Disease management strategies for the production of bunching vegetables (VG01045)

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note that as these reports may date back as far as the 1990s, the content and recommendations within them may be superseded by more recent research.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

Research had identified new and improved methods for controlling damaging diseases of spring onion and radish crops in Australia. The total national value of the two industries in Australia was estimated at $85 million annually and economic consequences for growers had the potential to be considerable.

The diseases, known as downy mildew and white blister, were caused by two different microscopic fungi that infected and killed leaves. The problem was significant because it had curtailed winter production of spring onions and, in many cases, totally prevented growing of radish crops.

The research by scientists at DPI’s Knoxfield Centre was supported by funds from the Vegetable Industry, Hort Innovation (which was then Horticulture Australia Limited) and the Department of Primary Industries Victoria.

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

1. The use of decision support systems linked to computer models that analysed prevailing temperature, rainfall, relative humidity and predicted the need to apply control treatments.
2. New foliar spray schedules were designed which incorporated the combination of new and old fungicides. When used correctly these reduced disease to negligible levels and minimised the risk of resistance to fungicides.
3. The use of early morning overhead irrigation as a supplementary control measure, suppressed spore production by the fungus and could 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:

1. New foliar spray schedules were designed which incorporated combinations of new and old fungicides. These effectively controlled disease and minimised the risk of resistance to fungicides.

Limited surveys did not demonstrate seed borne infection by the white blister fungus. The implications were that it was unlikely that epidemics of white blister were caused by planting infected seed. It was more likely that these originated from resistant spores, which survived in soils or from the carry-over of spores from other radish crops. The consequence was that, on the basis of data at the time, seed treatment by heat or fungicides was not considered a high priority.

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