7 Tips For Protecting Impatiens From Downy Mildew

Last year’s outbreak of downy mildew in Europe virtually destroyed the crop and caused garden centers and mail-order catalogs to discontinue stocking it in favor of less problematic crops. A nationwide outbreak here in the United States is probably a stretch because regions experience vastly different environmental conditions. Still, downy mildew was spotted on impatiens on both coasts last year, so growers should be on high alert for the disease.

“Impatiens grown in many areas of the United States may never be infected with downy mildew,” says Dr. Colleen Warfield, Plant Pathologist for Ball Horticultural Company. “Other areas may only see this disease sporadically. But if growers and landscapers are not aware of this disease and how to manage it, it certainly has the potential to develop into a far more devastating disease.”

Speedling’s Mike Friddle, who was named Greenhouse Grower’s 2011 Head Grower of the Year, says he is confident the industry can stay ahead of the downy mildew issue with sound, preventative practices and open communication with suppliers and plant pathologists.

“By working together with a common goal to protect this crop, there is good reason to believe we can grow it, even if there are isolated future cases,” Friddle says.

So how can you protect impatiens in your greenhouse? Here are seven steps to follow.

1. Know The Cause

Downy mildew can be introduced into growing facilities either on infected material via plugs, cuttings or plants, or by wind-dispersed aerial spores from infected plants in the landscape, says Warfield.

“If growers are propagating or finishing plant material in a region where Impatiens walleriana are being simultaneously grown in the landscape, these growers have a much higher risk of their crop becoming infected with impatiens downy mildew due to airborne spores,” she says. “Growers in these regions will need to be especially vigilant in scouting for early disease symptoms, protecting their crops preventively and carefully monitoring the environment to minimize both humidity and extended periods of leaf wetness.”

2. Start With Clean Plants

For growers at every level, purchasing disease-free plant material is a critical step toward avoiding disease issues. Because there is no evidence for seed transmission of downy mildew, impatiens grown from seed are initially free of the disease, according to Warfield.

Vegetative impatiens grown from clean stock, however, can still have a latent infection. She recommends growers separate seed- and vegetative-grown impatiens, as well as material from various sources, to reduce cross contamination.

Finished growers should always order their young plants from suppliers who are known for clean production and following manufacturers’ production recommendations, Friddle says.

“Growers must isolate the plug trays from other Impatiens walleriana and Impatiens pallida and capensis, all of which can host the disease,” Friddle says. “Then, inspect all trays prior to transplant.”

3. Scout For Symptoms

Growers must implement a strict scouting program and educate employees to recognize pathogen symptoms. Young plants should be carefully inspected for signs and symptoms of downy mildew upon arrival. The pathogen is systemic, so once a plant is infected, any potential management practices are ineffective. Plants showing symptoms must be diagnosed, removed and destroyed immediately.

“Carefully scout cutting-raised material for symptoms, especially during the first 11 to 14 days when plants are likely to have been placed under a mist system,” Warfield says. “It’s very important to look at the underside of the leaves for the characteristic white, downy-like growth or sporulation, keeping in mind it may be very sparse and barely visible without a hand lens. Use other visual cues such as leaf stippling, chlorosis and downward curling of the leaf margin to detect potentially infected plants.”

4. Destroy Infected Plants Immediately

Once symptoms have been identified, one of the most important sanitation measures is to dispose of infected plants.

“If an infected, sporulating plant is discovered in the growing facility, place the plant in a bag and seal it before moving it out of the greenhouse to minimize the spread of spores,” Warfield says. “These airborne spores are rather short-lived and won’t survive for long on dry, inanimate surfaces. So while it is always a good practice to disinfect the bench area where any diseased plant was growing, the aerial spores do not pose a long-term sanitation issue.”

5. Apply Fungicides Preventively

Growers should plan a chemical control strategy that will keep downy mildew in check all season long, at retail as well as in the garden setting, says Cornell University Plant Pathologist Margery Daughtrey.

