Club Root

Affecting most brassica crops (cabbage, broccoli, cauliflower, etc.), club root is a serious plant disease in North American home gardens. It is caused by the soil-borne fungus Plasmodiophora brassicae which infects susceptible plants through root hairs. Diseased roots become swollen, misshapen and deformed (clubbed) often cracking and rotting. As a result, plants have difficulty absorbing water and nutrients properly.

Plants often grow poorly and wilt during the heat of the day; plants often revive during cool nights. Outer leaves may turn yellow, purple or brown. Club root will reduce yields and can cause total crop failure.

Fungal spores can be spread by wind, water and garden tools. Disease development can occur over a wide range of conditions, but is favored by excessive moisture, low soil pH and soil temperatures between 64 and 77˚F. Spores can survive in the soil for as many as 10 years.

Treatment

1. Fungicides will NOT treat this soil-dwelling micro-organism.
2. Choose resistant cultivars when possible.
3. Try to prevent the occurrence of this disease by keeping a clean garden and rotating crops.
4. Keep in mind that the disease spores can persist in the soil for up to 20 years. If club root is present you may want to solarize the soil.*
5. Control susceptible weeds — mustard, radish, shepherd’s purse — that may be infected to reduce potential buildup of the disease.
6. Carefully remove infected plants and sterilize garden tools (one part bleach to 4 parts water) after use.
7. Raise your soil’s pH to a more alkaline 7.2 by mixing oyster shell or dolomite lime into your garden in the fall. Simple and affordable soil test kits are available to check pH often.

* To solarize your soil, you must leave a clear plastic tarp on the soil surface for 4-6 weeks during the hottest part of the year. Soil solarization will reduce or eliminate many soil inhabiting pests including nematodes, fungi, insects, weeds and weed seeds.