While there is no so-called cure for fusarium head blight a whole series of proper agronomic practices can be applied to stave off the impact of the disease, say Agriculture and Agri-Food Canada researchers.
Using FHB-resistant cereal varieties and applying registered fungicides is part of the story say Kelly Turkington, plant pathology researcher in Lacombe, Alta., and Brian Beres, agronomy researcher in Lethbridge, but it is a combination of proper practices from seeding right through to residue management at harvest that collectively provide the biggest bang for disease prevention efforts.
And, they point out, there is only so much proper cultural practices can do. If there is a heavy disease load in the soil, the crop is growing, and it’s a wet year with environmental conditions conducive to disease development, crops can be nailed hard.
Fusarium head blight, Fusarium graminearum species in particular, has demonstrated an ebb and flow of severity across Canada, as the disease has crept its way across Western Canada mostly since the mid-1990s. While the disease has established itself in varying degrees in all Prairie provinces, much of its annual impact on susceptible crops such as wheat, barley, oats and corn depends on growing season conditions.
Disease levels and damage to crop quality reached record highs during a relatively wet 2016 growing season, while disease levels were considerably lower during the dryer 2017 and 2018 growing seasons.
“That doesn’t mean it goes away,” says Beres. “In a dry cycle the disease may appear to be less problematic, but if growing conditions are favourable it can be back with a vengeance.” He says even on farms with extended rotations or using chemfallow years, once the pathogen is present it will find somewhere to colonize during a dryer year and seemingly explode into a crop if wet or high humidity conditions prevail.
Turkington says once the disease establishes itself in crop residue it will persist. “The disease pressure can drop depending on growing conditions,” he says. “But if high humidity develops in the crop canopy the disease can flare up. It may not affect the seed head of the crop, but it can infect the vegetative part of the plant and colonize there. Even with a four-year rotation on one farm the pathogen level could be greatly reduced, but what is happening on neighbouring fields?”
The researchers suggest a “systems approach” to minimize the presence and effect of FHB, and recommend the following steps:
1. Resistant varieties: Select and grow varieties with highest FHB-resistance rating available. There are several red spring wheats rated Moderately Resistant (MR), and a few CPSR and CWSP classes also with the MR rating. AAC Tenacious is a CPSR variety with a Resistant (R) rating. Among winter wheats, Emerson is rated Resistant. Among the durums, Intermediate is the highest rating. Beres notes the resistance rating is an indicator, but if the disease pressure is high it likely won’t stop it.
2. Good seed: Start with good quality certified seed, or at least seed that has been tested FHB-free.
3. Seed treatment: Use a good quality seed treatment to help get crops growing vigorously.
4. Seeding details: Once you have good quality, disease-free, treated seed in hand, there are several important points to consider: seed early, seed at a high seeding rate and use some starter phosphorus in the seed row.
5. Seeding rate: Beres recommends a seeding rate of 450 seeds per square metre (45 seeds per square foot) for winter wheat, which after expected mortality, should produce 30 to 35 plants per square foot. He adds that durum and CWRS varieties also perform well at 450 and therefore recommends at least 400 seeds per square foot for most spring cereals other than malt barley, which requires a rate of 300 to 350 seeds per square meter. This gets more main stems of the crop in the field with reduced tillering for greater uniformity.
6. Seeding early: Research is also showing that very early seeding — when the top five centimeters of soil is about 2 C — gets the crop off to an early start, may influence the crop’s flowering duration and disrupt the disease’s ability to survive.
7. Fertilization: Proper fertility — starter P in the seed row — helps to get the crop off to a good start which helps benefit uniformity, and also ensures the crop has enough nutrients to achieve the target yield.
8. Uniform crop: robust, even-maturing crop stand contributes to more effective use of fungicide. With more main stem seed heads flowering the fungicide is reaching more of the target. If 25 to 30 per cent of the stand is tillers that are still in the boot stage, for example, the fungicide is only reaching 70 to 75 per cent of the crop when it can be most effective.
9. Calibrated sprayer: Along with the above, it is important to make sure the field sprayer is working properly and properly calibrated to deliver the fungicide as evenly as possible.
10. Limiting residue: At harvest, a few different approaches can be used to avoid leaving a heavy layer of crop residue sitting on the soil to serve as place for the disease to colonize. Finely chopping and widely spreading residue is one approach. It may also be a benefit to collect straw and chaff and remove it from the field.
11. Don’t turn to tillage: What might be considered as conventional tillage in Western Canada has been found not particularly effective in controlling FHB. So don’t turn to tillage. Some research is showing that moldboard plowing to bury crop residue might help to reduce disease load, but that is an extreme measure with other consequences that don’t fit conservation farming practices.