Powdery mildew

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Powdery mildew
Downy and Powdery mildew on grape leaf.JPG
Example of powdery mildew (right) along with Downy mildew on a grape leaf
Causal agents: species of fungi in the order Erysiphales
hosts: plants

Powdery mildew is a fungal disease that affects a wide range of plants. Powdery mildew diseases are caused by many different species of fungi in the order Erysiphales. It is one of the easier diseases to spot, as its symptoms are quite distinctive. Infected plants display white powdery spots on the leaves and stems. The lower leaves are the most affected, but the mildew can appear on any above-ground part of the plant. As the disease progresses, the spots get larger and denser as large numbers of asexual spores are formed, and the mildew may spread up and down the length of the plant. Powdery mildew grows well in environments with high humidity and moderate temperatures.[1] In an agricultural setting, the pathogen can be controlled using chemical methods, genetic resistance, and careful farming methods. It is important to be aware of powdery mildew and its management as the resulting disease can significantly reduce crop yields.[2]

Powdery mildew growing on a leaf (magnified).
Powdery mildew growing on a leaf in high magnification.

Reproduction[edit]

Powdery mildew fungi reproduce both sexually and asexually. Sexual reproduction is via chasmothecia (formerly cleistothecium), a type of ascocarp. Within each ascocarp are several asci. Over time, ascospores mature and are released to initiate new infections. Conditions necessary for spore maturation differ among species.

Vectors of Transmission[edit]

Wooly aphids (Eriosomatinae) and other sucking insects are often vectors of transmission for Powdery mildew, and other infectious diseases. Typically wooly aphids in sub temperate climates precede and are an indicator of various infections, including Powdery mildew. Aphids penetrate plant surfaces where they often reside and provide a host of potential inoculants through physical, digestive or fecal secretions. Aphids are often an indicator of other potential plant problems.

Management[edit]

Chemical control is possible with fungicides such as triadimefon and propiconazole. Another chemical treatment involves treating with a silicon solution or calcium silicate slag. Silicon helps the plant cells defend against fungal attack by degrading haustoria and by producing callose and papilla. With silicon treatment, epidermal cells are less susceptible to powdery mildew of wheat.[3]

Milk has long been popular with home gardeners and small-scale organic growers as a treatment for powdery mildew. Milk is diluted with water (typically 1:10) and sprayed on susceptible plants at the first sign of infection, or as a preventative measure, with repeated weekly application often controlling or eliminating the disease. Studies have shown milk's effectiveness as comparable to some conventional fungicides,[4] and better than benomyl and fenarimol at higher concentrations.[5] Milk has proven effective in treating powdery mildew of summer squash,[5] pumpkins,[4] grapes,[6] and roses.[6] The exact mechanism of action is unknown, but one known effect is that ferroglobulin, a protein in whey, produces oxygen radicals when exposed to sunlight, and contact with these radicals is damaging to the fungus.[6]

Powdery mildews of various plants[edit]

Wheat, Barley and other cereals[edit]

Blumeria graminis f. sp. tritici, causes powdery mildew of wheat, whereas f. sp. hordei causes powdery mildew of barley.

Grape[edit]

Powdery mildew of grape

Erysiphe necator (or Uncinula necator) causes powdery mildew of grapes.

Onions[edit]

The fungus causing powdery mildew of onions is Leveillula taurica (also known by its anamorph name, Oidiopsis taurica). It also infects the artichoke.

Apples and pears[edit]

Podosphaera leucotricha is a fungus that can cause powdery mildew of apples and pears.

Gourds and melons[edit]

Powdery mildew of cucurbits

Podosphaera fusca is a fungus that can cause powdery mildew of Curcurbits: cucumbers, squashes (including pumpkins), luffas, melons and watermelons.

Lilacs[edit]

Microsphaera syringae is a fungus that can cause powdery mildew in lilac.[7]

Strawberries[edit]

Podosphaera aphanis is the cause of powdery mildew in strawberries and other Rosaceae like Geum rivale (the Water Avens)

Tree leaves[edit]

Sawadaea tulasnei is a fungus that causes powdery mildew on tree leaves. This fungus attacks the leaves of the Acer platanoides (Norway Maple) in North America, and in Great Britain and/or Ireland, Acer palmatum (also known as the Japanese Maple or Smooth Japanese Maple).[8]

Oregon grape[edit]

Erysiphe berberidis is a fungus that causes powdery mildew on Oregon Grape leaves. [9]

Arabidopsis[edit]

Golovinomyces orontii causes powdery mildew on Arabidopsis (rockcress) leaves.

See also[edit]

References[edit]

  1. ^ Huang, X.Q. et al. (2000). Molecular mapping of the wheat powdery mildew resistance gene Pm24 and marker validation for molecular breeding. Theoretical and Applied Genetics, 101. Retrieved from http://www.springerlink.com/content/engc84epbg6feqvk/fulltext.pdf.
  2. ^ Maloy, Otis and Debra Inglis (1993) Powdery Mildew, Washington University extension, Diseases of Washington Crops. Retrieved from http://pnw-ag.wsu.edu/smallgrains/Powdery%20Mildew.html
  3. ^ Belanger, R. r. et al. (April 2003). Cytological Evidence of an Active Role of Silicon in Wheat Resistance to Powdery Mildew (Blumeria graminis f. sp. tritici). Phytopathology, 93. Retrieved from http://www.siliforce.com/pdf/7c/Belanger-%20%20evedence%20silicon%20powdery%20mildew%20on%20wheat.pdf.
  4. ^ a b DeBacco, Matthew. "Compost Tea and Milk to Suppress Powdery Mildew (Podosphaera xanthii) on Pumpkins and Evaluation of Horticultural Pots Made from Recyclable Fibers Under Field Conditions". University of Connecticut. Retrieved 5 May 2013. 
  5. ^ a b Bettiol, Wagner (September 1999). "Effectiveness of cow's milk against zucchini squash powdery mildew (Sphaerotheca fuliginea) in greenhouse conditions". Crop Protection 18 (8): 489–492. doi:10.1016/s0261-2194(99)00046-0. 
  6. ^ a b c Raloff, Janet. "A Dairy Solution to Mildew Woes". Science News Magazine. Retrieved 5 May 2013. 
  7. ^ http://www.hfrr.ksu.edu/DesktopModules/ViewDocument.aspx?DocumentID=1662
  8. ^ Sawadaea tulasnei (Fuckel) Homma 1937 - Encyclopedia of Life
  9. ^ Pacific Northwest Plant Disease Management Handbook

External links[edit]