According to the 2013 producer harvest samples collected and analyzed by the Grain Research Lab (GRL) at the Canadian Grain Commission, 18 per cent of Canadian Western Red Spring wheat samples and 10.7 per cent of the Canadian Western Amber durum samples received from across Western Canada by mid-October were downgraded due to ergot.
According to GRL statistics, ergot incidence and damage has been increasing since 2010, with the most consistently high levels being seen in Alberta over the last few years. About two per cent of red spring wheat samples from Alberta were downgraded for ergot in 2009, increasing to 16.8 per cent in 2010, 27.8 per cent in 2011 and 15.5 per cent in 2012.
In Saskatchewan, ergot incidence on red spring wheat changed from seven per cent in 2009 to 4.8 per cent in 2010, 18.3 per cent in 2011 and 8.4 per cent in 2012. In Manitoba, 7.7 per cent of red spring wheat samples were downgraded for ergot in 2009, 8.1 per cent in 2010, 15.5 per cent in 2011 and 3.9 per cent in 2012.
“Ergot incidence appears to be trending higher in Alberta, but in Saskatchewan and Manitoba there is no clear-cut trend,” says Dr. Vikram Bisht, provincial plant pathologist with Manitoba Agriculture, Food and Rural Initiatives. “Whenever you see more rains you will have more issues; it’s just a matter of timing. This was reflected by higher downgrades in 2011. Hot and dry June and July in 2012 could be responsible for lower ergot in 2012 in Manitoba.”
Ergot is a fungal disease. Incidence is highly dependent on wet weather conditions during the two stages of the disease cycle — early spring and at the flowering stage. Rye is the most susceptible to ergot, followed by triticale, wheat and barley. Prolonged wet soils in spring and early summer promote germination of ergot bodies, which have usually over-wintered in the soil from previously harvested crops or in grasses along field edges. They they can also be introduced by infected seed. Ergot bodies (sclerotia) rarely survive more than one year in the soil.
The germinating sclerotia produce tiny mushroom-like structures called apothecia, which produce infective ascospores that become wind-borne. When these spores land on the plant florets they penetrate the ovaries of early flowering plants such as wild grasses, fall-sown cereals, or early-sown spring crops. Within five days of the floret being infected, the second stage in the disease cycle occurs, which is known as the “honeydew stage.”
If wet, cloudy and cool weather extends the period of flowering, it will increase the window of infection for the spores to enter the florets. “This year we had frequent rains during the brief period when nights were cool and this extends the period of flowering,” says Bisht. “When the period of flowering is extended you have honeydew on the grasses and the rains and wind carry the spores to new areas, new fields; and that is how it spreads.”
These weather conditions can also increase populations of insects such as aphids, thrips, midge and leaf hoppers, which are attracted to the sticky, sweet exudates during the honeydew stage and can help spread the infection. Once the ovary of a developing seed is infected it enlarges and is replaced with a hard ergot body.
Poor fertility and copper deficiency have also been linked to incidences of ergot infection. Both can cause delayed flowering which can cause the floret to remain open longer and be exposed to infection longer.
Ergot infection alone does not usually lead to significant yield loss, but can result in the grain being downgraded or in severe cases, rejected at the elevator. There is a low tolerance for ergot in cereals because the chemicals (mycotoxins) it produces are highly toxic to animals and humans and are not removed by processing.
A potential reason for the increase in prevalence and severity of ergot, say plant pathologists, may be shorter crop rotations. A typical rotation has become canola-cereal-canola-cereal. A one-year break away from cereals may not be sufficient to allow for the natural destruction of ergot bodies in or on the soil. Tighter rotations may also have increased the levels of ergot bodies in grassy areas adjacent to cereal fields.
Abundant rainfall over the past few years has promoted the growth of volunteer cereals and seeded grasses in fields and headlands which may also have enhanced the production of resting bodies and inoculum.
No cereal varieties are truly resistant to ergot and research has shown little difference in susceptibility across varieties or classes. Many growers will talk about Harvest being a particularly susceptible variety, but says Dr. James Menzies, phytopathologist with Agriculture and Agri-Food Canada’s Cereals Research Centre in Winnipeg, the fact that ergot seems to occur more often in this variety is probably more due to the fact that Harvest is a dominant variety grown on many acres.
“Ergot incidence is sporadic and because of the number of acres of Harvest grown it will definitely hit Harvest in many places,” says Menzies. “So people think that Harvest is most susceptible. Researchers feel this may not be true because without some replicated trials it is impossible to say that one variety is more susceptible than another.”
