impatiens downy mildew forecast: too soon to tell

Impatiens Fusion Peach FrostI PRE-ORDER CERTAIN ANNUALS—reserving whole flats of favorites with my local garden center to make sure I won’t get shut out. Normally that early commitment includes a favorite peachy-colored impatiens, but this year, I’m not so sure. Impatiens downy mildew ravaged the popular bedding plant in many parts of the country last year, so I asked Margery Daughtrey, a plant pathologist and senior Extension associate with Cornell University, what the early line is from where she sits in her Suffolk County, Long Island, lab–and some substitutes I might consider for that annual order of mine.

First, a recap of what Impatiens downy mildew (the fungus-like Plasmopara obducens) looks like:

Did your impatiens seem to collapse in 2012? Early signs of infection may have been leaves that looked yellowish, as if the plant needed feeding, or foliage that curled under or seemed to wilt. Sometimes, a white material (the downy mildew) is visible on the undersides of leaves. Eventually, plants may defoliate, drop their flowers, and basically collapse. The fungus loves moist conditions and cool nights in particular. Particularly disturbing: symptoms happened earlier last year than before—as early as June.

The disease, which attacks Impatiens walleriana (the species our common shade-garden choice is bred from) showed up in 2012 first in Florida and later in the Mid-Atlantic, the Northeast, and even Utah and the West Coast. By Daughtrey’s count, 35 states had at least one case of the disease in 2012, and some Canadian provinces as well.

impatiens fusion glow

my q&a with cornell’s margery daughtrey

Q. I’ve been watching the trade publication “Greenhouse Grower” for news on impatiens downy mildew, and in a December article, you said that growers are of course well aware of the issues, and were making plans for 2013. Is there anything specific that’s “new” since?

A. Not really much change. The “Philadelphia Inquirer” did a story in February, but I noted that there were still impatiens being used as bedding plants at the Philly Flower Show!  “Southampton Press” [on Long Island] focused on the impatiens downy mildew in their Hampton Gardener column this week.

Stories are springing up here and there to educate the public about this disease, but until we actually get into the spring retail season for bedding plants, we won’t know whether growers gambled correctly on how many impatiens to grow for this year.  In some areas demand may be the same as before, and in others landscape gardeners and home gardeners may both be very skittish about planting impatiens.

Q. How are growers planning to offset the cutbacks in impatiens production?

A. Growers who know that the disease has been devastating in their area have cut back how many Impatiens walleriana they are growing this season, and are offering various begonias, coleus, New Guinea impatiens, torenias, etc. as alternatives.

Home gardeners should take this opportunity to look into exciting new annuals that may be new to them.  Many work very well in shade.  One of the most confusing things will be for them to realize that New Guinea impatiens do not get this particular disease—and that they do well in shade, as well as in sun.

Q. If gardeners had problems last year, is it possible that spores have overwintered? I read on Michigan State University’s site that this can happen.

A. Yes. Anyone who saw impatiens downy mildew last year really should not try to plant impatiens into that same flower bed this year.  The impatiens makes several kinds of spores, and one of them is designed for overwintering the pathogen.

Q. Europe has a widespread problem that began a few years before ours, correct? Have they managed to get past it, or is impatiens still a problem crop there? 

A. The disease was seen in Europe in 2003; then in the U.S. in California, New York and Tennessee in 2004, but only as a minor problem that appeared during greenhouse production—it did not create problems in the landscape. It has been seen occasionally in the States since.

The first landscape problem with impatiens downy mildew that I am aware of appeared in Saratoga Springs, New York, in 2009, and returned in 2010,  2011 and 2012 there. Southeastern New York had dramatic landscape problems in the fall of 2011 that returned beginning in June 2012. South Florida saw collapse of impatiens in the landscape in the winter of 2011, and this phenomenon returned in the winter of 2012.

As far as England and Europe: A recent column by Chris Beytes of “Grower Talks” magazine has the most recent info that I’ve seen. There is certainly still a problem there, but they are probably not as gaga about impatiens as Americans have been for the past 40-50 years.

Q. Are there web pages we can consult to keep track of how the season, and the disease, develop?

A. Lots of good things, all to be found here and edited recently. I’ve called out the most helpful portions below:

begonias, coleus and ‘annual color’ options

coleus spitfireI’M TAKING A GOOD LOOK at begonias and coleus, in particular, along with flowering plants that Margery Daughtrey recommended such as torenia, to add color to semi-shady spots where I place containers. Some things I like for “annual color” (often from their foliage alone) in such conditions:

  1. Carolyn says:

    So was the disease imported on the nursery stock? Would it be okay to plant them in containers in fresh soil? I don’t have much shade anyway, but I love the glow of masses of orange impatiens and their easy care nature.

