Disease management strategies for downy mildew on spring onions and white blister on radish
Downy mildew and white blister are the main foliage diseases of spring onions and radish respectively. Growers report that these diseases can cause up to 50-100% losses in a national industry worth an estimated $85 million annually. During a 3-year research project, the work 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, 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 the disease-causing organism in seed. The findings were that it is unlikely that epidemics of white blister are caused by planting infected seed. For both crops, new foliar fungicide spray schedules were designed, incorporating combinations of new and old fungicides. These schedules effectively control the foliar diseases and minimise the risk of resistance to fungicides.