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Example of downy mildew (left) along with powdery mildew on a grape leaf
Unidentified species of mildew growing on a plastic shower curtain.  The numbered ticks on the scale are eleven (11) microns apart.

In horticulture, mildew is fungi in the order Erysiphales. It is also used more generally to mean mold growth.

In Old English, it meant honeydew (a substance secreted by aphids on leaves, formerly thought to distill from the air like dew), and later came to mean mildew in the modern sense of mold or fungus.[1]


Plant pathogens

What horticulturalists and gardeners often refer to as mildew is more precisely called powdery mildew. It is caused by many different species of fungi in the order Erysiphales. Most species are specific to a narrow range of hosts, and all are obligate parasites of flowering plants. The species that affects roses is Sphaerotheca pannosa var. rosae.

Another plant-associated type of mildew is downy mildew. Downy mildews are caused by fungus-like organisms in the family Peronosporaceae (Oomycota). They are obligate plant pathogens, and the many species are each parasitic on a narrow range of hosts. In agriculture, downy mildews are a particular problem for growers of potatoes, grapes, tobacco and cucurbits.

Household varieties

The term mildew is often used generically to refer to mold growth, usually with a flat growth habit. Molds can thrive on many organic materials, including clothing, leather, paper, and the ceilings, walls and floors of homes or offices with poor moisture control. There are many species of molds. The black mold which grows in attics, on window sills, and other places where moisture levels are moderate often is Cladosporium. Color alone is not always a reliable indicator of the species of mold. Proper identification should be done by a microbiologist. Mold growth found on cellulose-based substrates or materials where moisture levels are high (90 percent or greater) is often Stachybotrys chartarum and is linked with sick building syndrome.[2] “Black Mold,” also known as “Toxic Black Mold,” properly refers to S. chartarum. This species commonly is found indoors on wet materials containing cellulose, such as wallboard (drywall), jute, wicker, straw baskets, and other paper materials. S. chartarum does NOT grow on plastic, vinyl, concrete, glass, ceramic tile, or metals. A variety of other mold species, such as Penicillium or Aspergillus, do. In unaired places, such as basements, molds can produce a strong musty odor.

The English word was exported into French as mildiou and as mildiu or moho in Spanish.[3]

See also


  1. ^ The American Heritage Dictionary of the English Language, 1969, entry "melit-" in Appendix
  2. ^ "Smelly Moldy Houses".
  3. ^ "Mildiu".

External links