What is Happening with Garden Impatiens in 2013?

Garden impatiens (Impatiens walleriana) may not be a cut flower but many cut flower growers sell them at farm markets. They are relatively easy to propagate, making them ideal for spring sales. It’s hard to beat their diversity of flower colors, shapes and textures. Garden impatiens have represented over 25% of spring sales of plant materials from commercial greenhouses, and have dominated landscapes for years.

Unfortunately, a new disease problem in the impatiens world will impact your choice of annual plants in 2013.

For years this group of plants was considered pretty disease resistant and fairly durable. That is, until 2012 when downy mildew devastated garden impatiens on the East Coast. Downy mildew had been reported in greenhouses but it was not highlighted as a major problem in landscapes until the last couple of years. This strain of downy mildew has the potential to overwinter outdoors in landscapes.

If your plantings were infected in 2012, you may have problems if you use impatiens in the same beds this year.

Many defoliated garden impatiens samples were submitted to the University Extension Plant Diagnostic clinic in 2012. The most frequent question was “Why did these plants drop all their foliage?” Pictures sent to us at CMREC showed impatiens looking like green sticks with naked stems sticking straight up. If you had infected plants, all plant material should have been removed from the area, but this is a nearly impossible job when most of the foliage dropped off into the mulch where the fungus can overwinter.

In Florida and Georgia, where the bedding plant season is already in full swing, they are seeing downy mildew showing up in many landscapes. The spores can be blown on the winds and as we start receiving trade winds from the south we may well see spores blown into our area.

At the 2013 MANTS show in Baltimore, a special meeting was held by the Maryland Greenhouse Growers, Syngenta Company and Ball Company. The purpose was to discuss the impact of the destructive downy mildew that inflicted damage in multiple states, including Maryland, in 2012 and what the horticultural industry should be doing in 2013.

Plants are Affected Quickly

First off, this is not the regular, run-of-the-mill downy mildew. This disease, in the right weather conditions, infects a plant and forms spore within 5 days, sickening the plant and often resulting in foliage drop, leaving stems looking like bizarre, unattractive,  art deco pieces. While there have been sporadic reports of this disease in production greenhouses in the United States since 2004, widespread regional outbreaks of impatiens downy mildew were observed for the first time in North American landscapes in 2011 in several states.  Impatiens downy mildew was confirmed in an increased number of the states in 2012. The disease was the “hot topic” at winter meetings for greenhouse plant suppliers and greenhouse growers. All varieties and intraspecific hybrids of Impatiens walleriana are susceptible to impatiens downy mildew, including both vegetative- and seed-produced I. walleriana. There are no noticeable differences in susceptibility among varieties. So selecting a resistant variety is not an option at this point.

What to Do In 2013?

The majority of the greenhouse growers attending the meeting at MANTS decided to not grow garden impatiens, or to greatly reduce their inventories in 2013 and concentrate on providing other plants that perform well in shaded situations.

One alternative is fibrous begonia. Although fibrous begonias do not have the spreading habit like garden impatiens, the foliage colors are great with white, pink and red flowers available. The prices tend to be similar to garden impatiens so if your margin line is tight this would be a good choice.

Dragon wing begonia is a full plant with great foliage and fantastic flower display that is an excellent substitute for garden impatiens. The Whooper series has bronze foliage and bright red flowers. Tuberous begonias are another choice and do well in partial shade.

This would be a good year to get creative with coleus. With coleus you are growing the plants for the foliage and there are a wide range of foliage colors available. ‘Trusty Rusty’ has excellent yellow-gold foliage, and ‘Redhead” and ‘Lava Rose’ are also colorful.

Don’t discount caladiums. They do not do well with the cold in spring but take off in summer. The hotter the summer the better caladiums perform. The foliage colors are fantastic with strong reds, variegated red, pinks, and white variations.

One interesting impatiens with resistance to downy mildew is Impatiens repens. The foliage does not look like a garden impatiens and the yellow flower is shaped like an Indian peace pipe. It flowers well in spring but slows down in the heat of the summer. The foliage is attractive, plants thrive in heavy shade, and they’re easy to propagate.

Downy mildew on garden impatiens showed up in Florida and California in early 2013. The greenhouse growers and garden center group attending the meeting asked us to get the word out on this disease, and explain why garden impatiens are not a good choice for 2013. Spend a little time exploring alternative plant material.

Karen Rane

Extension Pathologist and Director

Karen Rane is Extension Pathologist and Director of the Plant Diagnostic Clinic, University of Maryland Extension. Contact her at [email protected].

Stanton Gill

Extension Specialist

Stanton Gill is an extension specialist (professor-ranked principal agent) in IPM and entomology with the University of Maryland Extension, based at the Central Maryland Research and Education Center in Ellicott City. He is also a professor in the Landscape Technology Program at the Germantown Campus of Montgomery College. Contact him at [email protected]

Photography by David Clement