Connolly: Alternatives for a colorful garden in a post-impatiens world
When Tina Bemis heard about impatiens' downy mildew early in 2012, she didn't press the panic button. She and her husband operate Bemis Farms Nursery in Spencer, Mass., and the annual impatiens sale was their biggest event of the year. "We sold over 1,800 flats each year," she said. "We'd been running the sale for 13 years."
But by late June 2012, Bemis said, "People were asking me, 'Why did my impatiens turn grey and die?'"
That's when she knew she'd met the enemy - a fast-acting, fungus-like, tongue-twister pathogen called Plasmopara obducens. This bad actor goes after several impatiens species, even our native impatiens, the jewelweeds.
"Once you notice the symptoms in your garden, the plants are dead in a matter of days," said Bemis. There is no effective cure at this time, she added.
Now, as her nursery prepares for a post-impatiens world, she is speaking to groups about alternative plants and has renamed the annual sale, "Begonias and Buddies." For comparable cost-effectiveness, she places coleus, begonias and nicotiana at the head of her list for bright garden colors. If you are willing to pay a little more, New Guinea impatiens and their relatives, the Sunpatiens, are resistant to the disease.
For now, most horticulturalists agree with Bemis, who said, "It's best not to grow impatiens - they simply provide a home for the nasty pathogen." And then she quipped, "Impatiens - who needed them anyway?"
Bob Heffernan, executive director of the Connecticut Nursery and Landscape Association, said that greenhouse production is way down. "Growers really can't take the chance," he said. In the meantime, he said plant breeders are working on disease-resistant impatiens and they may be safe to plant again sometime in the future.
So this year, think coleus, think begonias, and while you're at it, think about a couple other garden problems you can dodge with a little planning: boxwood blight and basil downy mildew.
Boxwood blight (and pachysandra, too)
Seeing spots on your boxwood leaves? It's not your vision; it's probably boxwood blight. After spots appear, the leaves fall and blackened stems remain. It's been found on pachysandra as well. According to the Connecticut Agricultural Experiment Station (CAES) in New Haven, the pachysandra infections mostly show up where boxwood blight is already underway. The pachysandra version first appears as dark circles with yellow haloes on pachysandra leaves.
"I don't advocate complete abandonment of boxwood," said CAES spokesman Robert Durgy. The disease is not widespread enough in the environment and nurseries are very aware of the problem, he said.
"They're doing everything they can to not sell infected plant material."
If you want to replace dead boxwoods, talk with your nursery about the best way to get and maintain new plants.
Another strategy is to consider inkberry (Ilex glabra). It's a native plant with a very similar appearance. It's also a great plant for local pollinators and birds.
If pesto pizza is your thing, read on. Basil downy mildew is here.
According to Joan Allen, assistant extension educator at the University of Connecticut, "Very few varieties of sweet basil, Ocimum basilicum, are resistant." The disease turns leaves yellow between the veins, and then the leaves blacken.
What's a pizza lover to do? Enter Plan B. "There are lemon and lime culinary varieties (Ocimum citriodorum) with pretty decent downy mildew resistance," said Allen. These include Lemon Standard, Mrs. Burn's Lemon, Lemona, and Lime basil. She added that some of these may develop some yellow spots on the leaves but not have too much injury.
The most resistant basils are Spice and Blue Spice (O. basilicum crosses) she said.
As for the ornamental basils, some have the color and beauty of coleus and may even help make up for the loss of impatiens. Allen suggests cinnamon basil, Amethyst Imp, Sweet Aden, Red Rubin and red basil as varieties that are resistant to basil downy mildew.
Information on all these diseases is available from the UConn Home & Garden Center website at www.ladybug.uconn.edu/ or by calling (877) 486-6271) or from the Connecticut Agricultural Experiment Station, www.ct.gov/caes or (203) 974-8500.
Forewarned is forearmed. In the garden, sometimes a good defense is the best offense
KATHY CONNOLLY IS A GARDEN WRITER, LANDSCAPE DESIGNER AND SPEAKER. HER EMAIL IS KATHY@SPEAKINGOFLANDSCAPES.COM. FIND HER BLOG AND PRESENTATION SCHEDULE AT WWW.SPEAKINGOFLANDSCAPES.COM.
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