Downy mildew on Impatiens walleriana has been confirmed in more than 30 states, primarily in the eastern half of the United States. In 2012, the disease first started to be seen in Florida and then made appearances up the East Coast and in the Midwest during the spring and early summer. Landscapes in drier areas in the East were affected by the disease in late summer. Impatiens downy mildew also appeared in Texas, Washington, Oregon and the Gulf Coast states in 2012.
“The disease was identified in only 13 states in 2011 and in 33 states in 2012,” says Margery Daughtrey, senior extension associate at Cornell University’s Long Island Horticultural Research and Extension Center in Riverhead, N.Y. “Even though a state was noted as having the disease, that doesn’t mean the entire state was affected. It means that a particular state had a case reported. It could have just been one case — and it might have been seen in either a greenhouse or landscape.”
Daughtrey said that the disease has also been identified in the Canadian provinces of Quebec and Ontario.
“Growers in New York are very sensitized to the problems and concerns associated with impatiens downy mildew,” she says. “There were obvious problems with the disease in the greater New York City area last year. Previously it was thought of as a fall disease. Last year, it showed up in early June. After that experience everyone is quite shocked because it appeared so early in the season.”
Daughtrey identified the disease in landscape plantings in the fall of 2011 on Long Island.
“I was surprised that there were no calls to my office or to Cooperative Extension in 2011 regarding landscape problems,” she says. “I think most people thought it was early frost damage or injury from a late-season hurricane and tropical storm that occurred here. Nobody looked for any other explanation as to why the impatiens were losing their leaves, which began to occur in mid-September.”
Understanding The Disease
Daughtrey says a number of meetings were held in 2012 on Long Island to educate growers about downy mildew and what they can do to keep the disease out of their greenhouses.
“The growers are well aware of the disease and its potential, and they are making plans for 2013,” she says. “This is an area where a lot of ornamental product is produced and consumed. And a huge percentage of the flowering bedding plant usage is impatiens. This has made us more aware of the fact that we are at the center of this disease problem and its solutions.
“At the same time, New York growers want everyone to know and understand that this is an industry-wide and nationwide problem. They don’t want their customers to think that there is something wrong with them as suppliers. It is in their best interest that we help everyone understand that the problem is a disease and it is something that we have to work together to try and solve.”
Controlling The Disease
Many growers began using a preventive spray program last spring, and Daughtrey worked with Michigan State University Plant Pathologist Mary Hausbeck last year to devise a chemical control program for growers.
“It was the best thing we could come up with using available chemical controls at the time,” Daughtrey says. “Since then we haven’t found anything that will work better. The program consists of rotations of active ingredients that show efficacy against downy mildew. The program is weighted, so as plant material comes into and leaves the greenhouse, it calls for applications of the most effective systemic materials. This way growers stop anything that might have inadvertently been brought in on plant material. Also, when the finished plants are shipped, they are being sent out with at least several weeks of continued control against the disease.”
Chemical control programs for the disease have also been released by Ball Horticultural Co. and Syngenta.
“Exact recipes needn’t be followed,” Daughtrey says. “There are multiple strobilurin fungicides that are effective, so those could create an identical impact, regardless of the chemical manufacturer. All of the control programs that I have looked at make sense to me. Materials chosen should be effective against the disease and rotated appropriately to delay resistance development.”
Growers Respond By Producing Less
Bryan Young, chief administrative officer at Young’s Plant Farm in Auburn, Ala., is well aware of the downy mildew problem that has occurred in landscape plantings, especially in Florida. His company ships bedding plants to retailers, primarily big box stores, in the southeastern United States.
“Our market includes Alabama, Florida, Georgia, Louisiana, Mississippi and Tennessee,” Young says. “We have not had any major issues so far, unlike what occurred in south Florida, where retailers didn’t want impatiens because of the disease. Retailers and consumers in other areas are not as aware of the disease as they are in south Florida. A lot of the cases we heard about last spring were along the coastal areas of Louisiana. We also heard of some cases in northern Alabama.”
Like growers in the Northeast, Young said his company made changes to its fungicide application program in 2011 to ensure the disease did not become a problem.
