Mildew thins Lizzy.
IMPATIENS walleriana, commonly known as Busy Lizzy, has in the last 30 years come from nowhere to be the nation''s favourite summer bedding plant because of its outstanding ability to flower continuously throughout the summer without the need for deadheading. However its popularity is now threatened by a menacing new disease, downy mildew (plasmopara abducens).
The disease is specific to impatiens and cannot spread to other bedding plants.The disesase is most prevalent during periods of low temperatures, high humidity and rainfall and is exacerbated by low nutrient levels in the compost.
Early signs of infection include leaf yellowing or mottling, and shedding of leaves and flowers. As the disease develops plants become stunted and white spores appear on the underside of the leaves. In severe infections the plant is reduced to a skeleton of bare branches, or even death of the plant. If discovered plants should be bagged up and disposed of, or ideally burnt. Do not compost them, and thoroughly clean infected pots before replanting. Avoid replanting the same piece of ground with impatiens for at least 12 months.
There are no effective fungicides available to amateur gardeners to control the disease, but keeping the foliage as dry as possible, by watering the soil, not the foliage, will provide less favourable conditions for the production and dispersal of spores.
In future, space plants out well in the border and consider planting alternately with another species.
Interestingly the larger flowered New Guinea impatiens is not affected by this disease and could be used as an alternative, although it is a more expensive option.