Oat growers across the Prairies have a number of foliar diseases to watch out for in their fields: crown and stem rust and septoria leaf complexes. Oats can also harbour a lot of different species of fusarium but, to date, fusarium hasn’t become an issue to the point where it has impacted oat yield or quality.
Disease management strategies begin with choosing the right varieties, says agronomist Jason Voogt, with Field 2 Field Agronomy in Carman, Man. Producers need to be aware of which resistant gene packages different varieties have, while researchers and agronomists are keeping a close eye on the length of time they’ll have diseases overcome some of those resistance packages.
“We know that because of the nature of crown rust, that it can develop resistance to the resistant genes that we currently have in plants,” says Voogt. “We’re also aware of the need to change things up as far as varieties if necessary, but disease management always a start with the variety and also looking at the rotation.”
It’s important to understand the difference between fungal, bacterial and viral diseases, how they occur and how to manage them. Producers can find some good information about oat diseases on the Prairie Oat Growers Association (POGA) website.
Fungal diseases include things like crown rust, stem rust, septoria leaf blotch and fusarium. Producers have options including early seeding (for rusts that arrive in spring), resistant varieties (in the case of crown rust only) and fungicides to manage fungal diseases in oats.
Fungicides are not effective against diseases caused by bacteria, such as bacterial blight, so the best option for management is good crop rotation.
Viral diseases like barley yellow dwarf virus, although not as common as other oat diseases, cannot be controlled by chemicals, and while some oat varieties are more tolerant of the disease, none are resistant to it. Early seeding and plant rotation can be effective management techniques.
Crown and stem rust
Because rust disease spores blow in on wind currents from the United States, agronomists and provincial disease specialists keep a close eye on the movements of rust up through North Dakota to Manitoba, Saskatchewan and Alberta to try and determine the potential each year for rust to occur. “Combine that with our current, local weather conditions and then from there we will determine if a fungicide application is necessary,” says Voogt.
Most provincial agriculture departments issue crop disease and pest updates throughout the growing season, and another good source of information for growers, especially in regards to these types of wind-blown foliar diseases, is the North Dakota State University Crop and Pest Report, which producers can subscribe to free of charge online.
“NDSU puts that out every Thursday during the growing season, and if crown rust is an issue there, they’ll talk about where it is, what severity as far as what counties they’re finding it in and they track it,” says Voogt. “Being able to see the progression maybe northward it can indicate when we might have to start doing tighter scouting, and if it’s going to be coinciding at all with the susceptibility of the varieties that we’re growing, because the disease may come in late enough that we’re already past the time of susceptibility.”
Scout to make sure it’s rust
In oats, the crop is most susceptible to crown rust at the early flag leaf stage through to panicle emergence, so that’s when producers should be scouting diligently if there is a risk that the pathogen may be present. As well, whenever the leaf remains wet for 12 or more hours, so when heavy dew, rain or thunderstorm events have taken place, spores that drop out of the atmosphere into the crop have a very suitable environment for infection.
“Those are the kind of things producers want to be watching for in that particular window of susceptibility,’ says Voogt. “On top of that, when they are out there scouting, they need to check not just the upper leaves but the lower leaves of the plants for the early stage of what might be crown rust.”
Typically, producers will see a very small chlorotic area on the leaf that eventually forms a bright orange pustule. Because other diseases, like bacterial blight, can look similar to crown rust though, Voogt says producers should rub the pustule with their thumb or finger nail to see if the rust comes off.
“At that timing stage, bacterial blight is another disease we should keep an eye out for,” says Voogt. “In some cases, some of the lesions will look quite bright in colour and sometimes can be confusing to a grower as far as comparing it to crown rust, so that physical wiping of that rust pustule to see it comes off is probably the truest way to find out that it is truly rust and not something else that look alike.”
Stem rust tends to arrive a little later than crown rust, but there are no resistant varieties for producers to choose, so it’s something that needs to be watched for. Last year’s dry seeding conditions meant some oat crops emerged unevenly, and later in the season, Voogt noticed later emerging plants in wheel tracks and drains that retained more late moisture, did have some stem rust.
“It came in late enough that it wasn’t a concern, but it is something that we want to continue to watch out for because if it ever arrives earlier, it would be something that we’d have to be looking at dealing with a possible fungicide application,” says Voogt.
Rotation an essential tool
Bacterial blight is caused by a bacteria and so fungicides are not effective against the disease, which has the ability to overwinter on straw or seed, so good straw management that allows straw to decompose, proper rotation and using clean seed are all effective control methods.
Rotation remains an important tool for disease management in oats. “I would suggest every two to three years, more likely three, would be probably the best-case scenario for a grower to be looking at rotating out of oats for disease management, especially for those diseases that do overwinter, like the bacterial blights and maybe to the lesser degree septoria species to allow that straw to decompose properly,” says Voogt. “If we are starting to see those diseases becoming more common then I think that’s probably where a grower would have to maybe look at widening that rotation even more.”
Septoria leaf diseases are similar to the other diseases in that they thrive under moderate temperatures and moist conditions where there is 12 or more hours of leaf wetness, but they generally occur earlier in the growing season because they primarily come from infected straw.
“It is not a primary concern because usually we haven’t had oats on those fields for a number of years so there isn’t going to be a lot of those cases where a local infection come in from straw unless for example, a field is that’s adjacent to a field that was oats the previous year,” says Voogt. “You could then see the movement of disease from rain splash and things like that into the adjacent crop, but if we continued to have leaf wetness early in the growing season, you would probably see a little bit more development if that straw is there to produce the spores.”
Besides using crop rotation, the same fungicides registered for managing crown rust or stem rust are registered on septoria, and application at early flag leaf is the most effective to give protection at that stage and at panicle emergence as well.
Watch for look-a-likes
As well there can be damage to plants that looks like a disease but is in fact caused by environmental conditions, with the hot, dry conditions this past summer being a good example.
“It doesn’t happen every year, but we had it happen this past summer where we had rapid growth of the crop followed by very hot, humid days with strong winds,” says Voogt. “A few days after we started to notice the oat crops had a very dark, almost brownish hue to them. The newly emerged leaves looked like they were burnt off and that was due to those winds. So basically, it was rapid growth, susceptible stage of the crop combined with this hot wind where you were losing lots of moisture out of the leaves and quicker than it could replenish them and so you were getting this leaf tip scorching.”
Something like this, which can develop in a short period of time can cause a lot of panic, so Voogt had to get the message out quickly to growers that this was an environmental issue and not a disease. “We didn’t want them to start applying a fungicide because it wouldn’t do anything, and the oats would recover and there would not be a yield impact.”
With both crown rust and stem rust, the primary source of infection is going to be re-infection coming up from North Dakota and further south in the U.S., but there is an alternate host in Manitoba for crown rust, which is a shrub that grows along certain creeks and tributaries called buckthorn. “There is a potential for infection coming from there within Manitoba in the growing season, so producers growing oats close to areas where buckthorn is present could tighten up their scouting just to be aware of it,” says Voogt.