Organic Ways to Kill Powdery Mildew
Plants most susceptible to powdery mildew
What is the Powdery Mildew on My Plants Leaves?
As a former landscaper, I have seen a lot of plant diseases. One of the easiest ones to recognize is powdery mildew; it looks just like its name. The mildew will form a white or gray powdery film on a plant's leaves, stems, and fruit.
Powdery mildew is a fungal disease caused by the many varieties of the fungi which belong to the order Erysiphales. The fungus thrives in warm, humid environs, and overwinters in the soil. It is spread by the wind, insects and water run-off.
According to the Arizona Cooperative Extension, "Unlike most fungi, spores germinate on the surface of plant parts without the presence of free water."
Where does powdery mildew start?
The mildew usually starts on a plants lower leaves, and if the fungus is not treated it will spread over the entire plant. When the leaves become severely covered with the fungus, photosynthesis will be affected and leaves will yellow and drop off. As a result, the plant may become so stressed it will not flower and/or fruit with any vigor.
Are all forms of the fungus the same?
There are many forms of powdery mildew, and each is species specific. Grapes will suffer from the powdery mildew that affects only grapes, roses suffer from rose powdery mildew, and so on.
Although all plants can get the fungus, certain species are more susceptible to it.
If your plant has a black sooty substance on its leaves, it may be sooty mold. You can find information on that here: What is the Black Soot on my Gardenias?
How Can I Prevent Powdery Mildew?
Preventing the spread and/or severity of powdery mildew is the most cost effective way of dealing with the fungus. Try the following tips if you are battling the fungus in your garden and flower beds.
Buy mildew resistant varieties
There are a large variety of hybrid plants that are resistant or tolerant to the growth of powdery mildew. The resistant plants will be less likely to develop the mildew. The tolerant plants will show fewer ill effects of an infestation of the fungi.
Do not crowd plants
Good air circulation ensures lower humidity levels, inhibiting the growth of powdery mildew. Crowded plants will also provide too much shade for the lower leaves, encouraging fungi growth.
Do not grow susceptible plants in the shade
Although powdery mildew prefers warmth, it does not tolerate high temperatures. Plants that are shaded much of the day will stay cooler, encouraging the growth of mildew.
Dispose of infected leaves and stems
Never use the infected plant leaves or fruit as mulch. Trim off infected leaves and stems and dispose of properly. If your municipality allows backyard fires, then burn the debris. If not, dispose of the debris according to your local plant disposal regulations.
Water the soil, not the plants
While the water will not encourage mildew growth, splashing the leaves with water will spread the spores. Run a hose to the base of your plants instead of using a sprinkler system.
Potassium Bicarbonate Organic Fungicide
What are the Organic Treatments for Killing Powdery Mildew?
When treating your plants, make sure the leaves are coated with the solution. Reapply weekly unless otherwise specified on a products label.
Numerous studies have shown milk and/or whey to be an effective anti-fungicide. The milk and whey are believed to produce free radicals which are toxic to the fungus.
Mix 60 parts water with 40 parts milk or whey and spray onto the affected plants bi-weekly.
Mix one oz powdered milk to 2 liters of water.
Baking soda changes the pH of the fungus and kills it.
Mix 1 tbs of baking soda and 1/2 tsp liquid hand soap with one gallon of water.
Spray solution on affected leaves, and dispose of any remaining solution. Do not apply during daylight hours. It may be best to test one or two leaves to see if the solution will cause the plant to suffer sunburn.
Potassium bicarbonate is a safe, effective fungicide. It is used as a leavening agent, and is used in wines and bottled waters.
Mix 3 tbs potassium bicarbonate, 3 tbs vegetable oil and a half teaspoon soap iinto a gallon of water.
Sulfur is a natural product that is very effective at preventing and controlling powdery mildew. Sulfur can be bought as a dust, or as a liquid which can be added to sulfur vaporizers.
Follow the dosing instructions closely and wear gloves, eye protection, and a face mask. Avoid inhaling or coming into contact with the sulfur .
Neem oil is made from the seeds and fruit of the evergreen neem tree. Neem oil works by disrupting the plants metabolism and stopping spore production.
Mix 3 tbs of neem oil to one gallon of water.
Take precautions to avoid sunburn of leaves, and avoid spraying the plant's buds and flowers.
Copper is a very effective fungicide, but it is very important to follow label directions closely. Too much copper will be detrimental to the plant and the soil.
Vinegar is very acidic. When sprayed on powdery mildew it changes the fungi's pH, effectively killing it.
Mix 4 tbs of vinegar with 1 gallon of water. Reapply every three days.
Garlic has a high sulfur content and is an effective anti-fungicide. Garlic oil can be bought commercially if you do not wish to make the solution at home. Garlic works best when added to organic oil mixtures.
Crush six cloves and add to one ounce of an organic oil such as neem oil and one ounce of rubbing alcohol. Let set for two days, then strain and retain the liquid and crushed garlic. Again soak the garlic, this time in one cup of water for a day. Strain out and dispose of the crushed garlic. Add the oil and alcohol mixture and garlic water to one gallon of water. Spray your plants, coating only the leaves.
Interesting gardening links
- Powdery Mildew
Most powdery mildews are recognized by the white to gray, powdery spots or large blotches on the surface of leaves, stems and fruits of host plants. T
- How to Treat and Prevent Blackspot Disease on Roses
Blackspot disease is a common problem on roses and other plants. Learn about the natural and chemical treatments that will keep your roses healthy and beautiful.
- What Is the Orange Fungus Growing in My Mulch?
Something may be hiding in your mulch. Something which may make you ask, "What is the orange fungus growing in my mulch?" The answer is not what you expect.