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Janet Macunovich

Impatiens failures and downy mildew - we need to talk

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There's a terrible disease working its way across the continent and we need to know about it, talk about what we're seeing, and also sort it our from other impatiens trouble (such as drought- and heat stress).

 

We hope you've read our article about impatiens downy mildew in GardenAtoZ's What's Up news section. We'll post what else we hear here, and hope you will post news and questions here, too.

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Have some email from growers to the effect, "Good article, glad to see people being informed. But tell them how far and fast the spores can spread, so they understand that they may well have purchased clean plants but still developed mildew."

 

It's a good point. This fungus can spread a LONG way. Dozens, hundreds of miles from an infected bed if wind and humidity support them. If the windblown spores come to beds that have stressed plants in them -- drought stress, for example -- infection's almost assured. In a matter of a couple of weeks the plants may be toast.

 

In addition, this fungus may not be so new to the North American landscape as the recent news stories say. The USDA and pathologists report a disease as present in a given State/region based on confirmed reports by knowledgeable people. Others may have seen it and not known what it was, or that it could be/should be reported. Just as an example of how our reporting system can lag -- brown lipped snails were legion in our neighborhood in the 1950's, but only reported officially in Michigan in the 1990's. So the fungus may have been here and only recently gotten to strength, or found enough hosts, or the right other conditions...

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I purchased/planted 6 impatients in late May at one end of my house - In mid June I purchased/planted 6 more impatients at the other end - The first six obviously had downy mildew as they not only stopped growth but shriveled away to the point I could not find them when I returned home from an extended visit - The last group planted are growing and flowering as they normally do in that area........

 

After reading the downy mildew alert I did some "ground level" sleuthing and found remains of three of the diseased plants - what I found was a single stem that resembled a stem of poorly preforming moss rose, even the leaf that is trying to grow is pointed and rounded like a moss rose - Those 3 I can dispose of - what is the recommendation for the thriving impatients at the other end of the house border as I have marigolds and walleraina that are in the same bed but not presently infected???

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New question on impatien collapse (that's basically what happened to mine ):  is the ground where they were growing now infected ?  Can I plan more impatiens in the same places this coming spring?  Heard about the problem growers were having In Florida last winter with the mildew.  Hoped we had escaped here in the north.  My plants were beautiful for half the summer then, in a matter of weeks. they all died.  I blamed it on the heat, but was probably the mildew.

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I'd like to know about this as well, had pretty much the same scenario.  They were fine before we went on vacation for a week and even though we had a neighbor watering who is very relaible, it was crazy hot during that time.  When we arrived home I thought they just needed water, but they never did perk up even when I trimmed some of them back.  They all resembled impatiens that had gotten zapped by a frost, all skinny legs and few blooms.  Sadly, I pulled them out about a week before Garden A to Z reported on it, but I suspect we had the fungus too.

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Your story sounds like that we heard from a botanical garden horticulturist - went on vacation, came back, all the impatiens were down or going down. Matter of hundreds of flats, there...

 

As for whether the disease is now resident in your yard: Sadly, yes. Not only the ground where the plants were growing but probably all the ground for some distance around has downy mildew spores in it. So, too, do neighbors' yards, and the beds at office buildings and shopping centers. If infected beds are within a half mile of you, chances are pretty good that you'll see downy mildew again.

 

It's a very long lived disease in dormancy. And nearly impossible to control out in the open garden. In Europe, where downy mildew worked its way across the continent a decade ago, people just don't grow impatiens anymore. Here, some growers are NOT planning to grow impatiens this year, and some garden centers I've talked to are not going to stock them. Time to start thinking of other things to grow.

 

Barry Burton, past Detroit Zoo horticulturist and past City of Chicago Greening manager, is back in private practice and remarked to us this year that we might as well look on it as a good thing because we'll all be forced to be more inventive in the shade...

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This is why I am doing my grand experiment - trying to grow downy mildew resistant New Guinea impatiens myself. As these are so expensive (about $3.50 per plant), I'm hoping to grow enough of these myself to replace the 20 flats of regular impatiens I normally use in my shady yard. I bought 725 seeds from Jung and have 10 four foot shop lights and an newly extended plant table set up to accomodate my twenty flats. If this is successful, I will do this every year from now on. If not, then I will be back where I started - no impatiens. I'm hoping this works!

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The father of the propagation manager at Bordine's Nursery fold us a few weeks ago that his son said there would not be any impatiens available this year because of the disease that had swept the country.  He did not go into specifics.

