Powdery Mildew

Blumeria graminis sp. Tritici [teleomorph]
Oidium monilioides (Nees) Link [anamorph]

  1. Symptoms: On all hosts, the first visible symptoms of this disease are white to pale gray, fuzzy or powdery colonies of mycelia, and conidia on the upper surfaces of leaves and leaf sheaths (especially on lower leaves) (picture on left), and sometimes on the spikes. Older fungal tissue is yellowish gray (picture on right). This superficial fungal material can be rubbed off easily with the fingers. Host tissue beneath the fungal material becomes chlorotic or necrotic and, with severe infections, the leaves may die. Eventually, black spherical fruiting structures (cleistothecia) may develop in the mvcelia and can be seen without magnification.
  2. Development: The development of powdery mildew is favored by cool (15-22ºC), cloudy, and humid (75-100% relative humidity) conditions.
  3. Hosts/Distribution: The fungus has a high degree of host specificity. Isolates infecting wheat do so exclusively; the same appears to be true for isolates infecting barley, oats, and rye. Further specialization exists in the form of races. Powdery mildew occurs worldwide in cool, humid, and semiarid areas where cereals are grown.
  4. Importance: Powdery mildew can cause major yield losses if infection occurs early in the crop cycle and conditions remain favorable for development so that high infection levels are reached before heading.

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