Fusarium is the most devastating fungal disease of wheat in Canada, costing the industry over $1 billion annually in yield, quality and market losses in cereals, said Dilantha Fernando, professor in the Department of Plant Science at the University of Manitoba, in a presentation at the Crops Disease Summit held this past February in Sydney, Australia.
This revelation isn’t news for prairie farmers especially in Manitoba and Saskatchewan. They know first-hand the losses due to fusarium head blight (FHB), which is caused by the fungus, fusarium graminearum. Unfortunately, there is no way to completely eradicate FHB.
This is not to say the disease can’t be managed and losses reduced. But there is no single magic bullet — even the best fungicides on the market can only suppress the disease. Farmers must follow an integrated pest management program to have any hope of minimizing the damage.
To understand why this disease is so troublesome, consider the disease triangle. There are three factors that must be present for an outbreak: the pathogen, a host, and the right environmental conditions.
In the case of FHB, the causal pathogen is widespread across Manitoba, most of Saskatchewan and is rapidly expanding in Alberta. Spores survive for many years in the soil, on stubble, on seeds and even inside seeds. It can be spread by soil movement, water, wind, via seed or plant material.
Bruce Carriere, president of Discovery Seed Labs, told attendees at a Bayer meeting at Saskatoon in March: “Once you have it, it’s always there. You have to learn to live with it.”
Even if you’ve never had FHB in your fields, it can easily blow in from infected fields or grasses bordering your fields. And planting untreated seeds infected with fusarium is a sure way to bring the disease to your farm. Even treating infected seed is not 100 per cent effective in preventing disease transmission. This is why some areas of Alberta, still considered fusarium free, have a zero tolerance for using fusarium-infected seed.
It’s not just wheat, either. Most cereals and grasses, including barley, oat and corn, are susceptible to FHB. Spores can also survive on pea and canola stubble, which just adds to the problem. The key to breaking any plant disease cycle is rotation to non-host crops, and with so few options available to prairie farmers, there’s little opportunity to reduce FHB levels through crop rotation once the disease is present.
Finally, farmers have little control over environmental conditions conducive to FHB. Warm, wet conditions increase the prevalence of the disease. Temperatures between 25 C and » production and disease spread. While rain splash increases spore spread from plant to plant, high humidity or a damp crop canopy, for as little as 12 hours, is enough to increase spore development and release.
Of even more concern is the risk of a warming, wetter climate, which could increase FHB problems exponentially for prairie farmers.
So what can farmers do?
Farmers are advised to take a multi-pronged approach to FHB management. This has proven to be the more successful way to mitigate the effects of the disease. Below are several strategies to consider including in your FHB management plan.
Watch your seed source
First, if you are fortunate enough to not have FHB on your farm, under no circumstances should you plant infected seed.
Farmers in areas where FHB outbreaks have occurred in the past should not plant seed with more than five per cent fusarium graminearum infection, or 10 per cent total fusarium infection.
Carriere admits this may be hard to do this year given the low germination results he is seeing in the lab from last year’s crop samples, but stresses farmers need to stay away from seed with 15 to 20 per cent infection levels. By planting heavily infected seed, he says you are simply loading the levels of disease in the field.
If there is one bright spot regarding infected seed, Carriere notes that disease levels in seed carried over a full year (over a summer following the harvest of that seed) tend to drop by 50 per cent. So seed harvested in 2015 at eight or nine per cent infection may be in the range of four to five per cent infection in 2017. However, he warns there may also be a corresponding drop in germination that growers need to keep in mind.
Most importantly, seed treatments must be used if there is any detection of fusarium on seed. According to Carriere, “This is a rule!”
Increase seeding rates
Primary disease spread happens at flowering so if you can shorten the flowering period by reducing crop tillering, you reduce the risk of late infection.
Consider varietal differences Unfortunately all CWHWS, CWSWS, CWIW and durum varieties are susceptible to fusarium, so seeding these classes of wheat increases the risk of an outbreak. Some hard red varieties are rated as moderately resistant.
A couple of options for farmers wanting to grow wheat in high-risk areas include AAC Tenacious, a Canada prairie spring red with an R-rating for fusarium, or AC Emerson, a hard red winter variety also rated R.
Pay close attention to crop rotation
Rotate away from cereal crops for at least one year, preferably two. Do not rotate between cereals and corn, as both are susceptible to the disease. There is also an increased risk if you follow a two-year rotation of cereals and canola. Work done in Saskatchewan found this rotation actually increases the severity of fusarium infections over time.
Monitor your crop during the growing season
One way to check your crop for FHB is to cut the roots open and check for red vascular tissue. This is a good indication that the disease is present.
As well, track environmental conditions that are conducive to disease and spore development. Organizations such as the Saskatchewan Wheat
Development Commission have online fusarium risk maps based on real-time weather data. Use these maps along with cropping and disease history to determine whether or not you should spray a foliar fungicide.
Apply fungicides when necessary
When considering application of a foliar fungicide, you need to remember three things:
1. Fungicides provide suppression only, they will not provide total control.
2. By the time you observe disease symptoms it is too late to apply fungicides — they are not curative.
3. While the window is narrow there are still benefits in reducing FHB when spraying a little early or late but if you hit the optimal timing you do often get the best results. FF
A return on investment in foliar fungicides not only depends on timing of the spray operation but also on the application practice. If you are going to apply a fungicide, Tom Wolf, application specialist with AgriMetrix Research and Training, offers the following spray tips for FHB management:
1. Angle nozzles forward, or use double nozzles. 2. The greater the angle of the nozzle the better. 3. Use coarse sprays. 4. Maintain low boom heights. 5. Slow speeds are always recommended to ensure fungicides are applied correctly, especially if the spray needs to go deep into the canopy. However faster travel speeds are not as detrimental with FHB because the more horizontally the spray moves, the more droplets will stick to the heads. 6. Maintain over 10 to 20 gpa (45 to 90 litres) for fungicide applications.
FHB info for Saskatchewan farmers: www.farmforum.ca/FHBinfoforSK
FHB info for Alberta farmers: www.farmforum.ca/FHBinfoforAB
FHB info for Manitoba farmers: www.farmforum.ca/FHBinfoforMB