There are four diseases of oat that typically affect the crop each season. The two major ones, stem rust and crown rust, sweep into Manitoba and eastern Saskatchewan each year when the weather is favourable.
Moisture and temperature are the drivers of disease and when established in a field, the pathogen will spread from plant to plant.
Breeding for resistance to these diseases is time consuming and costly. Furthermore, sources of new plant resistance, the means by which the oat plants defend themselves, are more difficult to find and incorporate into breeding programs. In any crop, there is a finite source of resistance genes. The crown rust fungus for instance continues to evolve and develop new races that are able to overcome genetic resistance. Therefore, resistant varieties become susceptible to crown rust as new races develop.
Some diseases are regionally specific Know what diseases are common in your area.
Crown rust (Puccinia coronata)
Crown rust, sometime called “leaf rust”, generally is the most widespread and destructive disease of oat in western Canada. Crown rust can reduce yields, lower test weights and groat percentage, and increase lodging through a weakening of the stem.
“Annual yield losses resulting from crown rust in the eastern prairie region (Manitoba and eastern Saskatchewan) were reported to average 5% during 2001 to 2005” (Menzies et al. 2019).
Crown rust is identified by the pustules on the leaf producing yellow-orange spores that infect leaves primarily (Figure 4.3). As the crop approaches maturity, a black spore stage (teliospores or “resting spores”) may also be found on the oat leaves, appearing as a black or dark brown ring around the yellow-orange pustules.
These black spores are the overwintering stage, although in western Canada they generally do not survive the cold. The name “crown rust” comes from the microscopic look of those teliospores which have a crown like structure on their surface.
Each spring in Canada, spores of this fungus and stem rust are blown in from winter, oat-producing regions in the southern United States (Figure 4.4).
The Red River Valley in Manitoba is the first area to receive the spores from the south, (Figure 4.5) and the crown rust infections will gradually spread to the western Prairie depending on weather conditions.
“Ideal conditions for oat crown rust are mild to warm daytime temperatures, so sunny days at about 20 C to 25 C, and moderate nighttime temperatures around 15 C to 20 C, along with good dews and adequate moisture.” – Albert Tenuta, plant pathologist, Ontario Ministry of Agriculture, Food and Rural Affairs.
Management of crown rust
More than 500 distinct races of Puccinia coronata have been identified. The highly variable race structure creates a challenge to breed oat lines with effective and stabl resistance. However, growing varieties with disease resistance is an effective and economical method of controlling crown rust. 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 greater. Crown rust may also be controlled using fungicides (Figure 4.12). Refer to the most recent edition of provincial Crop Protection Guide for details of the registered fungicides with which crown rust can be controlled.
Stem rust (Puccinia graminis f. sp. avenae)
Stem rust epidemics are infrequent on the Canadian prairies, but they have the potential of being serious in southern Manitoba if the oat crop is planted late and winds blow spores in from the south. Spores of the fungal pathogen stem rust, like those of crown rust, drift northward seasonally from the U.S. in a weather dependent manner.
Stem rust and crown rust are distinguished fairly easily on the basis of spore color (Figure 4.6).
The coloured and dusty pustules erupt on the plants and release hundreds of thousands of spores to the air which may infect neighbouring plants and produce new pustules within 7 to 10 days. These colourful mid-summer spore types are replaced in August with a mass of black overwintering teliospores. As mentioned earlier, winter temperatures in western Canada are too cold generally for the spores to survive.
Management of stem rust
Control of stem rust, as with crown rust, can be 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 for crown rust resistance. Stem rust resistance at first however, was more difficult to breed into the oat crop.
Stem rust may also be controlled using fungicides (Figure 4.12). Refer to the most recent edition of your provincial Crop Protection Guide for details of the registered fungicides with for controlling stem rust.
Barley yellow dwarf virus
Barley yellow dwarf (BYDV) is a virus that can cause significant yield loss in oat 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 (Figure 4.7).
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. Additionally, aphids can overwinter in winter wheat or grasses of field edges that form a green bridge for the aphids.
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 (Figure 4.8). The plants generally are stunted and heads of infected plants often are severely blasted and seed is low in test weight.
Barley yellow dwarf management
Oat varieties have some tolerance but there are no resistant varieties to BYDV. Early planting can be helpful in reducing damage caused by BYDV.
Loose smut (Ustilago avenae) and covered smut (Ustilago kolleri)
Smuts of oat have not been serious problems in western Canada (Figure 4.9). As with loose smut in barley, this disease can be controlled with seed treatment.
Most oat varieties are resistant to smut and provide good control of this fungal disease. Consult crop protection guide for details of the registered seed treatments.
Fungal leaf spots
Leaf spots on oat can be caused by a fungal pathogen known as Septoria avenae blotch.
