Cabbage Integrated Pest Management : An Ecological Guide.

Major Diseases of Cabbagebut does not look severely infected, it is possible to leave it in the field until the harvest. During harvesttime, uproot the whole plant and if the roots of the plant are affected, take those plant parts aside fordrying and burning afterwards. Don’t leave infected plants in the field. Severely infected plants will notform a head and should be removed from the field. See section below on management and control.Natural enemies/antagonistsBiological control of clubroot with Trichoderma sp. may become an option in the future. In studies withChinese cabbage in New Zealand for example, seventeen of the 25 isolates of Trichoderma sp. reducedclubroot severity compared to the untreated control. Field trial results with two Trichoderma isolates,applied as a root dip before transplanting, gave reduction of club weight on roots but did not increase thetop weights of the plant. L(Cheah et al, 1996, www28).Management & control practicesPrevention activities:· Resistant varieties: some differences in susceptibility between varieties has been reported but it isadvisable to test varieties at local conditions, for example in varietal trials.· Select clubroot-free nursery soil that is well drained. The preferred nursery has not grown crucifersfor many years.· Because clubroot is so long-lived, crop rotation is probably not effective. Fields once severely infectedwith the clubroot pathogen remain so indefinitely and become unfit for cultivation of brassicas.· Raising soil pH to a neutral level of around pH 7 by broadcasting and incorporating hydrated lime intothe soil offers some control/protection. This liming should not be done more than once every 3 yearsto keep the soil from becoming too alkaline, nor is it very effective on light, sandy soils. Guidelines toraise the pH are given in section 3.4.6.· Use healthy seedlings. Do not transplant seedlings that have little clubs or swollen roots that do notlook normal. In fact, no plants from a seedbed that has even a single clubroot seedling in it, shouldbe transplanted into a disease-free field! if any transplants have clubroot symptoms, many others arecertain to be infected, even though symptoms may not yet have appeared!· Remove weeds, there are many cruciferous weeds that can be a host of clubroot and other cabbagediseases.· Be careful with fields of other farmers that do have a clubroot infection. If you visit an infected field,make sure there is no soil attached to your slippers, shoes or farm tools when you return to your ownfield. You can easily transport the disease with the soil particles!It was noted that some farmers, who had serious clubroot problemsin their field, could easily recognize clubroot infected plantsby the small plant size. But instead of roguing the plants, theyapplied foliar fertilizer to these small plants in an attempt to get atleast a little head from these small plants. However, comparing thecosts of a foliar fertilizer (quite expensive!) to the additional income of a few small,low quality heads AND the risk of giving the pathogen a chance to multiply, and spread into otherparts of the field, make this practice not very attractive.Remove infected plants: they will not give you much yield (and income) and infected plants in thefield will lead to MORE disease!165 Cabbage Ecological Guide - 2000