Science Into Practice - Understanding downy mildew on impatiens

Seed and cutting-raised impatiens are important crops for the bedding plant industry, with an estimated retail value of £40m. Impatiens downy mildew has been an intermittent problem since 2003, with severe outbreaks recorded in 2008 and 2011. Research was urgently required to understand the pathogen, where it originated from, how it spread and how to control it.

Seed transmission has not been proven, so the most likely route of any outbreak is infected cutting material. Spore production in infected crops is sometimes noted on nurseries but the work also identified resting spores that permit the disease to overwinter in UK conditions on plant debris. Such spores can pose a threat to impatiens planted out in infected soil the following year.

A range of fungicide spray programmes were examined in HDC project PC 230a/b and protectant programmes were generally identified as the most effective for control. In terms of curative activity, drenches were more effective than foliar sprays. Cultural control recommendations were also provided as part of the project.

Although several effective and crop-safe products were identified, the introduction of metalaxyl-M-resistant isolates in 2011 highlighted the need to review and target fungicide programmes according to current infections.

Further HDC-funded work is due to start later this year to monitor the development of the metalaxyl-M-resistant isolate and to develop effective fungicide programmes based on a number of other active ingredients.

Dates for your diary

17 April HDC/Cut Flower Centre Conference, Springfields, Spalding.

Horticultural Development Company

For details on all HDC activity, visit

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