The disease is prevalent in eastern Canada but is of minor importance in western Canada. A crop rotation which puts two years or so between oat crops will help reduce the carryover of this disease organism. Several fungicides are registered for the control of leaf spots (Figure 4.10).
Refer to the most recent edition of your provincial Crop Protection Guide for details of the registered products.
Florets are the developing flower structure on an oat panicle which typically forms two seeds. Oat blast occurs when the florets do not develop completely and sterility results (Figure 4.11). When blast is observed, the florets are seen as white, skinny and empty.
Frequently, blast is due to high temperatures and moisture stress occurring at the time of panicle differentiation. As blast is a stress related condition in oat, diseases may contribute to the problem. Early planting reduces the likelihood of blast while late seeding and high seeding rates may favour the occurrence of blast.
Fusarium head blight (FHB) is a fungal disease that is known to affect oat as well as other cereals (Bailey et al. 2003). Compared to wheat and barley, oat is less affected by the disease and may be more resistant. The causal agent can be one or a complex of several Fusarium species. In wheat, Fusarium graminearum was most prevalent while in barley F. graminearum and F. poae was prevalent. In oat, F. poae was most prevalent. Yield losses may be in the form of poor seed fill, floret sterility or impaired seed germination (Bailey et al. 2003). FHB is difficult to detect in standing oat crops. The major concern is the presence of mycotoxins on harvested seeds (Tekauz et al. 2004).
Deoxynivalenol or DON is the most common mycotoxin and is a risk to human and animal health, and can result in a lower grading for oat. FHB is of highest concern in Manitoba and Saskatchewan with limited economic importance in Alberta (Tekauz et al. 2008). This disease is most common in the black soil zone, associated with high rainfall. The spread of disease is assisted by rainfall during crop flowering but can also occur via wind and planting of infected seed (Canadian Grain Commission, 2010).
Chemical control of diseases of oat
The decision to grow a disease resistant variety is a tool for a successful growing season on the farm. Fungicides are also an important tool for the protection of a significant investment during the crop production season. Many growers choose to apply a fungicide even on a variety that shows good disease resistance. The two can work together for success, and starting with a disease resistant variety is like a backup plan (see Research Report below). Should the weather be such that getting to the field to spray a fungicide is not possible, the oat crop with its disease resistance, will provide a good safeguard for your investment.
A number of fungicides are registered for use on oat. Many growers consider applying fungicide when the yield potential and value of the crop is high, when leaf diseases in the area develop early in the season and also if the long-range weather forecast is for continued moist weather (see research report below). Refer to the most recent edition of your provincial Crop Protection Guide for details of the registered products.
- Alberta Guide to Crop Protection (2020)
- Saskatchewan Guide to Crop Protection (2020)
- Manitoba Guide to Crop Protection (2019)
Research Paper (2014): Canadian Journal of Plant Science (2014) 94: 911-922
“Are fungicide applications to control crown rust of oat beneficial?”
W.E. May, N. Ames, R.B. Irvine H.R. Kutcher, G.P. Lafond, and S.J. Shirtliffe.
Crown rust causes significant damage to the Canadian oat crop and the organism continues to evolve. Plant breeding efforts continue to develop varieties that defend the crop against the disease. “Currently, prophylactic fungicide applications are recommended to oat growers by industry agronomists, even in the absence of symptoms. Our objectives were to determine the influence of seeding date, cultivar and fungicide application on oat yield and quality in Saskatchewan and Manitoba.”
In this study, conducted from 2009 to 2011, 6 locations were chosen: two in Manitoba and four in Saskatchewan. The locations were: Portage la Prairie, Brandon, Indian Head, Canora, Melfort, and Saskatoon.
AC Morgan, CDC Orrin, CDC Boyer, and Leggett were the varieties tested. With respect to crown rust resistance, they are categorized as very susceptible, susceptible, partially resistant and resistant, respectively.
One fungicide was used in the study, the pyraclostrobin compound Headline®.
“These results indicate that prophylactic fungicide applications are unlikely to provide yield improvement when early planting is combined with even a moderately disease-resistant cultivar.”
“The only cultivar that consistently benefited from fungicide application was AC Morgan. Seeding in mid-May with even a moderately crown rust susceptible cultivar eliminated any benefit from fungicide application. In conclusion, it is recommended that growers seed early with a crown-rust resistant cultivar to avoid the need to apply a fungicide on their oat crops.”
Oat are not targeted by a great number of insects. Insects such as cutworms, wireworms and grasshoppers can all cause damage to oat. Aphids may also affect oat more so as a vector for Barley Yellow Dwarf Virus than any actual impact on yield or quality.
Refer to the most recent edition of your provincial crop protection guide (links above) for details of the registered products for specific insect control.