EAST LANSING, Mich. — Control of downy mildew on impatiens in greenhouses continues to be an issue this year, as it has for the past several years; however, there are new treatment recommendations from a Michigan State University researcher, which should help.

By 2013, downy mildew had grown to be enough of a threat in the Detroit area that most of the big retailers were no longer selling impatiens. Retailers have instead been recommending other kinds of impatiens and alternatives such as begonias, coleus and vinca.

Professor Mary Hausbeck, an MSU researcher in the Department of Plant, Soil and Microbial Sciences, however, has developed some new recommendations that she says have proven effective. She received a farm bill grant to conduct research into downy mildew.

The recommendations are for greenhouse operators who grow impatiens for either the retail or wholesale market. “Outbreaks of the downy mildew disease on impatiens in greenhouses can quickly escalate into epidemics if not controlled,” says a memo from MSU regarding the problem.

According to the memo, impatiens can be successfully grown in landscape beds even when the planting bed has a history of impatiens infected with downy mildew. Impatiens plants must be treated with the most effective products just prior to shipping and sale.

The last application prior to planting is intended to ensure protection for an extended period once the plants are transplanted into the landscape.

The MSU research studies, which Hausbeck conducted in 2013 and 2014, showed clearly if impatiens are treated in the greenhouse with the fungicides listed in her recommendations, the risk of a downy mildew outbreak in the landscape are reduced, but not eliminated.

Hausbeck’s recommendations, which are posted online, include a number of fungicide products. They are applied over a several-week period, sometimes as a drench, sometimes as a spray, and with products used in different combinations.

She recommends fungicides including Subdue Maxx, Adorn, Compass O, Disarm, Fenstop, Heritage, Insignia and Pageant. She also recommends use of mancozeb, such as Protect DF, as well as Segway, Stature SC and Micora. Mancozeb can be added to the treatment regimen for the control of Alternaria leaf spot.

She notes in her instructions that products labeled for drench applications would include phosphorus acid-based products such as Jetphiter/Alude. She adds products mentioned in her instructions are not as such an endorsement of those products, and that brands not included shouldn’t be construed as a criticism of those brands.

“Please note the reapplication interval on the label for all products used in your downy mildew control program,” she stated. “For example, if Heritage is used as the partner drench with Adorn, skip to treatment number 4 in the ... program for your following application.”

State officials do not consider impatiens downy mildew an exotic or invasive species and, as such, do not track its spread or movement; however, the Michigan Department of Agriculture and Rural Development is paying attention to the impatiens downy mildew issue, said Jen Holton, a spokeswoman for the department. She said the disease has been in Michigan for about three years.

Greenhouse operators are encouraged to take preventive measures to protect their plants and should only purchase from a reputable source, Holton said.

Plymouth Nursery Sales Manager Missy Tuccini said her store will not sell traditional impatiens this season. Instead, it is selling a hybrid product called Bounce, which is resistant to downy mildew. It’s also selling New Guinea impatiens.

“We’re taking a wait-and-see attitude on the new treatment program,” she explained.

For a link to Hausbeck’s instruction sheet, go to a search engine online (such as Google) and use the phrase “2015 greenhouse impatiens downy mildew.” Click on the MSU memo dated Dec. 18.