In U.S. research, where different wheat varieties were inoculated with ergot, every one of them got the disease. “That indicates that there is no real resistance,” says Menzies. “Escaping the disease is therefore one of the best ways growers can try to manage this problem.”
With no ergot resistant varieties yet available and no fungicide treatments currently registered for the disease, prevention is the best defence and crop rotation is probably the best management tool available to producers at present. “If a producer is growing an ergot-susceptible cereal one year, next year he should maybe grow a pulse or oilseed or something to break the disease cycle,” says Bisht. “The length of the crop rotation should be at least two years to break the cycle. If you have wheat and canola and then you plant something else and then have wheat, then I think you’re breaking the cycle very well, even though you are not taking care of all the inoculum that may be present, but most of them will have lost their viability within two years.”
It’s also a good idea to avoid planting spring cereals next to winter cereals to avoid creating a green bridge for the disease. Winter wheat affected by viral diseases can prompt management decisions that favour spread of the disease. “Under normal circumstances when farmers have planted winter wheat in the fall, they will not plant another crop in that field that year,” says Bisht. “The following year they will plant something like canola. But sometimes winter wheat has to be cultivated under because it develops wheat streak mosaic virus. Because the producer had canola last year, he needs to have another wheat crop, so he will plant spring wheat in that field. When he does this the ergot bodies can infect the new spring wheat crop very easily.”
Because grasses around field margins, in headlands or along roadways can provide a host for the ergot bodies, mowing then before they flower will help reduce the first stage of infection in the spring.
No seed treatments are effective against ergot, so it’s advisable to use clean, certified seed to prevent the disease from spreading to clean fields. In seed that is two years old the viability of ergot sclerotia may be reduced but even those that cannot germinate are still toxic and should not be used as feed.
It is possible to reduce the potential for ergot at harvesting time. Ergot levels are typically higher around the edge of the field, as this is where the spores come in from roadside grasses, and where insects are most active. “Usually the disease is coming in from the edges of the field,” says Bisht. “If a few metres of the field edge is harvested first and kept separate from the main crop then the chances of downgrading the whole field will be lesser.”
If significant levels of ergot are observed in the crop, farmers can delay swathing or straight cutting the crop. Ergot bodies become very loosely attached to the cereal heads and windy conditions that result in movement of the crop can shake the ergot bodies to the ground.
Seeding at higher rates can also be beneficial. “When you plant at a higher seeding rate you are reducing tillering and compacting the duration of flowering and because of that the main head gets infected, but no more new heads coming later will be affected by the honeydew stage,” says Bisht. “The secondary spread will thereby be reduced because you’re not extending flowering.” If a farmer knows there is likely some ergot in the seed, increasing the seeding depth may prevent the ergot bodies from reaching the surface and germinating, adds Bisht.
Good germination and use of a balanced fertilizer program so that the cereal crop is uniform in development will help plants avoid infection. Copper can be added to help control ergot, but will only be effective if soils are deficient in copper. Farmers can also try to plant all their cereal crops at the same time, so they flower over a narrower time period, which will help prevent the spread of the disease from one field to another.
Infected grain can be cleaned out as ergot bodies tend to be large and easily cleaned from the seed lot, but the process, which is often done with a gravity table or colour sorter, can be expensive and the producer will have to decide if the potential downgrade at the elevator makes it economically worthwhile to clean a particular lot of grain or seed.
Help may be on the way
There has been little research into ergot, but wheat and barley breeders are looking for varieties with some resistance.
A durum line, “9260B-173A,” was observed to have very good resistance to ergot. Studies are underway to characterize the genetic basis of this resistance and find molecular markers for use in plant breeding programs. This line is also being used in the durum breeding program of Dr. Singh at the Semiarid Prairie Agricultural Research Centre, AAFC, in Swift Current, Sask.
Another wheat line, “Kenya Farmer,” is also being studied to characterize its resistance to ergot. It’s been used in crosses by Dr. Fox in the CWRS wheat breeding program at AAFC’s Cereal Research Centre in Winnipeg, Man. It is hoped that, in time, some amber durum and red spring varieties with good resistance to ergot will be commercialized for production.
“A number of people are working to develop some ergot resistant lines, but I don’t know if any are near registration trials at this point,” says Menzies. “I hope that in the near future we will have some lines registered that have some resistance to this pathogen, but this is hard to predict. Lines must have more positive attributes than just ergot resistance. If the breeder develops an ergot resistant line but has very low yield, it is unlikely to be commercialized or make much of an impact on the prairies.”