After 10 years of limited availability and drastically reduced popularity, busy Lizzies have seen something of a renaissance in the last couple of seasons but now it seems that they could again be dying as a result of a very particular fungal disease. The sudden collapse of otherwise healthy plants is usually the first sign that something’s wrong.
First appearing in the UK in the early part of the century, impatiens downy mildew swept through nurseries and gardens so that by 2011 when a huge outbreak occurred, busy Lizzies seemed no longer viable for summer bedding and container planting. After lots of breeding to produce disease-resistant varieties and a decline in the fungus due to the plants not being widely grown, things seemed to be improving for the common bedding busy Lizzie, Imaptiens walleriana and its varieties, the only species seemingly affected with the problem.
But this summer’s moist conditions and intermittent warmth have encouraged local flare ups of the disease and a friend in the south of Dorset got in touch last week to say that plants were collapsing and dying again. It seems that the newer, resistant varieties are not totally immune from infection.
What does impatiens downy mildew look like
The mildew itself appears as a fine, white felt on the backs of the leaves and this may not be noticed at first. Leaves turn yellow and start to fall from plants, together with the flowers and the whole stem structure can start to collapse – particularly during periods of strong wind and heavy rain. The infection spreads very quickly to cover the entire plant. Severely affected plants may be left as bare stems.
Plants can be infected for some time before obvious symptoms are visible – even in the form of the white, felt-like growth.
How to prevent Busy Lizzie wilt
There is nothing that can be done to overcome an attack of this fungal disease. Growing plants in well-ventilated, open conditions can offer some limit to its spread, but in damp summers this appears not to help. There are no fungicides available for its treatment.
It is important that the plants are removed immediate and burnt or buried deeply – a minimum of 60cm deep. Do not put the material on your domestic compost heap or put out for green waste collection if at all possible. Spores of the fungus can last for a number of years in soil and compost, so it is best not to grow busy Lizzies in the same place in the following season. Spores spread on the wind and in rain splash so may infect from neighbouring gardens where infections occur.
‘New Guinea’ forms of busy Lizzie are not prone to the disease, probably due to their different leaf texture or some in-built genetic resistance. Other commonly used summer bedding and container plants are not affected either.