Clubroot of Crucifers
Pest Management Fact Sheet #5096
Clubroot is a serious disease of crucifers caused by the primitive fungus, Plasmodiophora brassicae. It is worldwide in occurrence having been spread by the activities of man.
The first symptom usually observed is a wilting of the foliage especially on hot days. Wilting is the result of impaired root function which reduces the capacity of the plant to take up water. The diseased roots are also less able to absorb nutrients and so the foliage may appear yellowish and the plant may be stunted. Although these above-ground symptoms could be due to other causes (e.g. cabbage maggot), an abnormal enlargement of the roots is diagnostic for this disease. The fungus penetrates the roots directly or through wounds and induces the root cells to enlarge. The resulting enlarged roots appear spindle-shaped, knobby, spherical, or club-shaped. All roots including the underground stem may be affected.
Soils that are cool and wet favor the disease and its survival. Especially important is the pH of the soil. Germination of the fungus spores is inhibited in alkaline soils. Conversely, acid conditions favor the disease.
Survival and Dispersal
Once the soil is infested by the clubroot fungus, the fungus will remain viable for years. It can live for 10 years in the absence of its host and, because it infects cruciferous weeds, it is likely to be present even longer. The infected roots eventually disintegrate in the soil releasing masses of spores. These long-lived spores can be transported in any manner that transports soil through the field. Soil can be carried on shoes, tools, farm equipment, runoff, splashing water, wind, etc. Although the disease is not seed born, it is readily carried on infected transplants.
- A four year rotation for cole crops is currently recommended unless club root is detected, then opt for a seven year rotation. Because the spores are so long-lived, rotation may only be marginally effective.
- Maintain the soil pH at least at 6.8, preferably above 7.2. This high pH may adversely affect some rotation crops. Add at least 1500 lb/acre of hydrated lime when planting in clubroot infested soils that are pH 7.0 and above. Lower pH may require more hydrated lime. Apply the lime at least 6 weeks before setting out the crop.
- Grow or buy clean transplants to avoid the initial infestation. Seedbeds should be well-drained and disease-free.
- PCNB (Terraclor 75WP) can be applied as a solution in the transplant water (2-6 lb/100 gal; 1 cup of solution per plant) or applied at the rate of 30lb/acre.
When Using Pesticides
ALWAYS FOLLOW LABEL DIRECTIONS!
Pest Management Unit
Cooperative Extension Diagnostic and Research Laboratory
17 Godfrey Drive, Orono, ME 04473-1295
1.800.287.0279 (in Maine)
Information in this publication is provided purely for educational purposes. No responsibility is assumed for any problems associated with the use of products or services mentioned. No endorsement of products or companies is intended, nor is criticism of unnamed products or companies implied.
Call 800.287.0274 (in Maine), or 207.581.3188, for information on publications and program offerings from University of Maine Cooperative Extension, or visit extension.umaine.edu.
The University of Maine is an EEO/AA employer, and does not discriminate on the grounds of race, color, religion, sex, sexual orientation, transgender status, gender expression, national origin, citizenship status, age, disability, genetic information or veteran’s status in employment, education, and all other programs and activities. The following person has been designated to handle inquiries regarding non-discrimination policies: Sarah E. Harebo, Director of Equal Opportunity, 101 North Stevens Hall, University of Maine, Orono, ME 04469-5754, 207.581.1226, TTY 711 (Maine Relay System).