Wet weather likely cause of surge in clubroot cases

A plant disease that was largely unheard of 10 years ago is emerging as a major threat to Alberta’s $2 billion canola industry.

A plant disease that was largely unheard of 10 years ago is emerging as a major threat to Alberta’s $2 billion canola industry.

Ron Howard, a plant pathology research scientist with Alberta Agriculture and Rural Development, described on Wednesday the rapid spread of clubroot and strategies to control it. He was speaking at the Agronomy Update 2012 conference in Red Deer.

“It is a significant threat to our canola industry,” said Howard, pointing out that badly infested fields may not even be worth harvesting.

Since it was first discovered in canola fields northwest of Edmonton in Sturgeon County in 2003, clubroot has spread quickly. As of last year, 830 infected fields had been found in Alberta, including one detected this fall in Red Deer County.

“The number of new cases in 2011 represents the biggest single-year increase in clubroot-confirmed fields in Alberta since the 2003 surveys were started,” said Howard.

Last year’s wet weather likely contributed to the jump, he said.

“If we get favourable weather conditions, we might even crack the thousand-field mark this year.”

The high precipitation levels in Central Alberta make this area particularly vulnerable, Howard said.

Despite being a relatively new threat in Alberta, clubroot has a long history in Europe.

“It’s been known as a vegetable disease, actually back to the Roman times.”

In addition to canola, clubroot attacks other cruciferous crops and weeds, including mustard, cabbage, broccoli and cauliflower. Its name was derived from the galls that form on the roots of infected plants.

Clubroot spores can remain dormant for years, with a Swedish study concluding that they can survive for up to two decades, said Howard.

“This is a very difficult disease to manage once it gets into a field, because of those long-lived resting spores and the fact it has a broad host range that includes volunteer canola and many of the cruciferous weeds.”

Clubroot can easily spread from field to field, often by way of infected plant material and soil that sticks to farm machinery and other equipment. These should be scraped, pressure-washed and disinfected when moving from an infected field, said Howard.

Other management strategies include extending the rotation period between canola crops, using clubroot-resistant seed, employing direct-seeding and minimum-till farming practices, avoiding untreated seed from infested crops and scouting fields regularly.

Howard also cautioned against spreading straw, greenfeed and other materials from infected fields onto clean land. This even applies to manure, he said, because clubroot spores can survive livestock digestion.

Clubroot-resistant canola hybrids are susceptible to the disease, he said, but cases tend not to be as severe.

“You can still see small galls on the roots in up to 10 per cent of the plants in some of those fields.”

Howard expressed concern about short crop rotations exacerbating the problem.

“This rapid build-up of inoculum that’s going to happen with shorter rotations in the clubroot-infested areas is going to mean that we’re probably going to see more economic damage from the disease, and also the possibility of the beginning of the erosion of resistance in our resistant varieties.”

The battle against clubroot received a boost in 2009, when Agriculture and Agri-Food Canada launched the Clubroot Risk Mitigation Initiative, said Howard.

“About $4 million has gone into clubroot research from this program over the past four years.

“There are about 50 scientists and technicians working full- or part-time on clubroot here in Western Canada now, making us a world centre for clubroot research.”