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Clubroot — You Don’t Want It

DISEASE MANAGEMENT

While the clubroot disease in canola is still isolated to a relatively few counties in central Alberta, farmers across Western Canada are being warned to be vigilant in preventing the disease from appearing or worsening on their farm.

Clubroot is one of those flypaper diseases in that, once it appears, it is extremely difficult to get rid of, and if it takes hold and isn’t properly managed it can have devastating effects on production. If you’re not growing clubrootresistant canola varieties, and not following a recommended four-year canola rotation, the risk of a low disease level suddenly becoming severe is significantly increased.

“The disease can be found in varying levels in different parts of a field,” says Murray Hartman, provincial oilseed specialist with Alberta Agriculture.

“As the level of disease increases so does its effect on the crop, to the point at the higher disease levels producers can experience 100 per cent yield loss. And once it is there, it isn’t something you get rid of overnight or even over several years.”

Most Prairie farmers don’t have to be concerned that clubroot will suddenly appear in their canola crop this year. It is a soil-borne disease so unless you have machinery or trucks moving onto your farm that were previously in an infected field, the risk is relatively low. But all Prairie producers are urged to be cautious.

CURRENT STATUS

Clubroot is a disease that can affect canola, mustard and other crops in the cabbage family, including broccoli, cabbage and turnips. A leading theory on how it got established in these central Alberta fields suggests it was carried from a cabbage crop to adjacent farmland.

Hartman says the first clubroot infection was found in 2003 in a canola field near St. Albert, just west of Edmonton, and now has become a serious to moderately serious disease affecting hundreds of fields in 15 rural municipalities within a 125-kilometre radius of the original outbreak.

It has even been found in low levels in surveyed fields in two southern Alberta counties in the Brooks and Medicine Hat areas which are about 400 kilo-metres from original outbreak site. The clubroot population at these southern Alberta sites is notably different than around Edmonton, which suggests they had a different origin

BE WATCHFUL

While there have been no reports of clubroot in many rural municipalities across Alberta (see Alberta Agriculture’s website for a detailed map) and none has been found in the B.C. Peace River region, Manitoba and Saskatchewan, the fact it is out there means farmers should be alert to the risk.

“Even if you farm some distance from the infected area, it is worthwhile to investigate any suspicious patches in your canola crop,” says Hartman. “They are easy enough to spot when you are swathing the crop. They could be small patches were yield is way down, or the crop seemed to mature much earlier, but there are few plump pods with seed on the plants. Get off the swather and investigate.”

There could be any number of reasons for loss of production on these sites, he says. They could be infected by other diseases such as blackleg or sclerotinia, but pulling a few plants and examining the roots will quickly show if clubroot is the cause. Plants infected by clubroot will develop galls on the roots. The galls are actually nutrient sinks that tie up nutrients and prevent the transport of both water and nutrients to the above-ground plant parts, essentially starving the crop. Depending on disease severity the galls can be quite large, looking like a club.

“It is important to investigate these unproductive patches for different management reasons,” says Hartman. “But particularly to determine if clubroot is the cause.”

Even a shovel full of soil can hold billions of clubroot disease spores. The spores themselves cannot be transmitted from one site to another in the air, like sclerotinia or blackleg, but spores do attach themselves to soil and it’s the soil that is moved either by wind and water erosion or by transport on field machinery and vehicles that can spread the disease.

MANAGEMENT PRACTICES

Farmers in a high-risk clubroot area, or those who suspect a low level of the disease in a field, are urged to follow a few key management practices to prevent the disease from spreading and getting worse.

One fairly new tool is clubroot-resistant canola varieties. There are about a half dozen newer varieties registered with clubroot resistance.

“They are not a cure for the problem,” says Hartman. “But they help in reducing disease development, and many are very good, high yielding varieties, as well.” Several more varieties are in the development stage and should be available to producers in the next couple of years.

Another important management practice to reduce the risk of clubroot is to follow a proper four-year canola rotation. That’s a tough sell for many farmers, especially with current strong canola prices. Many are tempted to seed as many canola acres as possible and shorten rotation to as little as two years.

But because the disease can persist in the soil for many years, shorter rotations may mean short-term gain for long-term pain.

“Following a longer rotation doesn’t eliminate the disease,” says Hartman. “But it can slow it down. A shorter rotation can cause the disease to increase from a low level of infection to a high or severe level in a short period. With the longer rotation you may see disease levels reduced by about half between crop years, but if you have a billion spores in a soil sample to begin with that still leaves half a billion, so there is still a lot left for the disease to develop further. These spores

Infected plants develop galls on the roots, “clubbing” the end.

could remain viable in the soil for 15 to 20 years.”

Equipment sanitation is another key management tool to prevent disease spread. Farmers working in infected fields are urged to thoroughly clean and wash equipment before moving to other fields or off-farm. And producers hiring custom contractors need to ask questions and ensure any equipment being brought on the farm hasn’t come from the infected region or at least has been thoroughly cleaned.

This also applies to operators of utility or oil and gas service vehicles that may be moving into fields. Find out where they are coming from and ensure all vehicles have been properly washed.

Other important management practices, which help reduce disease spread include:

Using direct seeding and other conservation farming practices to minimize soil disturbance.

Avoiding the use of straw bales and manure from infested or suspicious areas. It is believed clubroot spores can survive through the digestive track of livestock.

Avoiding common untreated seed (including canola, cereal and pulse crop seeds). While the disease is not carried inside the seed, any soil on the seed could carry spores. Some seed treatment fungicides may be effective, but research is ongoing.

The risk of spreading clubroot by contaminated seed or straw is much less than by the transportation of contaminated field equipment.

ONGOING RESEARCH

Researcher are searching for better ways to manage clubroot, says Steven Strelkov, a professor and researcher at the University of Alberta at Edmonton.

Two key areas of research are identifying improved methods of disease resistance, and getting a better handle on how the disease spreads.

“New canola varieties with clubroot resistance are relatively effective against the most common pathotypes, or strains, of the disease,” says Strelkov. “And that presents a real risk. The more these varieties are used, the greater the risk of developing other pathotypes of the disease which are not resistant.

“So research is looking at other resistance mechanisms with resistance against other clubroot pathotypes. But, until that happens, it is important to use proper management practices, including a four-year canola rotation, to reduce the risk of developing resistant strains of clubroot.”

Researchers are also attempting to get a better handle on how the disease is spread. While it is known as a soil-borne disease, research is looking at how far spores can travel on wind and water-borne soil particles, and the survival rate of these spores.

LeeHartisafieldeditorforGrainewsatCalgary.Contacthimat403-592-1964orbyemailat [email protected]

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