Fusarium head blight has been a stubborn threat to cereal crops in Western Canada since the 1990s. Some years are worse than others, but when the conditions favour this fungal pathogen, fusarium can cause significant losses in yield and crop quality in wheat, barley, oats and corn.
The two primary weapons against fusarium — fungicides and resistant varieties — don’t offer the same measure of control as they do for some other important cereal diseases. That’s why Kelly Turkington recommends an integrated approach incorporating best practices that can be used from seeding to post harvest to help farmers get a better grip on fusarium head blight.
Turkington, an Agriculture and Agri-Food Canada plant pathology researcher at Lacombe, Alta., discussed fusarium head blight management with Grainews about after delivering a presentation on the topic at the Manitoba Agronomists’ Conference in December.
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Resistant varieties
Turkington notes resistance to Fusarium graminearium, the main species found on Prairie farms, is generally improving, with breeders continuing to make incremental advances in reducing the incidence and severity of fusarium damaged kernels (FDK) and deoxynivalenol (DON) mycotoxins in infected crops.
However, he says growers still need to have realistic expectations around resistant varieties. Wheat rated MR for F. graminearum, for example, won’t provide the same level of control as a variety with an MR rating for stripe rust would, for example.
“Under favourable conditions, like we had in the eastern Prairie region this year, that MR rating reduces the amount of disease,” Turkington says. “You might have five parts per million of DON where you have a susceptible variety, but with your MR variety, you’re still looking at probably two to three parts per million of DON. It doesn’t eliminate it completely, so that’s something to keep in mind.”
Crop rotation
Fusarium can survive on the residue of infected plants, and in very short or continuous rotations of cereal crops, the pathogen can build up and cause serious infestations. Longer rotations of least two years between host crops allows more time for crop stubble to break down and therefore reduces the risk of fusarium infection.
Turkington notes many Prairie producers opt to grow a two-crop rotation, alternating between a cereal crop and canola, which is a non-host crop for fusarium. He says that isn’t ideal for limiting fusarium risk, but he recognizes disease control isn’t the only concern for farmers who have other important rotation considerations, such as commodity prices, reliable markets and management issues for non-host crops such as field peas.
“I always emphasize that I’m recommending a rotation based on my knowledge as a plant pathologist. But at the same time, I understand there are many factors that will influence what crops you decide to plant,” Turkington says.
“Long term, if we can get some better cropping options for growers, we may have a better suite of crops that growers can look at, providing that opportunity to extend the rotational interval between susceptible or host species.”
Turkington says in areas with farmland where F. graminearum is well established, longer rotations may not be enough to prevent a fusarium head blight outbreak in a field if the pathogen is a problem in another one close by.
He notes wind-blown fusarium spores can easily travel from one field to the next, which is why it’s recommended farmers to try to avoid planting small grain cereals right beside cereal or corn fields where F. graminearum levels are known or suspected to be high.
Seeding
Using good-quality certified seed, and seed that has been tested for the fusarium pathogen, is thought to be helpful in fighting fusarium head blight in cereals.
Turkington says for farmers in those parts of the Prairies where fusarium is already well established, the primary concern is how much F. graminearum is present in a seed lot and its likely effect on seed performance.
“It’s very important in that situation to have a seed test done to look at germination and perhaps vigour, and then, of course, the disease load on the seed. That will give you some clues as to whether there are some issues with that seed lot,” he says.
“You have to have pretty high levels of seed infection to start to see a significant drop in germination and ultimately field performance. Typically, once you start getting above about 10 per cent seed infection rate, that’s where a lot of these seed performance issues start to show up.”
Turkington said research has shown fungicidal seed treatments don’t provide complete control of seed to seedling transmission of F. graminearum, but they can give crops a better chance of withstanding the disease and establishing a more uniform stand.
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If pathogen levels aren’t too high in seed, he says, good-quality seed treatment that’s applied using good application technology can help ensure rapid uniform seed germination, resulting in uniform seedling emergence and growth and a uniform plant stand.
This in turn will lead to uniform head emergence within the crop and a more uniform target for fusarium fungicide applications during the growing season.
Turkington says farmers wishing to protect cereal crops from fusarium should be mindful of seeding rates as well.
“Seeding rates relate to the uniformity of the target you’re trying to hit with fungicide, which is the head tissue. Lower seeding rates will result in more secondary tiller development and a potentially wider window for potential infection to occur,” Turkington says, acknowledging that challenging weather or soil conditions at seeding may also result in variable emergence and non-uniform crop development.
“It makes it much more difficult to get good coverage of all the head tissue in that field (and) that may increase your risk in in terms of having some issues with fusarium head blight,” he says.
According to Turkington, limiting irrigation at certain times on irrigated fields can also help. Since fusarium head blight thrives in moist conditions he says, reducing or withholding irrigation water for as long as possible after head emergence can help reduce the risk of disease development.
Limiting residue
Because F. graminearum can overwinter in crop stubble, practices that facilitate decomposition of this residue will help remove a potential source of inoculum. This can include using combine straw choppers/spreaders or other implements after harvest to chop up crop residue and distribute it widely over the field.
Turkington notes the smaller residue pieces are, the faster they will decompose. He adds making sure there’s a good spread of material across a field will help prevent those thick swaths of chaff and straw that may contribute to fusarium buildup in subsequent years.
According to Turkington, adjusting equipment so that disease damaged kernels are blown out the back of combines during harvesting can be another effective control measure.
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U.S. research shows that by removing smaller, lighter weight fusarium-damaged kernels this way, it can lead to grade improvements and also reduce DON levels in infected grain, he says. The practice typically works better for wheat and durum than for barley and oats, because of the type and extent of kernel shrivelling that occurs in these crops.
A potential drawback of this approach is it may increase the fusarium risk to subsequent crops, since it means highly infected material is going back in the field.
Turkington says the decision then for farmers is whether the benefit they hope to gain by having a more marketable grain crop outweighs the disease risk from FDKs, which are very prolific producers of the wind-borne spore stage of F. graminearum.
Turkington notes weed seed destroyers mounted on the back of combines could be another useful tool for limiting the spread of fusarium inoculum since in addition to weed seeds they can crush FDKs.
“I look at the research my colleague Breanne Tidemann had done with harvest weed seed destruction technology and feel it has a potential role to play. Here, you’re basically pulverizing that FDK tissue and facilitating its more rapid decomposition in the field. So there’s a much more rapid disappearance of that as a source of the disease,” he says.
