VG01045 Bunching Vegetables – disease control

Downy mildew and white blister are the main foliage diseases of spring onions and radish respectively.

Growers report that these diseases can cause from 50 to 100% losses in a national industry worth an estimated $85 million annually.

Some growers have ceased production of spring onion and radish crops because of disease pressure from the two causal fungi Peronospora destructor (Berkeley) Caspary and Albugo candida (Pers.) Kuntze, respectively.

This three year study on downy mildew in spring onions evaluated prospects for the development of Integrated Management Strategies.

This involved research on: computer models and decision support systems, fungicides and irrigation scheduling, resistant varieties and nutrition.

An economic analysis also appraised the cost effectiveness of proposed treatments for use by growers.

Studies on white blister were more restricted. They targeted the evaluation of fungicides and the risk of transmission of A candida in seed.

Elizabeth Minchinton Victor Galea
Fiona Thomson Lindsay Trapnell
Craig Murdoch Savitri Nadesan
Narelle Kita

Disease management strategies for downy mildew on spring onions and white blister on radish- 2005
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Recommendations :

Three improved control strategies have been developed for downy mildew and offered to growers of spring onions:

  1. The use of decision support systems linked to computer models that analyse prevailing temperature, rainfall, relative humidity and predict the need to apply control treatments.
  2. New foliar spray schedules have been designed which incorporate the combination of new and old fungicides. When used correctly these can reduce disease to negligible levels and minimise the risk of resistance to fungicides.
  3. The use of early morning overhead irrigation as a supplementary control measure, suppresses spore production by the fungus and can be integrated with foliar spray programs.

Research showed some varieties were less susceptible to downy mildew than others. It also found the disease could not be controlled by modification of nutrient treatments, despite nutrient amendments producing a better quality onion.

One specific control strategy was developed for white blister and offered to growers of radish crops.

  • New foliar spray schedules have been designed which incorporate combinations of new and old fungicides.
    These effectively control disease and minimise the risk of resistance to fungicides.

Limited surveys did not demonstrate seed borne infection by the white blister fungus. The implications are that it is unlikely that epidemics of white blister are caused by planting infected seed.

It is more likely that these originate from resistant spores, which survive in soils or from the carryover of spores from other radish crops.

The consequence is that, on the basis of current data, seed treatment by heat or fungicides is not considered a high priority.

Much of the information from the research is presented in a booklet ” A guide to diseases and disorders of bunching vegetables in Australia “ , which has been distributed nationally to industry through the Industry Development Officer Network.

Acknowledgments :

The researchers acknowledge the financial support for this project from Horticulture Australia Limited (HAL), AUSVEG, the Federal Government and the Department of Primary Industries, Victoria.

The authors thank the members of the steering committee, Craig Arnott, Peter Cochrane, Geoff Foster, Tony Lamattina, Rocky Lamattina and Karl Riedel for their valuable contribution to this project.

The authors thank the growers whom supplied their crops for field trials, reported in this report.

The authors also thank the Vegetable Industry Development Officers for their assistance with the project.

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