Oats are subject to a large number of diseases that can cause severe damage to quality and reduce yields. The most common diseases that effect yield are crown rust, stem rust and barley yellow dwarf virus. (View chart of leaf diseases and treatments.)
Crown rust generally is the most widespread and destructive disease of oats the eastern prairies. Crown rust can reduce yields, lower test weights and groat percentage, and increase lodging. This disease is caused by the fungus Puccinia coronata. Spores are blown in from winter oat-producing regions in the southern US. Crown rust is identified by the pustules producing yellow-orange spores that infect leaves primarily. As the crop approaches maturity, a black spore stage may also be found on the oat leaves, appearing as a black or dark brown ring around the yellow-orange pustules.
Growing varieties with resistance is the most effective and economical method of controlling crown rust. However, the crown rust fungus can quickly develop new races that are able to attach the genetic resistance varieties that is available. Therefore, resistant varieties become susceptible to crown rust as new races develop. Refer to the latest oat variety selection guide to select varieties resistant to prevalent races of crown rust.
Seeding early will allow the crop to develop past the most susceptible stage in the areas where the risk of crown rust is lower. This is due to the fact that it takes longer for the rust spores to blow in from the south and east in these areas.
A number of fungicides are registered for use on oats that can control crown rust and other foliar diseases. Consider applying fungicide when the yield potential and value of the crop is high, when leaf diseases developed early in the season and the long-range forecast is for continued moist weather. Fungicides should be applied to protect the flag leaf. The best time to apply fungicide is at the late flag leaf to boot stage (Feekes 9.0 – 10.1). Refer to the most recent edition of provincial Crop Protection Guide for details of the registered products.
Stem rust epidemics are infrequent on the Canadian prairies, but they have the potential of being serious in southern Manitoba if oats are planted late and winds occur that blow spores in from the south. Stem rust is caused by the fungus Puccinia gaminis f. sp. avenae. The major source of infection is from spores blown up in summer winds from southern US where winter oats are grown.
Stem rust and crown rust are distinguished fairly easily on the basis of spore color. Stem rust spores are more brick red, while crown rust spores are a bright yellow orange. The red-rust spores of stems rust also are carried from diseased plants to nearby plants via wind. These spores are replaced with a mass of black spores later in the season.
Control of stem rust, as with crown rust, is most economically accomplished by using resistant varieties. Refer to the latest selection guide to determine the level of resistance in available varieties to the prevalent races of stem rust. Stem rust resistance in oat varieties is generally more stable than crown rust resistance. Stem rust can be controlled with fungicides. Refer to the most recent edition of provincial Crop Protection Guide for details of the registered products.
Barley Yellow Dwarf
Barley yellow dwarf (BYD) is a virus that can cause significant yield loss in oats in western Canada. As the name implies, the barley yellow dwarf virus also infects barley as well as wheat. It is transmitted from plant to plant by several species of grain aphids. These aphids usually acquire the virus when feeding on infected plants in the southern half of the U.S. and then are carried to northern oat fields in winds and by storm fronts. The disease potential greatly depends on the northward movement of these aphids from southern fields.
Barley yellow dwarf-infected plants normally are first seen along edges of fields. The leaves turn a yellow red to reddish brown. The entire leaf blade may die prematurely. The plants generally are stunted and heads of infected plants often are severely blasted and seed is low in test weight. Control is accomplished by growing tolerant or resistant varieties. Early planting also is helpful in reducing damage caused by BYD. Refer to the latest variety selection guide to identify varieties with tolerance or resistance.
Smuts of oats have not been serious problems in western Canada but have reached epidemic levels in other areas of Canada and northern United States. As with loose smut of barley, this disease can be controlled with seed treatment. Refer to the most recent edition of provincial Crop Protection Guide for details of the registered seed treatments.
Fungal leaf spots
Helminthosporium and Septoria species cause fungal leaf spots on oats. These leaf spots are occasionally a problem in western Canada. They would be expected to be most serious where oats have been planted on oat stubble and if moist, rainy weather persists. These diseases can be controlled through rotation. A number of fungicides are registered for the control of leaf spots. Refer to the most recent edition of provincial Crop Protection Guide for details of the registered products.
Blast of oats occurs when the spikelets do not develop completely and sterility results. Virus diseases, such as barley yellow dwarf and oat blue dwarf, may cause blast. More frequently, blast is due to excessively high temperatures and moisture stresses occurring at the time of panicle differentiation and pollination.
Early planting reduces the likelihood of blast while late seeding and high seeding rates may favour the occurrence of blast.