Combatting Fusarium before it’s visibleA Fusarium Head Blight (FHB) survey of over 900 cereal and corn fields in Alberta in 2010 showed the disease is spreading beyond irrigated areas. Research indicates it is a disease well-worth fighting before you see it.
FHB, also called scab or tombstone, is caused by several species of the fungus Fusarium, of which the most significant is F. graminearum. Farmers in Manitoba, eastern Saskatchewan, and irrigated areas of Southern Alberta have to battle it every year.
“We’ve been most concerned about wheat, especially durum, because it’s the most affected by the fungus,” says Ron Howard, Alberta Agriculture plant pathologist. “But barley, corn, oats, rye, and grasses can also be attacked.”
Fusarium fungi can overwinter in the soil, on infected cereal and corn residues, and on seed. Overwintering fungal fruiting bodies on crop residues release spores in the spring and summer, which can spread to cereal and grass heads and corn ears when they are in flower. Spores that reach a cereal flower can infect the developing kernel. Infected heads may exhibit white or pinkish fungal growth that produces more infective spores. Spores are carried on air currents to other plants and adjacent fields.
Like most fungal diseases, Fusarium thrives in cool, moist weather, but it doesn’t need a lot of moisture—a shower is enough to spread the disease and create conditions that favour head infection. Soil-borne Fusarium inoculum can infect plants at different stages of growth and cause seedling blight and crown and root rot in cereals, as well as stalk and ear rot in corn.
FHB cuts yields of barley and other cereals, but the biggest loss is from mycotoxins produced by Fusarium species in affected grain. F. graminearum typically produces more mycotoxin than the other Fusarium species that cause FHB.The main toxin is deoxynivalenol (DON) and grain buyers specify a maximum level of DON for their purchases. Agriculture and Agri-Food Canada advises a maximum of one part per million DON for pigs, dairy cattle, and horses; and five parts per million for poultry, beef cattle, and sheep. Maltsters have zero tolerance for DON—it leads to beer that gushes when it’s opened.
“Even tiny amounts of F. graminearumin a malthouse are a serious issue,” says Pat Juskiw, barley breeder at the Lacombe Field Crop Development Centre. “The fungus can grow and produce DON on grain in the warm, humid environment of the malthouse.”
Fusarium graminearum management plan
Because FHB is so destructive and easily spread, Alberta designated F. graminearum as a “declared pest” under the Agricultural Pests Act in 1999 and has developed a set of best management practices to control it. These practices are described in the Alberta Fusarium graminearum Management Plan (www.agric.gov.ab.ca). Under the plan, all grain trucks must be securely covered and any cereal seed intended for planting—even bin run—must be accompanied by a laboratory certificate showing it has been tested and no detectable F. graminearum has been found. Cereal grains grown out-of-province and destined for use as seed in Alberta must be free of detectable F. graminearum as determined by a lab test, and also must be treated with a fungicide seed treatment effective against seed-borne Fusarium.
Survey resultsHoward has run FHB surveys across Alberta in the last two years. His cooperators, including agriculture service boards and applied research associations, sampled cereal and corn residues and grain heads, which he then had lab tested. A few other fungal diseases can look similar to FHB and produce “Fusarium-damaged kernels” (FDKs), so a lab test helps to determine the exact cause of these symptoms.
Not all of the Fusarium species associated with FHB or FDKs are capable of producing mycotoxins, but F. graminearum typically produces the most DON in infected seed.
“In 2010, we found F. graminearumin crop residues from 5.9 per cent of wheat, 13 per cent of durum, six per cent of barley, zero per cent of oats, and 42.2 per cent of the corn fields sampled,” says Howard.
Among the cereal grain samples collected in the provincial FHB survey, the proportion that tested positive for F. graminearum was: 13.5 per cent of wheat; 40 per cent of durum; 3.3 per cent of barley; and zero per cent of oats.
“Most of the FHB-infected fields were in irrigated areas of Southern Alberta, but samples from four cereal fields in Central Alberta also tested positive,” says Howard. “The infection level was extremely low, but it shows farmers need to be vigilant and follow the management guidelines.”
In 2011, Howard intensified sampling in counties that were missed in the 2010 survey, had low infection rates, or bordered areas of heavier infection. Lab testing of these samples should be completed soon.
So far, 20/20 Seed Labs has seen lower levels of F. graminearum in 2011 than in 2010—8.5 per cent of barley samples tested positive in 2011 compared to 14 per cent in 2010. Levels of infection are lower, too, averaging 2.1 to 5.5 per cent in 2011, compared to six to 30 per cent in 2010.
BioVision Seed Labs has seen similar trends. Terry McIntee, the company’s Edmonton lab manager, has seen a return to “normal” levels after very high levels in 2010.
“Fusarium graminearum is endemic in Manitoba,” he says. “About 90 per cent of seed lots from there tested positive for the disease in one to two per cent or more of seeds. Across the rest of the prairies, disease incidence was patchy in 2011.”
McIntee says that FHB follows weather patterns and is much more common in a wet year. He noted that, although FHB was comparatively higher in the areas of Saskatchewan that flooded, it was much lower in areas with good weather and no rain during cereal flowering.
“About 25 per cent of seed lots sent to us from Alberta and Saskatchewan have one or two per cent of Fusarium-infected seed,” says McIntee. “In the past, it’s usually been 10 to 20 per cent.”
McIntee pointed out that most of Alberta’s Fusarium-infected grain is from irrigated areas.
Howard advises farmers not to seed cereals into corn stubble or any fields affected by the disease the previous year.
“Fusarium is very common in corn, where it causes a stalk rot and occasionally ear rot, so we advise seeding non-cereal crops, for example peas or canola, into corn stubble to help break the disease cycle,” he says.
Planting Fusarium-resistant cereal varieties would be the best strategy against FHB; however, none of the currently registered varieties have strong resistance, although some are less susceptible than others. Consult Alberta’s Seed Guide at www.seed.ab.ca for information on the relative susceptibility of cereal varieties to FHB.
“Six-row barley varieties are generally more susceptible to the disease than two-row varieties,” says Howard.
Heavier seeding rates reduce tillering and shorten the time when flowers are open and susceptible to infection. Fungicide application at flowering protects against infection, but a second application may be needed if flowering is prolonged. Under irrigation, Howard advises filling the soil profile just before flowering to avoid watering during flowering to minimize infection risk.
If you see FHB in the field, you may be able to reduce the number of FDKs that could end up in the harvested grain by increasing fan speed to blow the lighter, damaged kernels out of the combine. Unfortunately, this has the drawback of increasing the inoculum in the field, potentially causing problems the following year.