LANGDON, N.D. – Clubroot is a subject that comes up with an increasing frequency in conversations between canola growers. It’s a topic that demands the attention of anyone growing canola, since it can have a devastating impact on a canola crop, according to Venkat Chapara, the plant pathologist at the Langdon Research Extension Center who specializes in clubroot research.

The clubroot pathogen causes swellings, also known as galls, to form on the canola roots. These galls ultimately causes premature death of the plant.

The beginning – where did problem begin?

Clubroot was first discovered in Cavalier County, N.D., in 2013, however the disease was first detected in Alberta, Canada in 2003. Plant breeders in Canada started working on clubroot resistant canola varieties at that time, and the first resistant variety came on the market in 2009.

“Until then the farmers had suffered a lot and they had thought the problem was solved with resistant canola varieties,” Chapara said. “But in 2013 they found clubroot again in the resistant varieties, since the clubroot pathogen had mutated and the resistant varieties were no longer working.

The clubroot pathogen is difficult to control since it exhibits characteristics from three different organisms – a fungi, a slime mold and a protozoa. The pathogen is spread through contaminated soil, much like the soybean cyst nematode (SCN), but SCN is more simplistic since it involves only one organism. Canola fields hit with the clubroot pathogen can experience losses ranging from 50-75 percent.

Chapara started surveying canola fields in Cavalier and several adjacent counties in 2016 for clubroot. That year only one field out of 49 sample tested positive for clubroot. The following year 60 fields were sampled with six showing positive returns and last year, 2018, samples were taken in 100 fields, with 33 showing positive results. So far all of the clubroot positive fields have been located in Cavalier County and in areas with a soil pH of less than 7.

Controlling the spread of clubroot

There are currently two methods of keeping the clubroot pathogen in check – the use of resistant varieties and the use of soil amendments that increases the soil pH above a level of 7 and preventing the soil from one field contaminating another field by cleaning equipment between fields.

Resistant varieties – Earlier it was mentioned that clubroot had mutated to resistant varieties of canola, but since then work has been done to develop new resistance strains. In fact, by 2018 Canadian plant breeders have included up to five different resistance genes in a single variety. However, varieties currently available in the U.S. contain only one resistant gene against clubroot.  Growers must be careful in the use of clubroot resistance.

“The maximum you can use a resistant variety in a five-year period is two times, and actually the recommended time is only one in five years,” Chapara said.

And if you don’t have any evidence of clubroot on your farm, it is a waste of money to plant a clubroot resistant variety.

The important soil factor - Some may think since their soil pH level is generally 7 or higher they don’t need to be concerned about clubroot. But Chapara cautions that soil pH isn’t uniform across an entire field and those areas in a field with a soil pH of less than 7 run the risk of clubroot being established.

Thus far no clubroot problems have been found in soils with a pH of 7 or higher. However, in his survey methods, he is tracking the pH levels of the soils they are testing and presence or absence of the clubroot pathogen. By doing this, he will be able to detect if the clubroot pathogen is starting to mutate and start to populate the higher pH soils.

Cleaning equipment between fields is an important step in controlling the spread of clubroot.

“If you clean your equipment after you are done in the clubroot field, you can minimize the spread of the pathogen by 90 percent,” Chapara said.

Determining your clubroot situation

Everyone growing canola needs to be aware of this devasting pathogen and the methods that can be used to determine if there is a clubroot problem.

Soil tests – Soil tests are available through NDSU to determine the number of clubroot spores in a soil sample. Soils with 18,000 spores, or more per gram of soil, are considered to be infected with clubroot, even though galls may not appear on the canola roots. However, at these levels, it would be recommended to plant a clubroot resistant canola variety.

Canola plant symptoms – When plants start to flower, growers should be alert for areas where the flowers aren’t as brightly yellow as the rest of the field or later in the growing season it will appear as brown areas in the healthy green canola plants. Some plants can be pulled from those areas and the roots examined for the presence of galls.

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LANGDON, N.D. – Clubroot is a subject that comes up with an increasing frequency in conversations between canola growers. It’s a topic that demands the attention of anyone growing canola, since it can have a devastating impact on a canola crop, according to Venkat Chapara, the plant pathologist at the Langdon Research Extension Center who specializes in clubroot research.

The clubroot pathogen causes swellings, also known as galls, to form on the canola roots. These galls ultimately causes premature death of the plant.

The beginning – where did problem begin?

Clubroot was first discovered in Cavalier County, N.D., in 2013, however the disease was first detected in Alberta, Canada in 2003. Plant breeders in Canada started working on clubroot resistant canola varieties at that time, and the first resistant variety came on the market in 2009.