“Growers bringing in plants from another business must treat on arrival with a systemic fungicide, unless the supplier has just made a treatment,” she says. ”Some may want to treat with fungicides that have different modes of action in rotation; others may want to watch for symptoms before discarding diseased plants and protect the remainder of their crop for the rest of the season.”

Preventive fungicide applications should be made at timely intervals, especially if growing at the same time that Impatiens walleriana are present in the landscape.

“Apply fungicides preventively beginning about two weeks after sowing or sticking, and re-apply them on a weekly schedule,” Warfield says. “Be careful to rotate among effective products that have a different mode of action (as designated by the Fungicide Resistance Action Commitee) to avoid the development of fungicide resistance within the pathogen population.”

6. Inform Retail Customers

Retailers should be informed that although plants may be healthy at their stores, they can be infected once planted into the landscape. Instruct retailers to avoid using impatiens in the same flowerbeds planted with impatiens in 2011 to avoid a reoccurrence of the disease due to overwintering, Daughtrey says.

7. Consider Alternatives

Research shows some plants are not susceptible to downy mildew. This makes them good choices for growers to offer landscapers and gardeners in order to help minimize the disease. Among the unaffected plants are Sakata’s SunPatiens and Ball FloraPlant’s Celebration and Fanfare New Guinea trailers.

Topics:

Leave a Reply

3 comments on “7 Tips For Protecting Impatiens From Downy Mildew

  1. I applied Copper fungicide and arrested Downey somewhat, thereby keeping the bed of I. Walleriana under my Crabapple tree looking 75% sofar. this is now August 19 near Columbus, Ohio. Do you recommend treating the planting bed with a fungicide like Captan in the late fall and again in very early spring prior to re-planting?? Jim Frobase, Horticulturist

  2. Cured my IDM—-25 year landscape contractor in Birmingham. At my resident I plant a lot of impatiens 450 to 500. All of my flowers got infected including my hanging baskets middle of June. I experimented with fungicides—-the flowers i managed to save were treated with Mancozeb (Twice the label rate) then seven days later treated with copper sulfate ( Bodine Brand–powder) full rate then three days later full rate again. The impatiens that were not down to anything but stems came back and flushed. I have not treated again. Continued light watering during treatment. Hanging baskets came back as well. I’ll keep planting them—so beautiful

More From Disease Control...
Researchers Study Rose Varieties

October 17, 2017

Rose Rosette Update: Research into Detection and Management Continues

Halfway through a five-year, $4.6 million grant to combat rose rosette disease in the U.S., a national research team is encouraged by the amount of information learned, but admits having a way to go before finding how to overcome the deadly problem.

Read More
Botrytis Symptoms on Leaves

October 17, 2017

How One Grower is Battling Botrytis with a New Biological

CropKing in Lodi, OH, recently began using a new beneficial fungus in its fight against Botrytis in its greenhouse tomatoes. So far, the results have been promising.

Read More
BASF Pageant

September 29, 2017

New Fungicide Provides Production and Postharvest Disease Control in Ornamental Crops

Pageant TR from BASF controls seven key diseases, and can be used both in the greenhouse and in trucks that are on their way to a retail site.

Read More
Latest Stories
Researchers Study Rose Varieties

October 17, 2017

Rose Rosette Update: Research into Detection and Manage…

Halfway through a five-year, $4.6 million grant to combat rose rosette disease in the U.S., a national research team is encouraged by the amount of information learned, but admits having a way to go before finding how to overcome the deadly problem.

Read More
Botrytis Symptoms on Leaves

October 17, 2017

How One Grower is Battling Botrytis with a New Biologic…

CropKing in Lodi, OH, recently began using a new beneficial fungus in its fight against Botrytis in its greenhouse tomatoes. So far, the results have been promising.

Read More
BASF Pageant

September 29, 2017

New Fungicide Provides Production and Postharvest Disea…

Pageant TR from BASF controls seven key diseases, and can be used both in the greenhouse and in trucks that are on their way to a retail site.

