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Stark-Billings County |
Extension Spotlites
April 24, 2008
Small Grain Diseases: Management of Those More Common and Severe in Dry Years
Small grain diseases that are more severe under dry soil conditions include wheat streak mosaic virus and common root rot. These two diseases add stress to the small grain plant which is already under stress from lack of moisture and too much heat. Wheat streak mosaic is a virus disease primarily attacking wheat crops, and is transmitted by wheat curl mites. Common root rot is caused by a fungus ordinarily found in soils, a fungus that may attack roots and crowns of wheat and barley.
Wheat streak mosaic: Wheat streak mosaic virus is carried from plant to plant by wheat curl mites. Wheat curl mites are very tiny (1/100 inch in length). Their population generally increases rapidly under extended warm dry weather, and with high mite numbers, the chance of infection of susceptible crops becomes higher. The mite transmits the virus during feeding and the virus infection causes yellow streaking of leaves, stunting of the plant, and reduced yields. The mite needs a green bridge for survival; it frequently overwinters on winter wheat or perennial grassy weeds, and then moves from these plants to adjacent spring grains in the spring or early summer.
Wheat streak mosaic is managed by two cultural practices: elimination of wheat volunteer plants and grassy weeds with herbicides (or tillage) at least two weeks prior to planting a new crop; and use of appropriate planting dates. Each practice helps to break the green bridge needed for mite survival.
Common root rot is characterized by a dark-brown discoloration of the roots, sub-crown internode, and often the crown. The disease interferes with water uptake and subsequently affects grain fill. Moist soil and cool temperatures often allow wheat and barley plants to compensate for infected roots, and yield losses may not be noticed in a cool growing season. However, early infection of roots can result in severe yield loss if the plant is subsequently exposed to high temperatures and dry soils. A diseased root system can’t absorb enough water for the plant under these stress conditions.
Three strategies are generally used to combat common root rot: crop rotation, variety choice, and seed treatment.
Crop rotation is the most effective method of reducing the risk of common root rot. Non-host crops include broadleaf crops such as soybean, canola, dry beans, and flax. Oats also are a good rotation crop if small grains must be grown.
Varieties of spring wheat, durum, and barley differ in their susceptibility to common root rot.
Several currently registered seed treatments have suppression activity against the common root rot fungus in wheat and barley. The most likely conditions where seed treatments would be beneficial are: under continuous wheat or barley production; short rotational cycles between wheat or barley; or in soils or areas where moisture stress is likely.
Also see Crop Production and Marketing
For more information contact:
Kurt Froelich,
Extension Agent
NDSU Extension Service
Stark-Billings County
1340 W. Villard St.
Dickinson ND 58601-4646
(701) 456-7665
