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Powdery Mildew

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Powdery mildew of cucurbits

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 mildews of various plants

Example of powdery mildew (right) along with Downy mildew on a grape leaf

Powdery mildew of grape

Powdery mildew of grape

Erysiphe necator (or Uncinula necator) causes powdery mildew of grapes. It produces common odors such as 1-octen-3-one and (Z)-1,5-octadien-3-one.

Powdery mildew of wheat

Blumeria graminis forma specialis (f. sp.) tritici, causes powdery mildew of wheat. It can persist between seasons most likely as ascospores in wheat debris left in the field. Wheat mildew thrives in cool humid conditions. Though present throughout wheat growing regions it especially favors the eastern seaboard of the United States as well as coastal regions of the United Kingdom. Controlling the disease involves eliminating conducive conditions as much as possible by altering planting density and carefully timing applications and rates of nitrogen. Since nitrogen fertilizers encourage dense leafy growth, nitrogen should be applied at precise rates to control decrease severity. Crop rotation with non-host plants is another way to keep mildew infection to a minimum, however the aerial nature of conidia and ascospore dispersal makes it of limited use. Chemical control is possible with fungicides such as triademefon and propiconazole. In addition, control of powdery mildews is possible using cultivars containing R genes (resistance genes) to prevent infection.

Powdery mildew of onions

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

Powdery mildew of apples and pears

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

Powdery mildew of gourds and melons

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

Reproduction

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.

See also

• Erysiphales
• Oidium (genus)
• Powdery mildew (barley)

Wikibooks' A Wikimanual of Gardening has more about this subject: Powdery Mildew

References

1. ^ [1]

External links

Wikimedia Commons has media related to: Powdery mildew

• About Erysiphe necator
• Powdery Mildew and Lawn Care
• SAFECROP - Proceedings of the 5th International Workshop on Grapevine Downy and Powdery Mildew

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