Clubroot

Wikipedia:

Clubroot is a common disease of cabbages, radishes, turnips, [[canola] and other plants belonging to the family Cruciferae (mustard family). It is caused by Plasmodiophora brassicae, which was once considered a slime mold but is now put in the group Phytomyxea. It has as many as thirteen races. Gall formation or distortion takes place on latent roots and gives the shape of a club or spindle. In the cabbage such attacks on the roots cause undeveloped heads or a failure to head at all, followed often by decline in vigor or by death. It is an important disease, affecting an estimated 10% of the total cultured area worldwide.

Historical reports of clubroot date back to the 13th century in Europe. In the late 19th century, a severe epidemic of clubroot destroyed large proportions of the cabbage crop in St. Petersburg. The Russian scientist Mikhail Woronin eventually identified the cause of clubroot as a "plasmodiophorous organism" in 1875, and gave it the name Plasmodiophora brassicae.

In 18th, 19th and early 20th century Britain clubroot was sometimes called finger and toe, fingers and toes, anbury, or ambury, these last two also meaning a soft tumor on a horse.

The potential of cultural practices to reduce crop losses due to clubroot are limited, and chemical treatments to control the fungus are either banned due to environmental regulations or are not cost effective. Breeding of resistant cultivars therefore is a promising alternative.

Alberta Canola Infestation

In 2003 clubroot was identified in Alberta as an outbreak in canola crops in the central area of the province mainly isolated to the Edmonton area. Clubroot is a soilborne disease caused by the biotrophic protist Plasmodiophora brassica. The infection causes the formation of large galls on the roots which look like clubs. These formations impede nutrient and water uptake and can cause plant death, wiping out important money generating canola crops. Initially 12 commercial fields of canola were identified, but that number grew to over 400 by 2008.

In 2007 Alberta declared P.brassicae a pest via the foundation legislation in hopes to help contain spread of the disease.

The Pathotype 3, is the predominant source for Alberta outbreaks. Studies showed that out of the 13 strains of P. brassicae, the most virulent form is dominant in Alberta.

Studies have shown that infestation numbers are highest at common field entrances and decline as you move further into the field, away from the entrance. From these results, it was concluded that infested soil on farm machinery was increasing spread of the pathogen. Some natural field to field spread is starting to be seen

Liming has been an effective control measure to curb clubroot since the 19th century. This method does not eradicate clubroot but it will slow its development by creating unfavorable conditions. In addition, Calcium and Magnesium can be added to the nutrition profile of the soil to help control clubroot. To get efficient results the field soil [pH] must be kept above 7.5. This takes massive applications to field soil in order to effect all of the soil where spores of clubroot are found. Combining lime with one other treatment has shown most effective.

Several strains of canola have been tried, including European winter canola cv. Mendel (Brassica napus L.), as a clubroot resistance crop. It has been found that few cultivators exist. Specific genotypes do exist, of the Mendel strain, which could be a solution for canola crops in the Canadian prairies.

Crop rotation with non-host crops is another method help prevent club root. The half life of P. Brassicae is 3.6 years. Unfortunately, long rotations of approximately 20 years are required in order to be effective. This is extremely difficult with typical canola rotations not being more than 3 years. Canola crop brings in high revenue to farmers. This would also require complete removal of crucification crops such as wild radish and mustard.

Some fungicide has been found to help with clubroot but it is very pricey and would take huge amounts to saturate the soil. The best way to prevent contamination between fields is to clean agriculture equipment and vehicles which have come in contact with club root before moving to a new field. All contaminated soil, equipment and tools must not be moved to clean-disease free fields. The best preventative method is field monitoring. Throughout the season plants should be monitored for early symptoms of club root. More research is being conducted for early detection of club root in fall soils.