Read More
Ascochyta in chrysanthemum

September 27, 2017

14 Common Chrysanthemum Diseases to Monitor

Penn State University Extension features a section on its website devoted to diseases commonly found in chrysanthemums.

Read More
Boxwood Blight

September 19, 2017

Concerned About Boxwood Blight? Here Are Some Updated M…

AmericanHort’s Horticultural Research Institute has released an updated version of its boxwood blight Best Management Practices document.

Read More
Powdery mildew on rosemary. Photo credit: SHS Griffin

September 9, 2017

Howler Biological Fungicide from AgBiome Gains EPA Appr…

Howler provides preventive, long-lasting activity on a broad spectrum of soilborne and foliar diseases, with no special handling or storage required.

Read More
Aphids

July 7, 2017

New Tools for Your Crop Protection Arsenal in the Green…

Over the past few months, crop protection companies have developed several new products designed to help you manage a wide range of insect and disease pests. Here’s a look at some of them.

Read More
Primula acaulis, Botrytis, Disease, Griffin Greenhouse Supplies

May 30, 2017

BioWorks Launches New Biofungicide for Botrytis Control

BotryStop was developed for the control of pathogens such as Botrytis, Sclerotinia, and Monilinia in several crops, including ornamentals.

Read More
Botrytis Blight Geranium

May 10, 2017

A Refresher on Botrytis Management in the Greenhouse

When the weather is moist and humid, susceptible greenhouse plants may need to be protected from Botrytis cinerea, a fungus that causes leaf spots, blighting, and stem cankers.

Read More
Downy mildew sporulation on underside of leaf

May 5, 2017

New Bactericide/Fungicide from BioSafe Systems Helps Ma…

BioSafe Systems has introduced PerCarb, a broad-spectrum bactericide/fungicide for use in greenhouse fruits and vegetables, as well as other crops.

Read More
Pythium

March 27, 2017

Florida Ornamental Growers Took a Hit in 2016 Thanks to…

While damage figures from the 2015-2016 winter rains are still being compiled, researchers have found that Phytophthora and Pythium caused severe destruction in many plants.

Read More

March 20, 2017

AgBiome’s New Zio Biofungicide Receives EPA Regis…

The new biofungicide is the first product from AgBiome, and will be marketed by SePRO Corp. in the ornamentals market.

Read More

February 26, 2017

AgBiome Will Enter the Ornamentals Market With a New Bi…

AgBiome, a young company with teammates steeped in decades of experience in the crop protection world, sees an opportunity to bring products to market that fill the existing gaps in plant protection. The company has partnered with SePRO to market and distribute Zio, a biological fungicide expecting EPA registration this spring.

Read More
Tomato Spotted Wilt Virus on Osteospormum

February 23, 2017

4 Pathogens to Prepare For in 2017

Early detection of disease and virus symptoms in the greenhouse is critical. One expert says there are a few pathogens in particular that growers should be monitoring.

Read More
Boxwood Blight

February 7, 2017

Boxwood Blight Detection in Illinois Has Growers on Ale…

Symptoms of boxwood blight, which can spread quickly in production facilities, include leaf spots, stem cankers, and defoliation.

Read More
downy-mildew-impatiens-feature

December 24, 2016

How Agronomic Programs Can Help You Successfully Manage…

To prevent problems before they start, make an agronomic program an essential part of your production plan.

Read More

December 19, 2016

Funding Allocated for Several Horticulture Pest Researc…

The USDA Animal and Plant Health Inspection Service has allocated millions in funding to research plant pests such as boxwood blight, downy mildew, and phytophthora.

Read More
Phytophthora On Poinsettia

November 23, 2016

Tips On How To Prevent Aerial Blight Spread In Poinsett…

According to Michigan State University experts, certain species of the pathogen Phytophthora, which is typically thought of as a root rot, can also cause issues above-ground.

Read More