This is a final research report from Hort Innovation’s historical archives. Please note that as these reports may date back as far as the 1990s, the content and recommendations within them may be superseded by more recent research.

What was it all about?

Clubroot was the most serious disease of the vegetable brassica crops including broccoli, cauliflower, cabbage, Brussels sprouts, Chinese cabbage and other Asian vegetable brassicas. In Australia it was estimated that the disease was responsible for losses of 5-10 per cent of the national crop, or approximately $10m annually.

This project, a national initiative involving researchers from 5 states of Australia, had sought to address the short, medium and long-term needs of the brassica industry to manage this disease by:

1. Identifying treatments that control clubroot
2. Developing more effective and sustainable methods of using these treatments
3. Developing integrated management strategies that were effective in all states
4. Deteffllining the extent of variation in the pathogen population and the potential for use of tolerant crop varieties in Australia.

In the short term metham sodium (500 L/ha) was used to control spot outbreaks, and limit further spread of the disease in recently affected regions at the time. Long-term management strategies were developed based on:

• Good fann hygiene
• Crop rotation
• Timing responsive soils to pH 7.0-7.5
• Maintaining high soil calcium in the first 3 weeks post-transplanting
• Applying a preventative fungicide (fluazinam, Shirlan® 3 L/ba).

Recommendations arising from this work were summarised and distributed to brassica growers nationally in the pamphlet "A guide to the prevention and management of clubroot in vegetable brassica crops. A method of incorporation of treatments into the transplant row was developed and had:

• Reduced the cost of treatments such as calcium cyanamide by approximately two thirds
• Improved the distribution and efficacy of fluazinam, doubling yields of conventionally treated plants in some soil types
• Minimised the impact of residues from treatments on the environment

This method of application became the most effective method of application of fluazinam (Shirlan®) and the most cost effective method of applying calciwn cyanamide (Perlka®) for clubroot control. It had also been used to improve fertiliser use efficiency and had increased yields of winter grown cauliflowers by 10 t/ha.

The pathogen population in Australia was found to consist of a number of distinct pathotypes of P. brassicae. Two varieties of broccoli (Yates '573 7' and Dome,) were tolerant of some, but not all of these pathotypes. 'Dome' was commercially available in Australia.

Clubroot was now able to be managed in the majority of Australian horticultural soils. The challenge remained to predict anticipated productivity tosses from soil inoculum loads thereby enabling growers to choose the most cost-effective management strategy based on a simple soil test.