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Okay, things are progressing on my project to grow my own New Guinea impatiens as a replacement to the regular/downy mildew version. I met with a greenhouse friend owner who has supplied me with several large bags of the proper ProMix growing seed starting and trnsplant media. I have 420 rooted cuttings on order as well as enough seeds on hand to start 400 more NG's from seed (Divine Mix from Jung, all colors). I have built a 4' by 14' plant table with 12 grow lights suspended over the table with adjustable chains in my basement. I am currently measuring the temperature and humidity swings in the basement and have humification and auxilliary heating equipment on hand to regulate the needed conditions. My 900 4" pots arrived today from the Greenhouse Megastore. I have the ping pong table cleared off and extra grow lights on hand if more space is needed. I am at war with you, Downy Mildew, and you may deny me regular impatiens, but by gosh, I will have New Guineas instead (or, I will waste an awful lot of money trying!). Charge!!! (that was a reference to my credit card of late ;) )post-1488-0-15458700-1361512524_thumb.jpg

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Margaret, in addition to New Guineas and the Torenia you mentioned as an impatiens alternative, here are a few more that I have been looking at;

 

- Browallia 

- Marmalade Orange Crossandra

 

The Browallia is a shade plant and is available in white and purple, so it should be something worth trying. Also, last year I did a trial in my front yard with orange Crossandra which receives very little direct sun and is in shade nearly all day. The Crossandra bloomed profusely despite being advertised as a "sun" plant! I will be buying more of this this year to try out in a few other locations in my yard.

post-1488-0-12389300-1361565907_thumb.jpg

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Ah, the basements, garages, storage sheds and such (including refrigerators) of gardeners are only understood by fellow gardeners and perhaps only tolerated by family members.

 

How old are they? You posted about the setup on Feb. 22, how long after that did you start them? How do you water them?

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Steven - all the larger ones are the rooted cuttings and have been potted up a couple weeks now and are looking great so far. Some are trying to bloom so I have been nipping off the buds so the energy goes into plant growth. I have a small watering can with a broad, downward facing sprinkler head attachment that I use to keep things moist. I lift the pots to gage by weight how wet things are - trying to strike the right balance between too wet and not wet enough. For the photos above, I had the lights up so I could work but normally, they are down about 2" above the plants.

 

The smaller tray is the New Guinea "Divine" seeds I ordered from Jung that I started on 3/15 in four 72 cell each flats. I followed the directions precisely, even monitoring in-soil temperature 24 hours a day to ensure everything stayed in the right range. I planted 450 seeds and by day 20, I only had 122 germinated. However, over the next two days, a die-off hit (not sure why) and I lost about 35 seedlings. The 80 or so ones left are now continuing to grow, but slowly. Just tiny little things compared to the robust cuttings. I'm quite disappointed in the seed results since I put in my best effort for success. I will continue to nurse the seedlings along to see what happens but for next year, I won't bother with them - I'll go cuttings only. I'm on my local garden walk this year on June 22nd and with a large percentage of my yard shade/part shade, I really do need the color impatiens give, so I've gone to measures far beyond what I might normally have done. My dear wife has kindly allowed my extravagence for this project :wub:

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Thanks Margaret :-) The cuttings continue to grow well and the plants I grew from seed (now 70 left) are about 3/4" high. I am assembling my 6' x 8' greenhouse tomorrow and if the warmer weather we are supposed to get holds, I will soon be moving the plants out of the basement and into the greenhouse.

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Update 5/14/13 - Here's a photo of my New Guineas in my green house. Tomorrow I'll start hardening them off outdoors and soon be planting them in my beds. Posting this to show that with an initial investment in the set up that it is feasible for a regular gardener to grow their own New Guineas at home to replace the standard impatiens impacted by Downy Mildew.

post-1488-0-61833900-1368594033_thumb.jpg

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I always meant to do a follow-up post to my experiment with growing my own New Guinea impatiens last year. My plants did extremely well and I couldn't have been more pleased. The New Guinea impatiens performed just as well as any store-bought versions I have ever tried and bloomed nicely all the way to frost. As I had heard, the New Guineas were indeed immune to the downy mildew which had ravaged my regular impatiens the summer of 2012. No downside to report at all. My cost using cuttings was $0.50 each. This does not include the cost of my setup with all of the lights, pots, soil and electricity. However, the setup and pots can now be used every year from now on. The key thing I found out was to grow from cuttings, not seed. Seeds were a disaster despite my very best efforts (heating pads, good light placement, careful soil moisture management, etc). After all the seeds I started with, I ended up with only 11 living plants by planting time, only about an inch tall! I planted them in my flower bed but they never bloomed and remained stunted all season until frost. These seeds came from Jung. Regarding my New Guineas, here is a photo from August (2013) of my plants doing nicely in my beds. As mentioned, they were beautiful until frost (unlike regular impatiens, that normally looked pretty dreadful by fall). I'll be doing this from now on (unless I can buy a flat of 48 New Guineas for $10 each, which isn't likely!).

post-1488-0-04101900-1392021006_thumb.jpg

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Margaret, I can well imagine how hard it must be keeping temps up in your greenhouse! I just used mine temporarily for a few weeks to harden off my plants, so luckily, I don't have to worry about winter heating.

 

To keep busy, I have been deciding on new native plants I want to order and also, planning a small expansion of my butterfly garden because I have run out of space for new plants LOL! In case you would like to see my last summer's butterfly garden, here is a photo ablum with a few photos: http://www.flickr.com/photos/60703385@N07/sets/72157639065730794/

 

I wish I lived closer to where you do Farmer's Markets so I could stop by. I really enjoy following your Sage posts and all of your adventures :-)

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