Disease
Clubroot
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Watch for | Watch for in May | Watch for in June | Watch for in July | Watch for in August | Watch for in September | Watch for in October |
What it is
Clubroot is caused by a soil-dwelling organism that infects the roots of cabbages, kale, sprouts, swedes, turnips, radishes and their ornamental relatives such as wallflowers. Once land is contaminated, the problem stays put, which makes it one of the most frustrating diseases on allotments, especially on acid, poorly drained soils.
Symptoms
Above ground, plants look stunted and yellowish and wilt on warm afternoons, recovering a little overnight. Dig one up and the roots will be swollen into thick, knobbly clubs or finger-like galls instead of a fine network. Later in the season these swellings rot and smell unpleasant. Cabbage root fly can also cause wilting, but its damage shows as tunnelled, chewed roots with small white maggots, not galls.
Cause
The organism forms tough resting spores that can survive in soil for 15 years or more. In warm, moist soil they release swimming spores that enter root hairs and trigger the swelling. Acid, wet soil suits it best. It travels on boots, tools, manure, bought-in plants and soil stuck to wheelbarrows, and spreads within a plot in drainage water.
Control
There is no cure for an infected plant. Pull up affected brassicas with as much root as possible and bin them; never compost them. On infected ground, raise the soil pH towards slightly alkaline by applying garden lime in autumn or winter, testing first and allowing a few weeks before planting. Improving drainage with organic matter or raised beds helps a great deal. No chemical treatment is available to home gardeners.
Prevention
Rotate brassicas so they do not return to the same bed for several years, and control cruciferous weeds such as shepherd's purse. Raise transplants in clean compost in large pots, so they have a good root system before going out. Clean boots and tools after working infected beds, and look for clubroot-resistant varieties of cabbage, sprouts, kale and swede.
Plants often affected
Could it be something else?
These problems share some of the same symptoms. Compare them, or run the symptom checker with these signs ticked.
Months to keep an eye out: May, June, July, August, September and October.
Sources
Identification and life-cycle details were checked against the references below. Text and advice are our own. See our editorial policy.