ACCE$$ TO A$IA ASIAN VEGETABLES NEWSLETTER Issue No. 13, June 1997 (English Edition)

CLUBROOT, THE CURSE OF THE CRUCIFER INDUSTRY:
A CONCERN FOR GROWERS OF ASIAN VEGETABLES
(Caroline Donald and Ian Porter (03) 9210 9222)

Clubroot is caused by a soil borne fungus Plasmodiophora brassicae. The fungus infects cruciferous Asian vegetables including Chinese cabbage, Chinese chard (pak choy), Baby Chinese Chard (Baby pak choy), Shanghai Chinese chard (Shanghai pak choy), Baby Flowering Chinese Cabbage, Chinese Broccoli, Chinese Flowering Cabbage, Mustard Green, White Flowering Cabbage, Chinese radish and Green radish. It also infects broccoli, cauliflower and other brassicas.

Clubroot on brocooli roots	Normal broccoli roots
In Victoria, we have seen clubroot in Chinese cabbage particularly the rocket type, Shanghai Chinese chard, Chinese broccoli and Chinese flowering cabbage. Editors

Infection occurs on the roots at any stage of growth. Symptoms do not become obvious until typical knotted swellings form on the roots. The first above ground symptom of disease is usually wilting, particularly during hot dry weather. Severely diseased plants are generally stunted and the foliage may be different in colour from healthy plants. Crop losses are most severe for crops planted between October and April. The disease rarely affects winter sown crops in southern Australia.

Infected roots contain millions of fungal spores. After the roots decay, these spores are released into the soil where they can remain alive but resting for up to twenty years. When conditions are right (high soil moisture), the spores infect and subsequently disease development is most pronounced in warm (20-25oC), acidic soils (pH less than 7).

KEEPING CLUBROOT OUT OF YOUR CROPS

The fungus can be spread on or in anything that may carry contaminated soil from place to place. Farm machinery, boots, animals, infected transplants, contaminated irrigation water and surface flood water are all important means of spread. Management practices that can be used to reduce build up and spread of disease include:

Seedlings

• Use only disease-free transplants obtained in a pasteurised
  soil-mix, or from an open seed bed which is disease-free or
  pretreated with appropriate fumigants.
• If growing on transplantsIsolate seedbed, maintain free of
  cruciferous weeds and avoid contaminating the area with
  diseased soil or water.

• Rotate cruciferous Asian vegetables with non cruciferous
  crops as often as practical.
• Avoid cropping crucifers more than once every two years
  in infested sites.
• Clean machinery thoroughly before moving all equipment
  from infested fields to non-infested fields.
• mprove drainage in poorly drained soils and low lying
  areas.
• Do not use water from dams receiving run-off from infested
  fields.
• Sow crops into paddocks suspected of being infested with
  clubroot in winter months only.
• Add lime to acid soils to increase soil pH to 7.0-7.5.
• Practice weed control.
• Dispose properly or burn diseased material.
• Do not throw infested seedlings near waterways or dams;
  use waste dumps or other industrial waste facilities.

CLUBROOT RESEARCH IN AUSTRALIA

A national research project coordinated from the Institute for Horticultural Development (Knoxfield) is developing clubroot control strategies based on:

• liming responsive soils to increase pH to 7.0-7.5
• increasing soil concentrations of beneficial plant nutrients (calcium, boron and magnesium)
• strategically applying high analysis fertilisers and fungicides into transplant rows.

If you plan to grow any of the Asian vegetables listed in this article (particularly Chinese cabbage) on clubroot infested land this summer and are willing to help us further develop existing control strategies for the Asian vegetable industry, please contact Caroline Donald or Ian Porter (03) 9210 9222.