Club root, also known as swollen fingers amongst other names is a serious fungal mould type of disease caused by the soil-borne fungus Plasmodiophora brassicae which infects susceptible plants through root hairs.
The diseased roots become swollen, misshapen and deformed (clubbed) often cracking and rotting. As a result, plants develop difficulties in absorbing water and nutrients.
Oftenly, crops grow poorly and wilt during the heat of the day and can revive during cool nights.
Club root disease reduce yields and can cause total crop failure.
The disease is restricted mainly to members of the cruciferous family, both cultivated and weeds, and to a few other plants, which can be grouped as follows:
- Most susceptible; cabbage, Chinese cabbage, Brusselss sprouts, some turnips etc
- Medium susceptible; kale, cauliflower, collards,broccoli, some turnips and radishes etc
- Mildly susceptible; canola, black mustard, some turnip and radish varieties etc
- brassicae is capable of surviving in the soil for 7-10 years or longer as resting spores.
Disease development is favored by high soil moisture and soil temperatures between 18°-25° C and it is primarily associated with acid soils. Within the infected crop roots, the organism develops rapidly, causing an increase in the number and size of cells, which results in “clubbing.” During the development of the organism in the plant, new zoospores are produced, which are capable of infecting the same plant or adjacent plants and, thus, repeating the cycle. Eventually, resting spores are formed within the diseased plant tissue, and these are released into the soil when the crop roots disintegrate.
The disease is not seed-borne, but, the fungus is readily spread in surface runoff water, irrigation water, contaminated equipment, and to some extent by roving animals.
The use of contaminated transplants is the chief means of spread of the causal agent.
Clubroot may develop extensively on plant roots before the first sign (an abnormal wilting and yellowing of leaves, especially on warm days) is noticed aboveground. If the soil is moist, these symptoms may not become apparent until water stress occurs.
If infection occurs at an early stage of growth, young crops become stunted and may die, whereas plants infected in a later stage do not make marketable heads or growth.
When diseased plants are pulled from the soil, the roots are usually swollen and distorted.
Root malformation may vary in size from very small swellings on the tap and lateral roots to large club-shaped roots, depending on when the crops became infected.
Besides reducing the plant’s ability to take up water, the clubbed tissue fails to develop a protective outer layer and, thus, is susceptible to invasion by other infections like soft rot.
The infected plants initially appear normal, but as they mature, they become unthrifty, grow slowly, wilt during sunny days and become stunted. The disease first appears in the field in scattered groups of a few to many plants but in successive seasons, the entire field may become infected.
For an effective control of the disease, systemic fungicides should be drenched into the soil.
These fungicides include the following;
- CHANCETYL ELITE 800WDG
- TRINITY GOLD 452WP
- COLONIZER 440WP
- DOMAIN 250EC
- EXCEMPO CURVE 250SC
- GREEN COP 500WP
- GEARLOCK TURBO 250WP
- MILLIONAIRE 690WDG
- PYRAMID 700WP
- Choose resistant cultivars when possible.
- Practise rotations with non-host crops for an interval of 3-5years.
- Ensure proper weed control (weeds harbour diseases)
- Carefully remove infected plants.
- Sterilize garden tools after use
- Stabilise the soil’s pH by mixing basal fertilizers with HUMIPOWER during application.
- Solarize the soil, which reduces or eliminates many soil inhabiting pathogens.
- Always use disease free planting materials.
- Ensure timely control of the disease.
- Alternate different chemicals to prevent resistance build up by the fungus.
- Maintain a proper crop nutrition.