There’s no “one best way” to manage fusarium. For best results, try an integrated management strategy that includes several steps
Fusarium head blight (FHB), also known as scab or tombstone, is a fungal disease that causes yield loss and grade loss. FHB can infect most cereal crops and some grasses, especially in areas that experience humid weather. The fusarium fungus is endemic in parts of Manitoba and Saskatchewan and given the right environmental conditions, disease will develop.
Weather patterns are the greatest factor in the development of FHB. The disease is most likely to develop when temperatures range from 25 C to 30 C and moisture is continuous for 48 to 60 hours when plants are in flower.
In areas where there is more risk of FHB development due to generally conducive weather patterns, or where farmers have had infection in previous seasons and may be worried that the pathogen has overwintered on crop residues, farmers will be looking for ways to control fusarium.
“It’s important to use more than one strategy,” says Jeannie Gilbert, a research scientist at the Cereal Research Centre in Winnipeg. “A careful choice of fungicide and optimal timing of application, along with a resistant variety and good crop rotation has shown that you can get incremental improvements in yield as well as lower DON (a mycotoxin associated with FHB) and lower FHB. By using all of these strategies you can hedge your bets and stand a better chance of getting a good crop in a year when there is disease around.”
While there is no magic bullet, here is a list of 10 management choices that can help control FHB.
Use two- to three-year crop rotations between cereals and grasses. Follow cereal crops with broad-leaved crops. A break of at least one year and preferably two years is advised between cereal, grass and corn production.
2. Variety selection
There are currently no resistant cultivars, but FHB may be more severe on semi-dwarf and durum wheat than on hard red spring wheat. Recently registered hard red spring wheat varieties that offer moderate resistance, the best available to date, include 5602HR, Waskada, Carberry and WR859 CL.
Barley is more resistant than wheat to FHB and oats are more resistant than either wheat or barley. Consult provincial seed guides for details of the resistance level of different cultivars to FHB and plant more resistant varieties, especially in high risk areas. Planting two or more varieties of wheat will spread out flowering times and reduce the risk of infection. Staggering planting dates within the recommended planting period will also vary flowering dates and may reduce the severity of disease.
3. Field preparation
Although the fusarium fungus overwinters on crop residues, trying to eliminate surface debris by tillage or burning will have little effect on disease prevention and can make soils more vulnerable to erosion. Even if completely eliminated from a field, spores can still be spread via wind from neighbouring fields or nearby grassy areas. Within a field, rain-splash can disperse spores to nearby plants. Controlling barnyard grass and quackgrass in fields and around field margins is important, as these are alternative hosts for the fungus.
Farmers should carry out tillage practices that would normally be used to manage stubble-borne diseases such as tan spot. Crop residue burning does not destroy the root and crown tissues, which are major overwintering sites for the fungus.
Do not seed wheat, barley or other small grain cereals into cereal or corn stubble. Corn stover is a major food source for the fungus and incidence and severity of FHB can be much higher in corn growing areas. Remember, the pathogen can overwinter in any cereal residue.
Use clean seed that is free from fusarium infection, or if a contaminated grain sample must be used, add a fungicide seed treatment to protect the seedlings from seedling blight. Seed treatments will improve germination of infected seed.
As most infections occur around flowering, and symptoms can develop within three days if environmental conditions are right, scouting should generally begin at this stage, especially if weather conditions are conducive, and continue for at least three weeks after.
Look for a pink or orange-coloured ring of spore-bearing structures called sporodochia at the base of the glumes. Partially-filled seeds will be found in infected spikelets and the shrivelled grains may appear tan to white, with traces of pink on the seeds.
In barley, FHB first appears as premature bleaching of spikelets, which contain shrivelled, chalky white seed. There may be an orange or black encrustation on the seed surface. Damaged wheat kernels may also be covered in a white to light pink mould. Fusarium-damaged kernels (FDK) in other cereals such as barley and oats can appear healthy, so the disease is much harder to identify.
Protection decisions being with assessing a crop’s potential value. “If your crop looks really good then it’s worth protecting,” says Gilbert. “If your crop is coming into flower and a rainy spell is forecast, be prepared to put the money into a single spray at flowering just to protect the crop.”
Fungicide applications can be used to control and suppress FHB but timing is crucial and will vary according to what product is used. Foliar applications of products likes Proline or Folicur in wheat should be made from when at least 75 per cent of the wheat heads on the main stem are fully emerged to when 50 per cent of the heads on the main stem are in flower, according to the manufacturer’s recommendations.
In barley, it is important to wait to apply until most of the barley heads have emerged, for maximum coverage and to protect the exposed florets from the risk of infection. Check provincial crop protection guides for a full listing of fungicides and their effectiveness against FHB.
Recent research from North Dakota State University recommends the following application guidelines for fungicides to achieve better suppression of FHB in small cereal grains.
Produce a fine- to medium-sized drop (300 to 350 microns) with an 80-degree flat-fan nozzle.
Angle all (flat-fan) nozzles forward 30 to 45 degrees down from horizontal. Thirty degrees is preferred over 45 degrees.
Apply fungicide at 10 gallons per acre for controlling FHB.
Position angled spray nozzles eight to 10 inches above the grain heads.
To reduce the number of fusarium damaged kernals (FDK) in harvested grain, combine louvre openings and air velocities can be adjusted to blow the lighter, diseased kernels over the back of the combine without losing too many good kernels. In fields which are severely affected by leaf diseases, the lower test weight of the grain may make it more difficult to separate normal kernels from FDK.
Fusarium damaged crops must be stored properly to prevent further mould and toxin development. Wheat infected with FHB that has a moisture content greater than 14 per cent should be dried using heated air to stop further disease development. Green feed should be drier than 20 per cent moisture. Grain drying or proper ensiling in an airtight silo will stop further mould development but will not remove the DON already present. Silage contaminated with FHB should be tested for DON levels prior to feeding.
9. Testing grain
Diseased heads can contain visibly affected kernels. FDK is the grading term given to visibly affected wheat seeds; in barley it is called fusarium mould. The Canadian Grain Commission (CGC) sets grading tolerances for fusarium-damaged wheat and barley.
The CGC and several companies across western Canada offer DON testing services for harvested grain and seed, and most have a minimum detection limit of 0.5 ppm. More accurate but costly tests can detect DON levels down to 0.05 ppm. It is important to send good, representative samples to the test laboratory to get accurate results. Ask your local agricultural representative for a list of companies in your area that offer testing.
Special care should be taken with feed grain and hay or straw that may potentially be infected with FHB to try and help avoid spread of the disease. The fungus in FHB-infected grain or hay is killed during passage through the digestive system of cattle, but it’s important to minimize and clean up any spillage. If infected grain comes into contact with the soil it could establish itself in fields or ditches. Try to avoid accidental contamination from spills during loading or unloading and cover trucks with a tarp when hauling feed grains. Store feed grains covered and clean harvesting, seeding and transportation equipment thoroughly.
Bedding straw represents a higher risk of spreading FHB because imported straw could have high levels of infection. If the straw is then spread on fields it can bring the pathogen in contact with the soil. Composting infected grain or crop residue (grass hay or straw) to reach a temperature of 60 C to 70 C for two weeks will kill any FHB present in the grain or crop residue. †