Benchmarking predictive models, nutrients and irrigation for management of downy and powdery mildews and white blister (VG07070)

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Please note that as these reports may date back as far as the 1990s, the content and recommendations within them may be superseded by more recent research.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?

This project focused on white blister on brassicas, powdery mildew on cucurbits and downy mildew and anthracnose on lettuce. The project determined the efficacy and economics which could be achieved with weekly fungicide sprays, disease predictive models, irrigation timing and growing a resistant variety, but the latter was the most superior IPM tool. It evaluated the benefits of nutrient management; developed a disease predictive model for powdery mildew of cucurbits and a detection kit for airborne spores of white blister.

Major outcomes of the research 

• White Blister of brassicas:

The world’s first white blister spore detection kit was developed for use with the white blister disease predictive model (Brassicaspot™). This detection kit was a major addition to the current disease control tools. Scientific and economic analysis of field trials demonstrated that the number of fungicide spray applications based on predictions of the Brassicaspot™ model could be reduced by 12-13, which corresponded to a 77 per cent reduction in disease on broccoli heads and an increase in profits of 13 per cent, during dry conditions. Irrigating broccoli crops in the morning rather than the evening reduced disease by 58 per cent and increased profit by 3 per cent. Growing a broccoli variety with resistance to white blister reduced disease by 99 per cent and increased profit 11 per cent.

• Downy mildew of lettuce:

A disease predictive model for downy mildew on lettuce (BREMCAST™) showed timing fungicide sprays based on model predictions could reduce spray programs by 1-3, reduce disease by 50-70 per cent and increase profits by 20 per cent. High rates of calcium nitrate applied to lettuce seedlings reduced susceptibility to downy mildew and anthracnose.

• Powdery mildew:

The world’s first powdery mildew disease predictive model (PMRI) for powdery mildew of cucurbits grown under Australian conditions was developed and a preliminary trial indicated a reduction of one spray could be achieved.

This project was part of the HAL Plant Pathology Program and the commissioned research was undertaken with the support of HAL; the Federal Government; the Department of Primary Industries, Victoria; and The University of Queensland.

Recommendations for future research and development

• Downy mildew of lettuce: Format the BREMCAST™ model into user-friendly software and validate it in the field.
• White blister: Under Australian conditions test the white blister spore detection kit alone and incombination with the Brassicaspot™ model; investigate modifications to the models spray threshold and determine the physiological stage when broccoli heads are susceptible to white blister infection.
• Powdery mildew of cucurbits: Further refine the cucurbit powdery mildew disease predictive model and test it on commercial crops.

Recommendations to industry

To maximize the production of broccoli, lettuce and cucurbits and meet the high aesthetic standards of the marketplace:

• Where possible grow resistant varieties, although they still need to be sprayed.
• Irrigate broccoli crops at 4 am instead of 8 pm to reduce the incidence of white blister.
• Spray Chinese cabbage with fungicides 14 days before harvest to control white blister.
• Use calcium nitrate based fertilizers instead of ammonium or potassium based fertilisers.
• Use disease predictive models as decision support tools, especially during dry conditions.