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

2 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

More From Disease Control...
Basil_Persian-AAS2015_620x329

July 31, 2015

All-America Selections Promotes Garden-Fresh Cooking

All-America Selections (AAS) has stepped forward with another first when promoting AAS Winners, this time in the form of cooking videos using vegetables/edibles that have performed extremely well in the AAS Trials. These days, a love of gardening is directly related to a passion for cooking. Tying the two together is a natural when marketing joys of cooking with fresh vegetables from the garden and farm market. After 82 years of conducting trials where only the best performers are declared AAS Winners, the organization now has more than 325 individual varieties that have been “Tested Nationally & Proven Locally.” It is some of these many varieties that culinary storyteller, entertainer and horticulture industry veteran Jonathan Bardzik will use in a series of five videos demonstrating cooking techniques with AAS Winning herbs and vegetables. “I am excited to partner with All-America Selections to show people across the country that AAS Winners perform […]

Read More
Burpee Home Gardens Brand Adds Flowers

July 31, 2015

4 Reasons Retailers Snub National Brands

Greenhouse Grower’s lead editor, Laura Drotleff, and I got into a debate about why garden retailers, especially independent garden centers, snub marketing efforts from breeders and growers. She was very much on the breeders’ and growers’ side, expressing frustration about how limited retailers’ vision can be on the topic. I’ve reported on the garden retail side of the industry since 1998, about the same length of time Laura has reported on growers. I’ve heard a lot of retailer views on this, so allow me to share the most common reasons why retailers decline free marketing: Costs. While the marketing materials are free, and sometimes advertising, participating in these projects usually requires minimum orders. From a grower’s perspective, the minimum orders are reasonable. If garden stores promote a plant line, they need to have enough supplies to satisfy demand. From a retail perspective, if inventory reports show a plant line can […]

Read More
llan Armitage Syngenta Starcluster

July 30, 2015

Let’s Talk About Starflowers. Why Is Pentas Not More Popular?

It is good to talk about production techniques, performance results and then to see how our friends garden. Diversity of plant material has always been a strength in American garden centers, and we should never run out of plants to get people excited. However, perhaps people are tired of Petunias or Callas or Geraniums, but we will never run out of options to put in front of them. One plant that is often overlooked is Pentas, a fabulous summer crop for late spring sales. These are heat-tolerant plants, and growing them below 65°F in the greenhouse results in significant delay. Fertility should be at least 150ppm nitrogen, but avoid ammonia in the fertilizer. Plants are best grown at a somewhat higher pH than usual, between 6.4 to 6.8. For best presentation, pinch out the center bud. Side flowers will bloom together, and plants will walk off the shelf. Garden centers […]

Read More
Latest Stories
r3bv2 disease

May 20, 2015

SAF And AmericanHort Ask Government To Take Ralstonia O…

The Society of American Florists (SAF) and AmericanHort want Ralstonia solanacearum, Race 3, Biovar 2 (R3Bv2) taken off a list of animal and plant diseases that the federal government has determined could be misused as terrorist weapons. SAF and AmericanHort submitted formal comments together on the horticulture industry’s science-backed position on the matter. According to Lin Schmale, SAF’s senior director of government relations, extensive research has proven R3Bv2 does not belong on the government’s list of animal and plant diseases that can be misused as terrorist weapons. Every two years, USDA’s Animal and Plant Health Inspection Service (APHIS) requests a public review of the Select Agent list, asking for comments on whether plant or animal diseases should be taken off the current list or added to it. In the floral industry, R3Bv2 can have a devastating impact on geranium (pelargonium) crops, Schmale says, and both the potato and tomato industries also could be adversely affected by introduction […]

Read More
empress-intrinsic-brand-fungicide

May 13, 2015

BASF’s Empress Intrinsic Fungicide Is Approved Fo…

BASF’s Empress Intrinsic brand fungicide received supplemental labeling, providing California growers with an effective drench fungicide for disease control and plant health. The supplemental labeling is for use on herbaceous and woody plants in greenhouse, nursery container and field production in California. Empress Intrinsic fungicide provides protection against the four major root and crown disease pathogens: fusarium, phytophthora, pythium and rhizoctonia. Research shows Intrinsic fungicides control the broadest range of ornamental diseases while improving plant resilience to quality and reducing stresses that commonly occur during commercial production, handling and transportation. “More and more growers across the country are discovering the benefits of Empress Intrinisic brand fungicide treatments at propagation for rooted plugs, cuttings and seedlings, and in drench applications on transplants during the production cycle to protect against the major root diseases,“ says Joe Lara, senior product manager for BASF ornamentals. “A BASF fungicide program utilizing Pageant Intrinsic and Empress Intrinsic […]

Read More

April 20, 2015

Three Michigan State University On-Demand Webinars Offe…

The first rule of effective insect and disease control for vegetables is to take action to prevent problems before they occur. But in order to do that, you need to have an effective pest and disease management strategy in place that incorporates best practices to ensure a successful outcome. Michigan State University offers three pest and disease management on-demand webinars that will get you started and keep you on the right track.