“Until then the farmers had suffered a lot and they had thought the problem was solved with resistant canola varieties,” Chapara said. “But in 2013 they found clubroot again in the resistant varieties, since the clubroot pathogen had mutated and the resistant varieties were no longer working.

The clubroot pathogen is difficult to control since it exhibits characteristics from three different organisms – a fungi, a slime mold and a protozoa. The pathogen is spread through contaminated soil, much like the soybean cyst nematode (SCN), but SCN is more simplistic since it involves only one organism. Canola fields hit with the clubroot pathogen can experience losses ranging from 50-75 percent.

Chapara started surveying canola fields in Cavalier and several adjacent counties in 2016 for clubroot. That year only one field out of 49 sample tested positive for clubroot. The following year 60 fields were sampled with six showing positive returns and last year, 2018, samples were taken in 100 fields, with 33 showing positive results. So far all of the clubroot positive fields have been located in Cavalier County and in areas with a soil pH of less than 7.

Controlling the spread of clubroot

There are currently two methods of keeping the clubroot pathogen in check – the use of resistant varieties and the use of soil amendments that increases the soil pH above a level of 7 and preventing the soil from one field contaminating another field by cleaning equipment between fields.

Resistant varieties – Earlier it was mentioned that clubroot had mutated to resistant varieties of canola, but since then work has been done to develop new resistance strains. In fact, by 2018 Canadian plant breeders have included up to five different resistance genes in a single variety. However, varieties currently available in the U.S. contain only one resistant gene against clubroot.  Growers must be careful in the use of clubroot resistance.

“The maximum you can use a resistant variety in a five-year period is two times, and actually the recommended time is only one in five years,” Chapara said.

And if you don’t have any evidence of clubroot on your farm, it is a waste of money to plant a clubroot resistant variety.

The important soil factor - Some may think since their soil pH level is generally 7 or higher they don’t need to be concerned about clubroot. But Chapara cautions that soil pH isn’t uniform across an entire field and those areas in a field with a soil pH of less than 7 run the risk of clubroot being established.

Thus far no clubroot problems have been found in soils with a pH of 7 or higher. However, in his survey methods, he is tracking the pH levels of the soils they are testing and presence or absence of the clubroot pathogen. By doing this, he will be able to detect if the clubroot pathogen is starting to mutate and start to populate the higher pH soils.

Cleaning equipment between fields is an important step in controlling the spread of clubroot.

“If you clean your equipment after you are done in the clubroot field, you can minimize the spread of the pathogen by 90 percent,” Chapara said.

Determining your clubroot situation

Everyone growing canola needs to be aware of this devasting pathogen and the methods that can be used to determine if there is a clubroot problem.

Soil tests – Soil tests are available through NDSU to determine the number of clubroot spores in a soil sample. Soils with 18,000 spores, or more per gram of soil, are considered to be infected with clubroot, even though galls may not appear on the canola roots. However, at these levels, it would be recommended to plant a clubroot resistant canola variety.

Canola plant symptoms – When plants start to flower, growers should be alert for areas where the flowers aren’t as brightly yellow as the rest of the field or later in the growing season it will appear as brown areas in the healthy green canola plants. Some plants can be pulled from those areas and the roots examined for the presence of galls.

Once it is determined you have plants with galls, an effort should be made to destroy those plants as soon as possible, Chapara noted. If the canola plant is left until the normal harvest time, those galls will have ruptured and sent millions of spores from each plant into the soil.

If there are just a few small patches, he suggests pulling the infected plants along with their roots and burn the plant. Those areas found late in the season or involving larger areas should be left undisturbed at harvest time so as to minimize the spread of the spores produced by the galls.

Those wanting more information on clubroot can contact Chapara by calling the Langdon REC at 701-256-2582, his cell phone at 701-566-3685 or by email at venkata.chapara@ndsu.edu.

nce it is determined you have plants with galls, an effort should be made to destroy those plants as soon as possible, Chapara noted. If the canola plant is left until the normal harvest time, those galls will have ruptured and sent millions of spores from each plant into the soil.

If there are just a few small patches, he suggests pulling the infected plants along with their roots and burn the plant. Those areas found late in the season or involving larger areas should be left undisturbed at harvest time so as to minimize the spread of the spores produced by the galls.

Those wanting more information on clubroot can contact Chapara by calling the Langdon REC at 701-256-2582, his cell phone at 701-566-3685 or by email at venkata.chapara@ndsu.edu.