Impatiens downy mildew
29 August 2008
Impatiens downy mildew is a new disease that is becoming very common on busy Lizzies.
It was a new disease, discovered in 2003/2004, that has become rampant this year due to the mild, wet weather. Although commercial growers have been developing protocols for its control, slow sales at the start of the bedding plant season meant that sale plants became crowded and lanky and, combined with overhead watering, meant that it is possible that infected plants were sold to the public.
Attacks in gardens that have been reported to the RHS Advisory Department appeared to start at one spot and then spread, suggesting the airborne spread of spores from other gardens. In situations where bought plants have been infected, attacks are likely to start in several positions.
There is no remedy for gardeners for the disease, so plants will have to be destroyed, and replaced by winter bedding for example. As downy mildew spores can lurk in the soil, impatiens should not be grown in the same position in the following year. Future supplies of busy Lizzies should be disease free, but check plants before you buy them. At home ensure good garden hygiene and rotation, including destroying any infected plants. Infected plants should not be overwintered.
Defra (Department for Environment, Food and Rural Affairs) has advised commercial growers to do the following:
- Ensure that sources of propagating material, whether seed or young plants, are free of the disease.
- Adopt strict hygiene measures to prevent disease carry-over.
- Reduce humidity to discourage disease development.
- Monitor crops regularly for signs of the disease.
Symptoms of downy mildew on impatiens are available from the Defra website
If your plants have been affected report it on our My Garden forum page