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Gardening and More: A disease that is killing impatiens is likely to return

DESTRUCTIVE ORGANISMS — These Long Island impatiens looked great late last summer, before downy mildew struck them. The bottom photo was taken five weeks later, after wet weather. The impatiens have been wiped out. There is no treatment for this fungus-like disease. The best thing gardeners can do is avoid planting impatiens in the same spot next year. The organism that causes the disease stays in the soil and is carried on the wind. Photos by Margery Daughtrey.
These impatiens succumbed to a fungus-like disease.

BUFFALO — If your impatiens died this year, you might have blamed yourself for not watering them enough. The good news is, you probably did not do anything wrong.

The bad news is, your impatiens were probably killed by a fungus-like disease called downy mildew.

The disease remains in the soil, so you should plant something different in that spot, next year.

Unfortunately, there is also no treatment. “That’s the most challenging thing about it,” said Margery Daughtrey, senior extension associate at Cornell University. “There’s really nothing a home gardener can do about it. There is nothing to spray [and] nothing to buy, to counteract it.”

Daughtrey co-wrote a fact sheet called “Impatiens Downy Mildew in the Landscape,” which is available on the Cornell Cooperative Extension website for Westchester County, at counties.cce.cornell.edu/westchester/PDF/ImpatiensDM-Homeowner.pdf.

Plants will seem fine, then turn yellow, drop their leaves, lose their flowers, and even their stems.

The effects are most dramatic after rainfall, because the disease flourishes in moist conditions. Daughtrey’s before photo was taken last summer in Riverhead, Long Island and then the area was drenched in a hurricane and a tropical storm. The after photo was taken five weeks later, in mid-September, when the impatiens should have been happily blooming. Many gardeners incorrectly assumed their plants were damaged by the severe weather.

Our dry summer may have spared us, to some degree, from this problem, but the issue may get worse, as we experience wetter weather. The disease has already been reported in the Snyder and Williamsville areas of Amherst, according to Mark Yadon, vice president at Mischler’s Florist and Greenhouses in Williamsville.

There are many things that can make an impatiens plant turn yellow and have stunted growth, such as a lack of water or fertilizer. Those problems don’t usually cause the plant to drop its leaves.

If your plant has lost its leaves, you probably have the downy mildew problem. Check the undersides of the leaves. Affected plants will have a white coating that looks sugary. It is not always easy to see the coating. You may not spot it on every leaf and might need to check many leaves, before you detect it. Also note that the undersides of many impatiens’ leaves are normally a mottled purple. If you see the purple, don’t worry.

If your plants are affected, pull them up, bag them and throw them out. Do not put them in your compost!

The disease is expected to return next year.

Because this is a new disease, it is difficult to know how it will play out in coming years. It may be worse in rainy years and better in dry years. It could rage through an area for a few years, then calm down for reasons we do not understand.

The disease affects impatiens walleriana, which are standard garden impatiens, including double impatiens and mini impatiens.

The disease does not affect New Guinea impatiens, which may do well in the spot where you would ordinarily put impatiens.

Yadon said that New Guinea impatiens are more expensive to produce than standard impatiens, so gardeners who want to fill in a large area may be looking for less expensive plants.

Begonias can replace impatiens, but you will not get the same color range. You can find begonias in reds, whites and pinks, but you won’t get the salmon, purple and lavender shades.

Coleus can add color to a shady area, although it is not a flower. Other options are flowering vinca, ornamental grasses and tropical foliage plants.

No one knows why this disease, which has existed in the wild since the 1800s, is now bothering impatiens. These flowers have been around since the 1960s and are a favorite of gardeners, because they offer brightly-colored flowers for shady areas.

Now that impatiens is a less reliable plant, it may become less popular, ushering in big changes in direction for growers. Impatiens constitute 20 – 70 percent of what businesses in the bedding plant industry currently produce.

“It’s going to be devastating. Impatiens is a huge crop,” Yadon said, adding that he will probably still grow impatiens next year, but will display signs explaining the disease problem. A plant can leave the garden center perfectly healthy, then fail when it is in the garden, because the disease organism is in the soil and can be spread by the wind.

“We’ll be looking at other things to produce,” Yadon said. “We have to figure out something else to do and make it affordable to homeowners.”

Connie Oswald Stofko is publisher of Buffalo-NiagaraGardening.com, the online gardening magazine for Western New York. Email Connie@BuffaloNiagaraGardening.com.

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