Signs and Symptoms of Powdery Mildew Disease

Mycrosphaera pencillata Mycelium on Leaves of Azalea
Powdery mildew is a disease that causes minimal long-term damage to trees in a forested environment. The forestry industry has traditionally dismissed the impact of this disease as a problem due to its minor effect upon the economic value of  harvested stands. It is, however, a very real concern to growers of ornamental woody and herbaceous perennial plants, annuals, vegetables, fruits, grains and turf grasses. Within these industries, powdery mildew causes economic loss by weakening plants, promoting poor growth, and decreasing yields. In ornamental plants, powdery mildew detracts from the value of plants through the malformation and discoloration of leaves, destruction of fruit and flowers and overall decreased plant growth.

Powdery mildew disease is so common, widespread, and ever-present that the total losses in plant growth and crop yields most likely surpasses those losses caused by any other singular plant disease. Powdery mildew fungi do not typically kill their host, but instead interfere with normal plant growth by utilizing the host's nutrients, decreasing photosynthesis, increasing respiration, and increasing transpiration.

Signs and Symptoms of Powdery Mildew Disease

Microsphaera alni Cleistothecia on Oak Leaf (Quercus sp.) Microsphaera syringae On Lilac (Syringa vulgaris)

  • older lesions turn brown and appeared shriveled
  • mycelium of fungus forms mats and appears as white, grayish white or tan colored patches on leaves, buds, stems or young fruit
  • fruiting bodies (cleistothecia) appear as small black or brown specks on the mycelial mats
  • infected leaves often appear chlorotic due to decreased photosynthesis
  • leaf curl
  • leaf drop
  • infected fruit and flowers are often aborted or malformed
  • early signs include small chlorotic spots or blistering on leaves or flowers
  • Podosphaera clandestina Cleistothecia on Cherry Leaf x30 (Prunus sp.) Chlorotic Lilac Leaf Uncinula salicis on Weeping Willow (Salix babylonica) Blumeria graminis on Barley

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    Minor formatting & link modificaitons 31 January 2008 by M.J. Munster