The shade garden’s best friend, impatiens walleriana, is at risk from a deadly spore that wiped out some area beds last summer but left others unscathed.
Experts expect the aggressive mold, impatiens downy mildew, to be ruthless again this summer, but whether, where, and when it will strike is up for grabs.
“Everybody agrees we should educate the public. From an ethical standpoint, people should know what’s going on,” said Walter Krueger, owner of Lakewood Greenhouse in Northwood and a member of Maumee Valley Growers. Last fall, he decided against planting flats of impatiens for 2013.
“It’s pretty much a death sentence, as far as I’m concerned,” he said. “Nobody can afford to give customers a money-back guarantee. And we don’t want unhappy customers.”
But when it’s Mother Nature’s game, outcomes can’t always be predicted. Across the Maumee River, longtime Hill Avenue grower Tom Strain made a different call. He planted 14,000 flats of impatiens (down from 20,000 in 2012) and took pains to ensure they’re disease-free by treating them with a fungicide every seven to 10 days and regularly inspecting the undersides of leaves and the roots for any trace of the mildew. A state inspector spent hours walking up and down the aisles of the greenhouses. But once flats of impatiens exit the Strain’s controlled environment, they’ll be susceptible to the vagaries of wind and water.
TIPS FOR GARDENERS
■ If you buy impatiens, purchase them from a reputable grower. Look on the underside of leaves and at roots. Plants should be vigorous and green with no yellowing or yellow dots on stems or leaves. Ask what measures the grower took to protect them from the impatiens downy mildew mold.
■ Do not plant impatiens if your 2012 impatiens died from downy mildew. If you discover impatiens downy mildew on your plants, carefully bag up all the debris, seal the bag, and dispose in the trash. Do not put in compost.
■ Other shade-tolerant plants include New Guinea impatiens, sunpatiens, fibrous begonias, dragonfly begonias, coleus, lobelia, torenia, bedding vinca, polka dot plant, and some salvias.
■ For more information: The American Floral Endowment’s Web site, www.endowment.org/impatiens.
The most popular impatiens sold, impatiens walleriana includes varieties such as double impatiens, fusions, and some butterfly impatiens. Impatiens were estimated to be a $105 million-a-year crop for American growers in 2007 (the most recent year for which a figure is available), said Mary Hausbeck, a plant pathology professor at Michigan State University Extension. She enjoyed beautiful impatiens at her Lansing-area garden last year and intends to replant this year.
“People should always take a good look at the health of the plant they’re buying,” said Ms. Hausbeck, who’s part of a multi-university team studying downy mildew. Stems and leaves should be solid green and sturdy, roots should be vigorous, and the plants should be a good size. She recommends buying from a reputable grower.
Impatiens downy mildew (Plasmopara obducens), thrives in cool (about 59 to 73 degrees), damp conditions and appears as a white, downy coating on the undersides of leaves. It’s easy to miss but by the time it appears, it’s too late to cure. It was seen in Michigan in 2004, said Ms. Hausbeck, but seemed to go away. It is not the same variety of downy mildew that damages other plants such as cucumbers or sunflowers.
In Florida, it was identified it in 2011, and by 2012, it was taking out impatiens in dozens of states.
Cedar Point planted 100 to 125 flats last spring and lost them all by midsummer, said Martha Beverick, landscape supervisor at the amusement park. Replacing them were Big Red begonias, which did so well in shade, sun, and hanging baskets that the park will use them again.
Last summer’s warm, dry weather in our area kept the mold latent in many places until mid-August when two key factors woke it up: overnight temperatures cooled and dew became heavier.
Tom Creque of Creque’s Greenhouse in Sylvania was disheartened so see the devastation at beds he’d put in at Lourdes University and two golf courses. This year, he grew a small number for use in baskets, which seemed to have more resistance than those flowers in the ground, he said.
“The disease is here but we’ve taken measures to protect our plants,” said Mr. Creque, adding that there is not yet a fungicide available to consumers to protect against the mold in their gardens. Having spent 25 years building a strong reputation, his family didn’t want to risk selling sick plants.
“Gardening is tough enough as it is. We want to eliminate the chances of you failing,” he said. He’ll lead a free program for customers at 7 p.m. May 2 at the greenhouse, 9700 Sylvania Ave., about downy mildew and alternatives to impatiens, similar to one he gave in March.
After planting more than 100 flats of impatiens a year for more than a decade, Bob Lubell can’t put them in this year because the mold killed thousands of flowers on his three Sylvania acres in August. It’s almost certainly lurking in his soil, where it may survive for several years.
“This year I don’t know what I’m going to do,” said Mr. Lubell, a photographer who employs his beautiful landscape as a backdrop for photo shoots. Consumers should expect to see informational signs in stores about impatiens downy mildew and other plants that can tolerate shade.
Contact Tahree Lane at: firstname.lastname@example.org or 419-724-6075.