An integrated approach to the control of clubroot in vegetable Brassica crops

This paper reviews the approaches used internationally to control clubroot and details the way that these approaches have been developed and their use integrated in Australia to provide a multifaceted or 'whole of production' program for managing this disease. In Australia, an integrated program to control and prevent the spread of clubroot has been developed based on detection and quantification of P. brassicae, improved farm and nursery hygiene and strategic application of in-field controls including lime (calcium oxide), calcium, boron and the fungicide fluazinam. A nested PCR assay has been developed and used in seedling nurseries, to identify entry points for P. brassicae including dust, water and soil and root debris on reusable plastic trays. In the field a range of chemical and non-chemical soil treatments have been used alone (on low risk sites) or as part of an integrated control strategy (moderate to high-risk sites) to manage clubroot. In field trials conducted over a 5-year period, manipulation of soil pH using lime (calcium oxide) was generally sufficient to prevent significant yield loss on low risk sites. On moderate to high-risk sites, additional protection in the form of calcium and boron and/or a protectant fungicide such as fluazinam was required to prevent disease. However, integration of two or more treatments, was cost effective only when the soil pH was low. On a high pH site, incorporation of fluazinam into the transplant row at 1.5 kg a.i./ha was the most effective treatment and there was no additional benefit, in terms of dollar returns, of applying additional treatments. New machines were developed to incorporate these treatments into the root zone of the transplants in bands along the planting rows. This method of application improved the efficacy of the fungicide fluazinam, increasing yields of broccoli and cauliflower by 80%, and reduced the cost of lime and calcium cyanamide treatments by 66%. To assist growers to select the most cost effective management strategy a real-time PCR has been used to quantify the inoculum load in farm soils and predict expected yield loss. The program now offers Australian vegetable brassica growers a complete management package for clubroot.