at CTAHR’s  Organic Gardening Workshop.

Remember that powdery mildew is a fungus that usually appears as a white or gray powder on tops of leaves. The first sign is usually twisting and curling of young leaves on the lower part of the plant. You usually see it on beans, cucumbers, melons, mangos and squash but we’ve seen it on tomatoes and many ornamentals too. Although it rarely kills a plant, it causes poor growth and lower yields.

Prevention is the easiest way to manage any fungi by ensuring plants are healthy, get enough sunlight and have good air circulation. If you have had problems before, choose mildew resistant varieties. Make sure not to overfeed your plants as this severely stresses them.

Fungi spreads from the spores being flown around by wind or from just growing from one plant to another. Spores can live in the soil for a long time.

Always make sure to sanitize (remove) really bad areas. Be careful to not shake the foliage as that will spread the spores. It is ok to put plants with powdery mildew in your compost pile as long as the pile gets hot. Otherwise, discard in a sealed plastic bag.

So here’s the big tip — don’t try to treat Powdery Mildew the same way each time. Mix up different types of treatments and you’ll have a lot more success! Here are a few of the organic methods people report having success with.

  • Spray liquid seaweed onto your plant’s leaves. Research has shown that this has a powerful “booster” effect to your plant’s health and it helps fight off the powdery mildew.
  • Sulphur sprays are quite effective at stopping the spread of powdery mildew. They also destroy beneficial soil fungi as well so don’t spray too much.
  • Mix 1 heaping tablespoon of baking soda, 1 tablespoon of dormant oil, and ½ teaspoon of insecticidal or dish soap in one gallon of water.
  • Mix cow’s milk at a ratio of one part of milk to nine parts of water and spray weekly.
  • Pour one part of standard 3 percent-strength hydrogen peroxide with three parts water. Spray on plants daily until mildew subsides.
  • Kaligreen® is an organic solution with potassium Bicarbonate. Mix according to instructions.
  • SERENADE® is another organic product that comes in both a powder and liquid.
  • There are also fungicidal products on the garden center shelves featuring jojoba oil and neem oil.
  • Here a new one… one of the most effective measures in preventing and treating powdery mildew is to spray the foliage of your plants daily with plain water from the hose. Powdery mildew hates water! The only caveat with this method is to be sure you do it early in the day so that the foliage completely dries before cooler evening temperatures arrive, otherwise you may invite other fungal diseases, such as black spot, into your garden.

Happy Gardening
Reposted from South Maui Sustainability.org blog.

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