Usually appear in patches. Young plants wither and are stunted in growth, older leaves become yellow or turn reddish.
Cabbage clubroot [Plasmodiophora brassicae]
Cabbage clubroot - image 1
The resting spores of the fungus can survive for over 20 years in the soil. They germinate in wet soils and infect the roots of oilseed rape and other brassicas. They invade the root hairs and produce a multi-nucleated cellular body that develops into a spore case which releases zoospores. These enter the soil through root hairs and can cause a new infection. Others enter deeper into the root tissue and stimulate its rapid division. Typical galls develop. These clubs disintegrate when the plant decomposes or during soil management and release resting spores. The infection is promoted by acidic, moist soils low in calcium and with low ventilation.
Cabbages, oilseed rape grown in a short crop rotation). Any cruciferous plant (Brassicaceae) can serve as a host plant, e.g. yellow mustard, wild radish, shepherd's purse, field penny-cress.
Pattern of damage
Typical symptoms are irregular reddish-brown clubs with furrowed main and lateral root branch surfaces. The infected root tissue develops club-shaped growths (Picture 1). Initially, they are white and inside, hard and without any cavities; later they are gray and show signs of decay. The galls of the club root can be mistaken for galls caused by the cabbage gall weevil; however, in this case, feeding tunnels caused by the larvae can be seen in the inside.
Controlled crop rotation (crop rotation breaks of 3 to 4 years). Neutral pH of the soil. Ensure sufficient soil aeration and good water flow. Control cruciferous field weeds. Use resistant varieties.