“We have not seen any cases of downy mildew in our greenhouses so far,” he says. “We plan to continue this spray program during the upcoming spring. Our growers looked at the control programs developed by Ball and Syngenta to decide what we were going to do. We have always had a preventive program for downy mildew in place, but we have looked at the information that has been made available, and we’re trying to make sure we follow those recommendations.”
One of the biggest changes Young’s will be making is the reduction in seed impatiens it will produce for spring 2013.
“We have reduced our Impatiens walleriana production by about 15 to 20 percent,” Young says. “We have added more New Guinea impatiens and SunPatiens. We did not roll all of that 15 to 20 percent reduction into New Guineas and SunPatiens, because those are premium items. A greater amount of that production will be other basic items including begonias and shade coleus, which are grown in flats and packs.”
Another thing that Young plans to do is evaluate the disease situation on a weekly basis.
“We currently have about an eight- to nine-week production schedule from seed to finish container,” he says. “If the disease starts to show up early, we will shut down impatiens production and focus on alternative shade crops. If things go well and the disease doesn’t become an issue, then we probably won’t make any further reductions in impatiens production. We will be proactive in our production planning to make any necessary adjustments.”
Al Lively, head finish grower at Wenke Greenhouses in Kalamazoo, Mich., says some landscapers in the state have reported cases of the disease.
“We have seen a drop in sales of Impatiens walleriana,” Lively says. “We will be prepared to offer something different in case the disease does become a problem.”
He says the company is leaning toward growing more of the seed-produced Divine New Guinea impatiens.
“Some of our customers are starting to look at replacing garden impatiens with other plants, including begonias, New Guinea impatiens that can take the shade and even SunPatiens,” Lively says.
The company has also increased its use of fungicides to prevent the disease.
“We spent more money on fungicides last year compared to what we have spent in the past,” he says. “We have a precautionary program specifically for impatiens downy mildew. We make spray applications of different chemicals every seven days. We want to make sure we keep it under control.”
Lively says Mary Hausbeck at Michigan State University, along with Ball Horticultural Co. and Syngenta, have provided recommendations and feedback regarding the disease.
“Mary Hausbeck had a meeting with the growers here in Kalamazoo to go over things,” Lively says. “She spent more than three hours with us discussing the disease and answering our questions.”
Even though Lively expects overall sales of I. walleriana to drop in 2013, he said his company is trying to avoid scaring anyone away from not ordering impatiens.
“I think most garden centers are going ahead and placing their orders based on their sales from last year,” he says. “If they didn’t have any problems with the disease, I expect that they will re-order impatiens this year.”
Educating End Consumers
Although many growers have become aware of the disease, Daughtrey says more consumer education needs to be done.
“The gardeners haven’t gotten it yet,” she says. “Their education is lagging behind that of the growers. There is still a lot of ignorance among the public about the disease. Growers in areas where the disease has occurred and who supply independent garden centers are by and large cutting back. The amount varies with each grower.”
For those growers who supply landscapers who were impacted by the disease, Daughtrey says I. walleriana sales will probably be non-existent.
“Landscapers in the New York metropolitan area are well aware of the disease,” she says. “They are not interested in taking on potentially large losses by planting masses of impatiens that may not last more than a month. Fortunately, the landscapers are still interested in planting flowers. The growers who have good relationships with their customers are working with them to steer them to other crops that can replace Impatiens walleriana.”
Daughtrey said that growers and retailers are going to have to repeatedly stress to the public that New Guinea impatiens and SunPatiens are resistant to the disease.
“Garden center operators don’t want to have these long-winded discussions with their customers this spring,” she says. “They want to be able to educate their customers with signage and not turn people off.”
Young says his company is planning to use plant tags with New Guinea impatiens and SunPatiens that advise consumers that these impatiens are disease resistant.
“We are trying to educate average consumers so that they don’t start to think that all impatiens are susceptible to downy mildew,” he says. “We have to make them aware that not all impatiens get the disease.
“The concern is how to fill the gap for those consumers who normally buy garden impatiens so they continue to buy either New Guinea impatiens, SunPatiens or an alternative plant and not give up on gardening. If consumers aren’t buying impatiens, we want them to be happy with something else and not leave the store without a plant. Some people will still want an impatiens and be willing to pay a higher price for SunPatiens or New Guineas. Some are going to be shopping for a certain price point for a shade plant. That is why we have added the shade coleus and begonias for those consumers shopping by price point.”