Science Into Practice - Monitoring for downy mildew

Impatiens downy mildew, which is caused by Plasmopara obducens, is a foliar disease that is specific to impatiens.

During early 2011, a strain that is resistant to the fungicide metalaxyl-M was introduced into commercial impatiens production, which resulted in downy mildew infections that were difficult to control.

To minimise the risk posed by the resistant strain, steps were taken to restrict the level of cuttings-raised impatiens production. No infections caused by the resistant strain were detected by the Food & Environment Research Agency (FERA) in 2012 (as monitored in previous project PO 011), suggesting that the action had been successful, but the risk remains.

Project P0 011a is continuing the monitoring of metalaxyl-M resistance over a six-year period. Early warning of resistance will help growers to decide on the most suitable spray programmes to adopt for their crops.

The monitoring will also provide information on the prevalence, persistence and geographical location of the metalaxyl-M resistant strain in the wider environment. P. obducens was not found on any of the plant samples that were submitted to FERA in 2013.

"As the disease has now become an international problem, the continued monitoring of any outbreaks is important to provide guidance for strategic production decisions made by the industry from year to year," says Mike Smith of WD Smith & Son.

The full grower summary for project P0 011a can be found on the HDC's website at

Horticultural Development Company

For details on all HDC activity, visit

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