Read More

April 15, 2015

BASF’s Pageant Intrinsic Fungicide Registration A…

The state of California has approved the supplemental label registration of Pageant Intrinsic brand fungicide for disease control in the commercial production of greenhouse-grown tomatoes and tomato transplants for the home consumer market.

Read More
OxiPhos_BioSafe2

March 23, 2015

BioSafe Makes Label Changes To OxiPhos And ZeroTol 2.0

There have been some recent label changes made to the BioSafe Systems product OxiPhos, a systemic bactericide/fungicide that reduces downy mildew spores when tank mixed with ZeroTol 2.0.

Read More
Nufarm_logo

March 23, 2015

Nufarm Fungicides Now Registered For Use On Edible Crop…

Nufarm Americas announced label expansions for two of its fungicides that will provide more pest management options for the ornamental industry. The Cleary 3336 F and EG fungicides are now registered for use across a wider range of edible crops, including select greenhouse vegetables and transplants, herbs and backyard fruit.

Read More
ColeusDMLeafSporulation_Daughtrey

March 11, 2015

Research Gives Clues For Preventing Coleus Downy Mildew

Maintaining awareness of coleus downy mildew is more important than ever to safeguard these attractive plants for reliable garden performance.

Read More
Rose Rosette on Knockout rose, May 2013. Photo credit: Alan Windham, University of Tennessee

March 2, 2015

Rose Rosette Disease Fight Gets A Boost From Government…

In 2014, $4.6 million was awarded through the Farm Bill to tackle rose rosette disease, a devastating pathogen that affects one of the industry’s most important crops.

Read More
Fig 1 Leafy Gall On Leucanthemum Becky

March 2, 2015

How To Prevent Leafy Gall Before You Lose Plants

Leafy gall is a nasty disease that can go undetected until plant damage is done. Take these steps to protect your crops from infection.

Read More

October 6, 2014

EPA Registration Granted To Stockton’s Timorex Go…

Timorex Gold, a broad spectrum fungicide, has received EPA registration in the U.S. for disease control on organic and conventional crops.

Read More

August 5, 2014

Prevention Measures For Impatiens Downy Mildew Start At…

Impatiens downy mildew is a fast-moving disease that can quickly go from bad to worse if conditions are right. In case you missed it, here are some of the highlights from Ann Chase's (Agricultural Consulting) downy mildew update at Cultivate'14.

Read More

July 22, 2014

Spray Coverage Key To Uniform Pest And Disease Control …

Greenhouse growers need to understand proper spray application coverage when applying pesticides and growth regulators to ensure successful treatment results.

Read More
Jeff Rich

July 18, 2014

Removing The Mask Of Phytophthora

Phytophthora is the number one disease of floriculture and nursery crops nationwide. Here are some effective measures growers can take to reduce the occurance of this pathogen, known as "the plant destroyer."

Read More

June 27, 2014

Biocontrols Can Be Highly Effective With Serious Commit…

Biocontrols can be very effective when the greenhouse operator makes a serious commitment to using them for integrated pest control. See how Parkway Gardens has successfully used biocontrols for the last nine years.

Read More

May 1, 2014

Be On The Lookout For Botrytis Blight

Greenhouse growers will be challenged by weather forecasts for cloudy and rainy conditions favoring Botrytis blight. Remembering cultural practices and correct fungicides will help until we get more sunshine.

Read More

April 18, 2014

Growth Products Introduces Improved Packaging For Compa…

Following the suggestion of a user of Companion Biological Fungicide, Growth Products has made improvements to the product's packaging to make it easier to handle and more durable.

Read More

April 8, 2014

Switching To Organic Fertilizer

Growers of short-term vegetable or ornamental crops should have an easier time switching from conventional mineral fertilizers to organic fertilizers.

Read More
Edema om Ivy Geranium. Photo credit: SHS Griffin

March 27, 2014

Geranium Leaf Spots: Is it Rust or Edema?

Damp conditions can lead to both rust and edema in geranium. Here's some advice on scouting and treating each.

Read More