When nurseries voluntarily stop selling a popular plant something must be up. Well, the plague of downy mildew wiping out Impatiens in Britain has led four of the biggest producers to say that they just won’t supply vegetatively propagated (cutting-raised) varieties like 'Fiesta Sparkler Orange (above, click to enlarge) at all. And some nurseries are cutting back their production of seed-raised impatiens by as much as 60%.

Impatiens downy mildew is caused by a fungus called Plasmopara obducens. The leaves turn yellow, drop off and rot rapidly; the flowers drop off too. Plants end up as cluster of pale stems and not much else. The disease thrives in wet summers. It only seems to attack the most widely grown Impatiens species, I. walleriana.

First seen in Britain in 2003, last year it swept the country killing plants in gardens, public displays, and in nurseries before the plants even went in the ground. New resistance to the one effective fungicide is blamed.

In North America the disease was reported this year from coastal southern California; northeast Illinois; northern Indiana; Cape Cod, Massachusetts; and Long Island and upstate New York.

Vegetatively propagated (cutting-raised) impatiens are more likely to be hit because plants are usually sold in flower as individual specimens so are on the nursery amongst thousands of others for longer. And mother plants from which cuttings are taken are a nightmare to keep clean and healthy. The growth of many varieties is also very tight so each plant creates its own little high-humidity microclimate. And in the moist conditions needed for rapid growth on the nursery the fungus can grow quickly too. And if your fungicide is useless…Find out more on the Royal Horticultural Society’s website.

Seed-raised types are on the nursery for a shorter time and sold as much smaller plants and for, gardeners, one option is to grow from seed or from bought in seedlings. But plant in a new site or in fresh container compost each year; spores can overwinter in the soil and infect plants the following year.

But, looking ahead, the problem may not be with us for ever. It’s thought that adding fungicide to compost may give protection and decades of experience in developing resistance to a similar disease in lettuce is being brought to bear.

Finally, some two sided news. Because this form of downy mildew only attacks I. walleriana, in favoured areas we can plant New Guinea impatiens instead, although these are often more expensive. It also means that early optimism that the disease would wipe out invasive Impatiens glandulifera, Himalayan balsam, is unfounded.

Best option? Grow begonias or fuchsias instead.