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.

Powdery Mildew on Lilac

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.

Lifecycle

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

Zinia

Trees and Shrubs

Amelancier                         Cornus                                  Cotinus                                                 Euonymus

Potentilla                             Prunus                                  Pyracantha                                         Rose

Hydrangea                          Spirea                                   Syringa                                                 Viburnum

How To Treat Powdery Mildew

Powdery Mildew on Lilac

Cultural Control

  • 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.

Chemical Control

  • There are several non-pesticide remedies available to treat Powdery Mildew. Look for products containing potassium bicarbonate, neem oil, sulfur, or copper
  • 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 available at your local garden center.
  • 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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