|
|
 |
 |
Susceptible cultivar  Resistant cultivar |
|
Control Recommendations: Wheat
Cultivars Management Practices
Wheat spindle streak virus is common in some fields in Virginia. Symptoms are typically expressed in leaves as yellow-green mottling with parallel dashes or streaks with tapered ends—hence the name wheat spindle streak. The virus is transmitted to wheat by a soil-borne fungus, Polymyxa graminis, which, in the absence of wheat, is associated with the roots of grassy weeds and other monocot crops (e.g., barley, corn, millet, rye, sorghum, etc.). Most significant infections take place during cool, wet periods in the fall. Often large areas of a field may be affected. Infection does not occur at temperatures above 68°F. The optimal temperature for symptom expression is between 48°F and 55°F. The earlier in the life of the wheat plant that infection occurs, the more severe the symptom expression. During cool spring conditions, the yellow spindle streaks may become necrotic. Affected plants may be mildly stunted and produce fewer tillers and seeds per head.
Control is affected by selecting wheat cultivars that are resistant. A list of wheat cultivar disease resistance and susceptibility is presented in the following table: Wheat Cultivars
Control of wheat streak mosaic virus
Wheat streak mosaic virus (WSMV) was observed for the first time in more than 25 years during the 2000 growing season. The incidence and severity of this disease depends on the environment, vector survival, distribution and frequency of volunteer wheat plants that serve as a source of virus and a haven for the vector, and wheat cultivar susceptibility. Symptoms of wheat streak mosaic virus typically appear in the spring. These symptoms can look very similar to wheat spindle streak caused by wheat spindle streak mosaic virus, which is vectored by the soil-borne fungus Polymyxa graminis. However, the field pattern of wheat streak mosaic is related to the distribution and activity of the vector, the wheat curl mite, Aceria tulipae. As the wheat crop develops, plants affected with WSMV are typically severely stunted with yellow mottled and streaked leaves. These yellow streaks are often seen as discontinuous dashes running parallel to the leaf veins. As the season progresses, plants affected and colonized by the curl mites may develop "leaf rolling." Leaves appear upright while the margins roll inward. This symptom of mite feeding looks like drought stress in the affected plants. Wheat streak mosaic symptoms tend to become more severe as the weather warms, and severely affected plants may produce sterile heads or die prematurely.
The wheat curl mite, Aceria tulipae, is the vector and the only means by which the virus is transmitted in nature. This mite thrives in lush young growth of wheat and other grasses. Thus, volunteer wheat in soybean fields harvested in the fall is a particularly good breeding ground for this mite and the virus. The wheat curl mite is approximately 0.03 mm long. It is invisible to the unaided eye and is easily dispersed by winds. The mite can develop from egg to adult in 8 to 10 days. It reproduces rapidly at temperatures ranging from 75°F to 80°F. Dry conditions also favor the mite’s development. It can overwinter as an egg, nymph, or adult either in the crowns of wheat plants of other host grasses. This enables the mite to survive freezing temperatures for several months. Survival is even greater in mild winters. Although wheat is the preferred host for Aceria tulipae, many other species of grasses are hosts for both the mite and the virus. These include corn, oats, foxtail, barnyardgrass, and others. Volunteer wheat is the primary means by which the wheat curl mite populations and the wheat streak mosaic virus are maintained. In the absence of a host with live green leaves, the wheat curl mite will only survive for a few days.
Since there are no effective chemicals registered for control of the wheat curl mite, disease management should be directed toward removing host plants during the fall and winter months (e.g., volunteer wheat) to prevent the survival of the mite and the maintenance of the virus in or near the field. Cultivars can vary in their susceptibility to the virus, but at this time the resistance or susceptibility of soft red winter cultivars has not been adequately characterized.
Control Recommendations: Wheat Cultivars Management Practices
| Disease Management Practices | Foliar Diseases | Seed and Seedling Diseases | Root and Crown Diseases | Head Diseases | Virus Diseases |
