Top five things to know about clubroot
- Clubroot is a disease that affects plants in the cabbage family.
- Plants infected by clubroot are stunted, wilt easily, and may have yellowing leaves.
- Roots of clubroot infected plants are swollen into thick, irregular club shapes.
- Distribution of clubroot in Minnesota is unknown.
- Infected plants should be composted or buried on site.
All members of the cabbage family, brassicaceae, are susceptible to clubroot. This includes cabbage, cauliflower, broccoli, Brussels sprouts, kohlrabi, kale, radish, turnips, rutabaga, mustard greens, collard greens, arugula, bok choy, and canola.
The clubroot pathogen can infect the roots of some common weeds without causing symptoms.
- Plants are stunted
- Plants wilt with only slight drought stress
- Leaves may turn yellow
- Young plants may be killed
- Older plants fail to produce a harvestable head
- Roots are swollen and distorted into large clubs
- Smaller bulbous galls may be seen on secondary roots, or coming off a large taproot like a turnip
- Clubbed roots are firm and light colored early in the season
- Roots turn black and decay by the season's end
How clubroot spreads and survives
Clubroot is caused by the pathogen Plasmodiophora brassicae. It will not spread on seed, but it can be brought into a garden on infected transplants. The pathogen forms thick walled spores in infected roots. Spores are released into the soil as roots break down and can survive for 20 years.
Clubroot spores can be brought into a new area on infested soil or compost. Tools like tillers and shovels can spread the pathogen if not cleaned after use in infested soils. Spores can be moved short distances on wind strong enough to blow soil particles.
Prevention and management
- Grow plants from seed or purchase transplants from a reputable supplier. Inspect transplants for symptoms on roots prior to planting.
- Only add soil or compost that has been heated to kill pathogens. Soil should be treated with steam and compost should reach 148° F while composting.
- Remove all soil from tools and clean with a 1:9 solution of household bleach in water or with undiluted Lysol with the active ingredient .1% alkyl dimethylbenzyl ammonium saccharinate.
If clubroot is found in the garden
Once clubroot is found at a site, it is likely to be present at that site indefinitely. The management strategies below are designed to prevent the spread of the pathogen to a new location, and reduce the pathogen population to a low enough level to allow for some production. Heavily infested sites should not be planted with members of the cabbage family but can be used for other crops.
- Bury or compost infected plants on site.
- Remove soil from tools on site and disinfect tools with a 1:9 solution of household bleach in water or with undiluted Lysol with the active ingredient .1% alkyl dimethylbenzyl ammonium saccharinate before using them at another location.
- Do not grow any member of the cabbage family at the site for 5-7 years. This will reduce the pathogen population but not completely eliminate it.
- Remove all weeds during the crop rotation. The pathogen can survive on many weeds.
- Clubroot resistant varieties of cabbage are available. These varieties will perform best when planted after a period of 5-7 years during which no member of the cabbage family is grown at the infested site.
- Submit a soil sample to the UMN Soil Testing Laboratory to determine the soil pH of the garden. Apply lime to raise the pH to 7.3 -7.5.
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