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RED LEAF (BARLEY YELLOW DWARF) OF OATS
By: Dale J. Gallenberg, Extension Plant Pathologist
Red leaf (barley yellow dwarf) of oats is a virus disease which also attacks barley and wheat, as well as corn, other crops, grasses and weeds. Symptoms on oats generally include stunting or dwarfing of plants along with leaf discoloration, which generally begins at the tips and extends downward. This discoloration initially appears as yellow-green spots or blotches that enlarge or coalesce, turning shades of yellow to red or purple. Diseased leaves often appear thicker and stiffer than healthy ones. Tillering and head size may be reduced, and blasting of some florets may also occur. Symptoms may not appear for several weeks following infection. Maximum symptom development occurs when heat stress follows a cool incubation period. Under very hot conditions (above 90-95oF) symptom expression slows.
Barley yellow dwarf virus (BYDV) is transmitted in the field only by aphids. A number of aphid species, including the bird cherry - oat aphid, English grain aphid, and greenbug, which attack small grains, are vectors of the virus. Some virus strains are only spread by a specific aphid vector. Attempts to control the disease through insecticidal control of the aphid vectors generally give poor results. By the time aphids are detected, infection may have already occurred. Furthermore, BYDV may be spread by those aphids escaping treatment or migrating from untreated areas.
Typically, red leaf appears in small patches or areas of a field, with only minor yield losses. However, wide-spread infections of red leaf can occur and are usually associated with the movement of viruliferous winged aphids blown north from southern areas on low level jet streams early in the season. Under such conditions, uniform infection in a field may result and yield losses may be significant. During 1987 and 1988 levels of red leaf in oats in South Dakota were very high, particularly in the southern part of the state.
In addition to distribution and numbers of plants infected, damage or yield reduction in a particular field depends on other factors, including stage of crop infection and oat variety. Infections in early stages of crop growth and development generally will result in more stunting, leaf discoloration and yield loss than later infections. Late infections may be symptomless, yet contribute to some yield loss. The primary recommendation for red leaf control in oats is early planting. With earlier planting, the crop will be at a later stage of development when and if aphids appear and infection occurs.
Oat varieties differ in their reaction to red leaf. Some exhibit less severe symptom development and yield reduction than other more susceptible varieties. Some of the better varieties in terms of response to red leaf include Don, Hazel, Ogle, Otee and Porter, although other varieties also show some resistance. Growers should consider using a resistant variety as one management tool for red leaf.
However, other factors, including yield, quality, and resistance to other diseases such as crown rust, must be considered when choosing an oat variety.
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Plant Science Department, South Dakota State University |