    1. margaret says:

      Hi, Carolyn. Wholesalers who propagate or then “finish” impatiens to sell to garden centers and then to customer use repeat applications of fungicides to control it, but at every step in the process there’s a chance of infection and then spread. Infection was traced to nursery crops, yes, but now that it’s been out in the environment in 35 states it’s not known how long spores can overwinter in places where it occurred in previous years (some say 5-10 years) nor how far spores can blow in the wind (as in, from a neighbor’s or not)…meaning the risk may come not just from more problems in the nursery, but from spores in the landscape too.

  2. Liz Davey says:

    I plan to use more Browallia. It has performed well for me in sun-part shade areas of my gardens and I like its long lasting blue blooms.

  3. Jayne says:

    I lost all of my impatiens last year – one small hanging pot almost escaped, but finally succumbed to the wilt. Very sad to see a whole bed demolished. I won’t be using my gardening dollars on impatiens this year, but as you point out, it gives us a new sphere of plants to choose from – love the coleus as a substitute.

  4. Margit Van Schaick says:

    I read somewhere that growing impatiens from seed may help avoid the problem, if you can manage to provide adequate air circulation and otherwise avoid too humid conditions. I think it was a post by Leslie Land on her website.

    1. margaret says:

      Hi, Margit. That would help avert possible passalong disease from a wholesaler and a garden center, yes, but if the overwinter spores are already at your place from last year, or nearby (a neighbor’s garden, though they don’t know how close that has to be for the spores to blow in) you could still be hit with it if the weather conditions favor infection. (I think they like 10 weeks indoors counting back from final frost date, so even here I would have to better get started fast!)

  5. joy says:

    guess it’s similar to crop rotation–planting the same thing every year introduces problems. I never thought of it affecting a home garden, but makes sense. Well, here’s a good opp to try some new annuals!

  6. Onoosh says:

    “Repeat applications of fungicides…” Now, that’s a reminder to people like me, trying to combine wildlife/bird gardening with a certain amount of colorful garden frivolity, about wholesale growing necessities and practices. What’s your advice about the whole fungicide, pesticide and genetic engineering of plants question? I want a pretty garden (my husband does the functional and kitchen garden side) but I also want to protect my garden and–my top priority–my bird and wildlife environment.

    1. margaret says:

      Hi, Oonosh. Those are several different topics — genetic engineering and use of various chemicals. Greenhouse growing of bedding plants is traditionally a challenging job and various chemical controls are used. I think we have to be clear that unless we shop at a grower that’s certified organic or at least practices IPM (a least-toxic approach) we are bringing in plants (especially bedding plants or “annuals”) that have been treated in some way, at least with chemical fertilizers but usually other substances as well. The good news is that you don’t eat impatiens or begonias. My local garden center has a small section of plants from an organic grower, but not the same wide selection as conventionally grown stuff. Growing your own from seed guarantees what you’ll get of course! I don’t use garden chemicals, but I do buy some bedding annuals that were not produced organically.

      As for genetic engineering, read here and here.

  7. Amy says:

    Would love to know who you pre-order from locally Margaret, as I live nearby. I always covet your orange pansies which I can never find. Great garden talk yesterday, by the way! Can’t wait to plant my new seeds!

    1. margaret says:

      Hi, Amy. Glad you enjoyed y’day — me too. What a great group. Most nurseries will accommodate if you ask early (now!) and for instance Ward’s in Great Barrington will get orange pansies but they do sell out fast. Have someone like that set aside a flat of orange for you by calling now.

  8. Colleen says:

    Margaret my question is off the subject. My beds that are shaded are all along my property line. Shaded by mature trees. The beds are covered by leaves . I usually rake them all out in the spring. I have over several bulbs planted in these beds that spring up through the leaves with no problem. I would like to plant shade loving flowers but the ground is hard I believe because of all the tree roots. If I turn the leaves into the soil will this help to soften it ? What is you’re suggestion?

  9. Tillie says:

    I switched to perennial lamium for my shaded areas several years ago – the archangel variety which blooms a nice yellow for about five weeks and has great foliage the rest of the year, and the ordinary variety that blooms mauvish, pinkish or white for much of the summer – white nancy and red nancy as just two of the varieties. Annuals were getting too expensive and I am looking at my senior years, looking to cut back on work. If I want a splash of colour I put a pot of nonstop begonia out as well, storing the corm over the winter in a net orange bag, hanging in an airy dark place (Margaret’s idea for garlic).

  10. june says:

    Torenia is a great choice for shade/light sun but hard to find.
    You’d think the garden centers would be full of that this year instead of the usual begonias (which also do well, but, more variety would be nice)

  11. Tom Mann says:

    Like many, we would always buy flats, but we would always dig up and relocate plants that had self-seeded. By mid-Summer, those plants were just as showy as those purchased in the Spring ‘with a purpose in mind’ We use the homegrowns as fillers in the shade and for extra containers on the covered porches. Here’s hoping for more re-seeds this spring.

