Impatiens are easy flowers to grow.
They thrive in shade and come in just about every color imaginable.
But gardeners are being cautioned against planting impatiens this spring, because the plants are being infected with downy mildew, a fungus-like disease that kills impatiens.
No one is sure where the disease originated, said Gary Moorman, plant pathologist with Penn State.
"The actual organism has been known for a long, long time but why it started showing up on garden impatiens, we really don't know," Moorman said.
Downy mildew began showing up in impatiens in 2011, and Pennsylvania began to see a lot of it in 2012, he said.
"There was so much of it last year that the organism will survive in the soil, so if impatiens are planted again this year they will become infected," Moorman said.
The disease spreads through the air and soil, and it kills impatiens, causing them to shrivel up in a matter of days or weeks, said Moorman.
The exceptions: All of the common garden impatiens are susceptible, but the disease does not affect New Guinea impatiens.
SunPatiens, a new hybrid, are also not affected by downy mildew, but the New Guinea impatiens and sunPatiens are not as tolerant of deep shade as the garden impatiens people favor, said Moorman.
Gardeners need to look for alternatives, such as begonias, if they want to protect their gardens - but even then the disease can blow in from a neighboring property, Moorman said.
The wet weather and early spring in 2012 increased the spread of downy mildew, but if spring is warm and dry this year the disease might clear up sooner, he said.
Otherwise it could linger in the area for a long time, because the infecting spores remain in the soil, Moorman said.
Dave Miller, owner of Miller's Plant Farm in York Township, said last year his farm grew more than 2,000 flats of impatiens, but this year they will only grow about 1,000. [mfr: why? Because they think there will be less demand?: ]
"It is one of the top selling bedding plant flowers," Miller said.
Miller said the problem is not everywhere, and he has talked to some people in York County who have still been able to grow the impatiens without any problems yet.
"We have controls in the greenhouse so that we can send out clean plants," he said.
The weather will be the main factor in determining whether the disease continues to spread this year or if it begins to disappear, said Miller.
Downy mildew affects a lot of vegetables, but each strain is different and this particular strain only affects impatiens, Miller said.
The most important thing for gardeners to do is to not plant any impatiens in the same spot they were planted last year, Miller said.
Wax begonias and coleus are good substitutes that do well in the shade.
New Guinea impatiens are similar in looks, but more expensive and do not do as well in the shade, he said.
"What I am looking forward to - and I'm sure the seed companies are scrambling to find - is a resistant strain," Miller said. "It is a shame to lose such a popular flower, with the wide range of colors they can offer."
The Associated Press contributed to this report. Reach staff writer Chelsea Shank at 505-5432 or firstname.lastname@example.org