Recognizing and Treating Powdery Mildew
Powdery Mildew is a fungal disease that can affect a wide variety of ornamental, vegetable and fruit plants. It is caused by a variety of fungal species, most with a limited range of hosts. A specie that infects roses is not likely to also infect lilacs, for example.
Environmental conditions play a large role in whether or not Powdery Mildew will be an issue from year to year, and how severe the outbreak may be. It prospers during periods of high humidity at night with low humidity during the day and temperatures in the 70-80 degree range.
Signs of Powdery Mildew
At first, symptoms appear on new leaves as small raised blisters. The leaves will curl in reaction to this. As the disease advances, leaves and unopened flower buds will be covered with a white to gray powdery growth. This will usually appear on the upper surfaces of the leaves. In advanced stages, leaves will turn brown and drop off the plant. The diseases prefers young succulent leaves over mature leaves.
Fungal spores overwinter within leaf buds and plant debris. powdery mildew fungi that spent the winter within buds resume growth into newly developing leaves shoots, flower parts, and foliage.
Plants Affected By Powdery Mildew
There are a wide range of plants affected by the various Powder Mildew specie. The most common plants are:
Annuals and Perennials
Aquillea Aster Chrsanthemum Coreopsis
Dahlia Delphinium Eupatoreum Gallardia
Helianthus Lupinus Monarda Penstemon
Phlox Pulmoneria Rudbeckia Salvia
Scabiosa Solidago Verbena Veronica
Trees and Shrubs
Amelancier Cornus Cotinus Euonymus
Potentilla Prunus Pyracantha Rose
Hydrangea Spirea Syringa Viburnum
How To Treat Powdery Mildew
- Make sure there is adequate air flow through the plants. Thinning and pruning the plants through pruning is a good way to improve the air flow.
- Don’t fertilize the affected plants until the problem is corrected. Powdery mildew favors young, succulent growth.
- When watering plants, water the root system, not the foliage. Splashing water help spread the disease.
- Choose healthy plants. Weak, sickly plants are easy targets for pests and diseases.
- Select varieties of plants that are resistant to Powdery Mildew.
- Remove plants that are perennially infected with Powdery Mildew.
- Remove fallen leaves and debris, including over the winter.
- There are several non-pesticide remedies available to treat Powdery Mildew. Look for products containing potassium bicarbonate (buy here), neem oil (buy here), sulfur (buy here), or copper (buy here)
- There are also several well-known home remedies that can be concocted from baking soda (1 tablespoon of baking soda, 1/2 teaspoon of liquid soap, 1 gallon of water) or from milk (Mix 1 part milk to 2 to 3 parts water).
- If all else fails, there are several fungicides (buy here).
- Whichever treatment you select, it will probably need to be repeated in 7-10 days.
CAUTION! Always follow label instructions when using pesticides. Please check with your local county agent or regulatory official before using any pesticide mentioned in this publication.
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