  12. Alan Grossberg says:

    FWIW, most medium and long-range forecasters are predicting a continuation of current weather conditions until at least mid-April for the mid-Atlantic and Northeast…in other words, a year without much of a spring…and then a sudden flip to warm, followed by a hot and dry summer. If this verifies, impatiens will be much happier, at least from a meteorological standpoint.

  13. Linda says:

    No impatiens here this year! Mine, and my clients’ – singles and doubles, and everyone else’s I know of all collapsed here last year starting in July. I’ll be using Torenias, Dragon Wings and other begonias, browalias, and coleus instead. Maybe I’ll try a few New Guineas, but they’ve had problems of their own in our area in recent years. Even nurseries have had to dump many of them. I think it’s some kind of viral disease. I find New Guineas don’t bloom nearly as well as the wallerianas in part sun, unfortunately. And one of my best clients, who has only shade and part sun HATES coleus. :~(

  14. Susan says:

    I like your alternatives to impatiens. Be aware though that there are diseases that take out these plants as well such as Coleus Downy Mildew (a different pathogen from Impatiens Downy Mildew). I think one of the keys to remember here is to avoid replanting in mass large sweeps, the same plant in the same place, year after year. Think of having a rotational flower planting like you would do in a vegetable garden.

  15. Heather says:

    We own a garden center in Keene, NY (in the Adirondacks) and we grow all of our annuals with organic fertilizer, soil, fungicides and insecticides. We did not have any problems with downy mildew on our impatiens last year, although people did report having the mildew at their homes. Still, I hesitated on growing “regular” impatiens this year and instead have opted for many varieties of New Guinea impatiens, begonias, fuchsias, coleus, browalia, torenia, lamium, diamond frost euphorbia, etc. There are several fungicides available that are OMRI listed, but it doesn’t seem like there have been any recommendations for using a fungicide to mitigate this problem. I’ve been wondering if copper fungicide might do the trick; it saved our tomatoes from the blight last year and the ones that weren’t treated succumbed. The fungicide that I used in the greenhouse is called RootShield and it’s applied as a drench during the early growing stages. I have been wondering if I could attribute our success to the RootShield, but I’m not positive.

    1. margaret says:

      Thanks, Glenda. The MSU folks and Margery D. of Cornell (from the story) have been working on this disease together intensively.

      Hello, Heather. The chemical fungicide protocol in conventional greenhouse culture is about “prevention” they say and starts at transplant I believe and is repeated every 7 days. I haven’t seen any organic control suggestions.

      Hi, Alan. I will always pray for rain over dry, even if it means good conditions for unwanted fungal and fungus-like issues! :)

  16. Tim says:

    Interesting…… I grew grapes for nine years out on Long Island, NY. Downy & Powdery Mildew were a constant threat. The organic antidote was sulfur and pepper oil sprays every 7-10 days between mid-April and early October. Not sure of that could be applicable to Impatiens and Coleus, but either way, a lot of work.

  17. Mary Withrow says:

    I love impatients and will take my chance! But I read sometime back that plants can store diseases for up to 100 years? Is that true and what type of diseases can they store?

  18. This clearly demonstrates the dangers of shipping plants all over the country instead of growing and selling plants locally. Its also a good reason to rotate your selections on a yearly basis and to plant a diverse variety of plants.

  19. Kathleen Norris says:

    Hi Everyone! I massed Impatients in an oval garden here for about 3-4 years and they were splendid of course in vibrant color. Shade moist soil. Then last year I replaced them with Monkey Flower which was also very attractive. Will see how they come back this year. Monkey Flower is listed as “annual” but they have come back in another garden every year and self seeded quite well spreading on their own. Just a thought if you have had problems with Impatients.

  20. ken york says:

    My practice for many years has been to use tuberous begonias as bedding plants. Impatients just don’t compare. Used to get the seeds from Blackmore and Langdon and Antonellis, then saved my own seed. They each advertised theirs as the world’s finist, Most growers here abouts grow nonstops. It’s too late to grow your own now as they need to be started the middle of December for early June putting out.. They go good with hostas anbd fern beds.

  21. Nelson says:

    “Coleus is a good choice. I love the different colored leaves.”

    Definitely agree on this one. As well they can be grown bushy and compact, or they are sometimes trained on one stem to look more like a tree.

    1. margaret says:

      Hi, Nelson. I’ve ordered a couple of coleus that I plant to rely on and will probably shop for more in the spring. I love fancy leaf “houseplant” begonias for the same reason. Actually, I don’t mind being without flowers for the most part…but I did love those peach-color impatiens! :)

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