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Powdery mildew is a common garden disease that affects a wide variety of food crops and landscape plants. Here are several natural strategies that you can use to reduce the risk of damage from this fungal pest.
There are many different species of powdery mildew fungi, and each species only attacks specific plants. Artichokes, beans, carrots, cucumbers, eggplant, melons, parsnips, peas, peppers, pumpkins, radishes, squash, tomatoes, and turnips are all vulnerable to powdery mildew. Landscape plants, flowers, fruit trees, berries and grapes can be damaged by this fungus, too.
Powdery mildew spores typically drift into your garden on the wind, but if you’ve had powdery mildew in your garden in the past, new outbreaks may also come from dormant spores in compost or nearby weeds. This disease usually doesn’t kill plants, but it can weaken them and lead to poor growth and yield.
How to Identify Powdery Mildew
- Plants infected with powdery mildew initially show circular, powdery white spots on the upper sides of the leaves.
- These spots can then spread to the undersides of the leaves, stems, buds, and sometimes the fruit, making your plants look as if they have been dusted with flour.
- The leaves, buds and growing tips can then turn yellow and dry out, or become twisted and disfigured.
How to Prevent Powdery Mildew
As with all garden problems, prevention makes all the difference. To keep powdery mildew at bay, try these strategies:
Choose plant varieties that are resistant to powdery mildew.
Many mildew-resistant varieties of melons, peas, squash and cucumbers are available from major seed companies.
Plant in full sun.
Heat and direct sunlight inhibit fungal growth, so if your garden is shady, be sure to watch out for signs of this disease.
Give your plants ample spacing.
Follow proper spacing guidelines for your crops during planting, and as they grow, selectively prune or thin overcrowded areas to increase air circulation around your plants. Fungal diseases like powdery mildew love to make their home in densely planted, humid areas.
Water the soil, not the plants.
Splashing the leaves with water can spread powdery mildew spores. Water the base of your plants with a hose or a drip irrigation system, instead of overhead watering or using a sprinkler system. This practice can help prevent many garden diseases, and help you save water, too.
Spray neem oil weekly.
Neem oil is made from the seeds and fruit of the evergreen neem tree, and it works by disrupting the plant’s metabolism and stopping spore production. Research shows that it works best as a preventive treatment, but you can also use this after an infection has set in.
- In a small jar, combine neem oil with castile or dish soap.
- Add enough warm water to almost fill the jar, put on lid, then shake vigorously until thoroughly mixed.
- Pour the mixture into a one-gallon garden sprayer and add enough water to equal one gallon.
- OPTIONAL: Add 2 teaspoons of liquid kelp or fish emulsion to the sprayer to feed your plants while you treat them.
- Thoroughly drench the your plants’ leaves and stems weekly. (Don’t forget the undersides of your leaves!)
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Spray milk solution biweekly.
There is promising research regarding using old-fashioned milk against powdery mildew. The protein in milk appears to have an antiseptic effect when exposed to sunlight. Any fungi present are “burned” away, but, unlike neem oil, there is no residual effect beyond that. You can also use the milk spray after an infection has set in, but it works better as a preventive measure.
- Thoroughly mix liquid or powdered milk with water in a one-gallon garden sprayer.
- Since this treatment requires bright sunlight to work, drench plants biweekly, around noon, when the sun is highest over the garden.
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How to Control Powdery Mildew
Once plants are heavily infected, it’s very difficult to get rid of powdery mildew, so as soon as you see any sign of the disease, it’s important to act.
Trim off all leaves, stems and fruit with visible spots.
Discard all diseased material in the trash. (DO NOT compost infected plants because it will spread the disease.) Try not to shake the plants too much as you prune them, so as to avoid spreading fungal spores to other leaves.
Spray infected plants with organic fungicides.
Sulfur, neem oil, and potassium bicarbonate are all effective organic fungicides available at garden centers and online. Garden sulfur, in particular, has been used to treat powdery mildew on organic farms for a long time. These are most effective when used preventatively or when you first see signs of the disease.
Spray your plants with bicarbonate solution or milk spray.
If you don’t want to use store-bought fungicides. These are also most effective when used preventatively or when you first see signs of the disease.
- Thoroughly mix baking soda and castile soap with water in a one-gallon garden sprayer.
- Drench plants thoroughly every week, because the solution will only kill fungus that it comes into direct contact with.
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With careful prevention practices and these organic solutions, you can prevent and control powdery mildew from damaging your peas, cucumbers and other crops this gardening season!