Symptoms: Affecting members of the cabbage family, club root is a serious plant disease in North America. It is caused by the soil-borne fungus, Plasmodiophora brassicae, which infects susceptible plants through root hairs. Diseased roots become misshapen and deformed (clubbed), often cracking and rotting. As a result, plants have difficulty absorbing water and nutrients properly. They may grow slowly and wilt during the heat of the day; plants often revive during cool nights. Outer leaves eventually turn yellow or brown. Club root will reduce yields and can cause total plant loss.
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 degrees F. Spores can survive in the soil for as many as 10 years.
Control: Choose resistant cultivars when possible. Try to prevent the occurrence of this disease by keeping a clean garden and rotating crops. Keep in mind that the disease spores can persist in the soil for many years. If club root is present, you may want to solarize the soil*. Carefully remove infected plants and sterilize garden tools (one part bleach to 4 parts water) after use. Raise your garden soil’s pH to a more alkaline 7.2 by mixing oyster shell lime into it in fall. Check soil 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.
Photo Credit: County of Newell (Alberta, Canada)