Impatiens fungus threatens popular, colorful plant
By Bob Karlovits
Published: Friday, May 3, 2013, 8:40 p.m.
An airborne fungus has taken root in this area to create a threat for one of the most popular landscape-decorating plants.
“It doesn't look good for little impatiens,” says Linda Hyatt, horticulture assistant at the Westmoreland County extension service of Penn State University.
Linda Ban from Kiski Garden Center, near Leechburg, agrees.
“You can't fix the soil,” she says.
The problem is a fungus that causes impatiens downy mildew, which makes leaves turn yellow and drop and eventually causes the plants to collapse. It was first seen in the United Kingdom in 2003-04, and then in this nation in 2010, becoming major threat in 2012.
Because of the spread of the fungus, Ban says, the Kiski Garden Center has reduced “by thousands” the number of impatiens planted. It uses only the soil known to be unaffected.
Dan Higgins from Michael Bros. Nursery in West Deer says, “it's a major, major plant because people love them.”
The most popular variety of the plant — Impatiens walleriana — is particularly susceptible, says Gary Moorman, professor of plant pathology at Penn State's Centre County campus. But he says the fungus also is infecting jewelweed (Impatiens capensis), the variety that grows wild in Pennsylvania.
Perhaps the biggest issue is the plants then infect the soil, giving the fungus a home.
“My guess is that this will not go away anytime soon,” Moorman says.
He, Ban and Hyatt suggest choosing other plants. They say New Guinea impatiens and SunPatiens, which grows in sun and shade, are not affected, along with coleus and begonia. Ban also recommend torenia because of its ability to work well in partial shade.
But most plant professionals realize the popularity of impatiens and know a warning is called for.
“If you use them, be aware you might lose them,” Moorman says.
Some growers are not entirely pessimistic.
Higgins says the threat “is not going to last forever” and believes spraying with a good fungicide such as Daconil would be effective.
But he also says it is wise to “reduce your risk” by using another form of plant.
“I'm not a pathologist,” he says. “My job is to help people make their property look better.”
Moorman, however, does not think spraying will help because once the spore is on the leaf, the damage is done.
“The chance of controlling a fungus with spraying is not too good,” he says.
Joan Brenckle from Brenckle's Farms and Greenhouses in Reserve says she is comfortable with the plants she has produced, because they all are grown in greenhouses and safe from the spores.
Of course, once removed from the house, they can become victims to fungus in the air or soil.
Bob Karlovits is a staff writer for Trib Total Media. He can be reached at email@example.com or 412-320-7852.
Question: What is impatiens downy mildew?
Answer: Impatiens downy mildew is the common name for a disease caused by a fungus-like organism called Plasmopara obducens. It can infect and kill bedding impatiens. The disease can be spread by wind or water, and it can also live in the soil where infected plants have grown. It first shows up as a downy white growth on the underside of the leaves and can quickly cause the plant to turn yellow, lose its leaves and collapse.
Q: I grow cucumbers in my garden. Could my impatiens give them downy mildew?
A: No. Downy mildew is a common name given to a number of diseases that affect different plants. The various types of downy mildew are caused by different organisms. The organism that causes impatiens downy mildew infects only certain kinds of impatiens.
Q: Is there a way to tell whether my impatiens will get the disease?
A: You should look under the leaves for white growth before you buy or plant impatiens, but even if the plant looks clean, that's no guarantee it's unaffected. The organism can be present in a plant long before the first signs of disease show up. The pathogen needs moist conditions to flourish, so, a plant that seemed perfectly healthy might suddenly become sickly during a rainy spell.
Q: What can I do to prevent the disease?
A: Some fungicides are available to growers and landscapers that can prevent downy mildew. Unfortunately, the fungicides that researchers consider most effective are not available to home gardeners.
Q: I heard it's OK to plant impatiens in containers but not in the ground. Is that true?
A: Impatiens planted in the soil where infected plants have grown are at particular risk, because the disease-causing organism can live in the soil for years. But no bedding impatiens are completely safe. Disease spores can be carried by wind or splashing water and can spread to plants in the ground, in pots or in hanging baskets.
Q: What should I do if one of my plants gets the disease?
A: Remove the plant immediately and throw it away in a closed plastic bag. Avoid planting impatiens in that site for at least a few years. Don't yank a plant just because it looks sickly, however. Symptoms such as yellowing and leaf drop can be caused by other factors that are easily remedied, such as too much or too little water. If you suspect infection, look under the leaves for the telltale white growth.
Q: Can I put diseased plants in my compost pile?
A: That's not a good idea. Most backyard compost piles don't get hot enough to kill the pathogen. If you do compost the plants, don't use the compost on or near healthy impatiens.
Q: I really love impatiens. Should I avoid planting them?
A: Only you can make that call. Just recognize that you're taking a risk of losing plants. You'd be wise to keep a close eye on your plants for signs of the disease. Especially if you're planting impatiens on a large scale, you might also want to have a landscaper treat your plants with fungicide on a regular basis.
Sources: Jim Chatfield, Ohio State University Extension; Michigan State University Extension; American Floral Endowment; Cornell University Cooperative Extension; University of Massachusetts Extension
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