How to Manage Pests
UC Pest Management Guidelines
Pathogens: Each type of small grain is attacked by a specific form of the fungus Blumeria graminis (Erysiphe graminis): Erysiphe graminis f. sp. tritici infects wheat; Erysiphe graminis f. sp. hordei infects barley and weeds in the genus Hordeum; Erysiphe graminis f. sp. avenae infects oats and wild oats
(Reviewed 2/07, updated 2/09, pesticides updated 7/16)
In this Guideline:
The disease first appears on lower leaves: white, cottony patches of fungal growth on the upper leaf surface that are opposite chlorotic spots on the underside of the leaf. The patches of white growth turn a dull gray-brown as fruiting structures, called cleistothecia, develop. Plants are often low in vigor.
The fungus overwinters in tiny, dark, spore-forming structures called cleistothecia that release airborne spores (ascospores) in spring. It also can overwinter as mycelium on volunteer wheat, barley, or oat plants and produce spores (conidia) that can cause initial infections; conidia from resulting lesions are windblown for secondary disease cycles at 10-day intervals. Disease development is optimal at 59° to 72°F (15° to 22°C) and is retarded above 77°F (25°C). Disease is favored by dense stands, high nitrogen fertilization, high relative humidity, and cool temperatures.
Resistant cultivars of barley and wheat are available (see BARLEY and WHEAT CULTIVAR TABLES). Crop rotation, elimination of crop residue, and control of volunteer grains and weed hosts reduce inoculum survival from one season to the next.
Although normally not economical, foliar fungicides can be used to control disease outbreaks and provide partial disease control. Applications should be made between tillering and heading with the objective being to protect the flag leaf. Depending on weather conditions from tillering to early dough stage, one or more applications may be needed.
UC IPM Pest Management Guidelines:
R. M. Davis, Plant Pathology, UC Davis