The info you seek is on the Impatiens forum.

My spouse uses annuals in pots and as fillers.

She stopped using the popular semi-shade/shade impatiens (Impatiens walleriana) last year, due to the downy mildew (Plasmopara obducens).

That mildew was first recorded in the wild in Vermont in 1897. It's first horticultural appearance was in commercial greenhouses was in Britain 2002/2003 (maybe in imported plant material). Infected impatiens were first recorded in the U.S. in Massachusetts in 2005. The problem is now common in the U.S. and Canada.

There is no cure. Commercial treatment with fungicides in Britain failed. A number of U.S. and Canadian garden centres have now said that they will not sell these impatiens.

Personally, I'd say that the role the horticultural industry has had in the establishment and distribution of this disease is noteworthy. I'd presume it parallels some disease problems discussed by perennial gardeners on GardenWeb.

This post was edited by SunnyBorders on Wed, Jan 8, 14 at 16:44

Well, I went to the impatiens forum just out of curiosity and could not find the answer (on the first page anyway). I suspect the poster over there who said scientists and growers are trying to find a solution(but haven't as yet) is correct.

So, basically Char, it appears there is no answer yet and nothing on the horizon as far as anyone knows. It's such a shame because I loved adding them for color in among the hosta and other shade plants I have.

Maybe some of these threads will help. There has been discussion on the Annuals Forum as well as the Impatiens Forum.

Here is a link that might be useful: Impatiens Downy Mildew

It's too bad that standard Impatiens are pretty much out of the running now as beddng plants. But this opens up the field for good alternatives.

It also appears that both New Guinea impatiens and the "sunpatiens" varieties are resistant to the fungus.

A number of U.S. and Canadian garden centres have now said that they will not sell these impatiens.

And yet too many still sold them last year....irresponsible in my opinion.

As 'eric' referenced in his post I had good success using "sunpatiens" this past summer.

(Here are 3 white ones from sometime last July)

And as always I am pleased with the performance of annual wax begonias. They do well in sun and shade.

Very pretty, Rouge.

Don't remember seeing white sunshine impatiens before.

Think white is very useful for standing out in more shaded locations.

Yes, I love using the white impatiens in my shade beds, so I'm very disappointed.

So, I know the New Guinea and I guess the "sunpatiens" (never heard of these!) do well (or better than the "regular" impatiens) in the sun, but do they do well in the shade, or do they "need" more sun to thrive? I have beds that never see the light of the sun, lol.

Dee

It is my understanding that "Sunpatiens" are not as shade tolerant as the walleriana impatiens.

But I have also read that the white "Sunpatiens" do better in the shade than other color varieties of "Sunpatiens"...not sure if that makes sense.

In any event the white did very well for me last season.

Growers can spray impatiens with an anti-downy mildew spray that keeps the disease at bay for roughly two weeks -- long enough to get to market and sell. This is an incredibly irresponsible practice though because the spray is not available for consumer use and the protection wears off shortly after purchase.

The good news was that last season it seemed to take the downy mildew awhile to overcome the impatiens in my area -- it was mid-August or so before I saw massive impacts on the plants. Maybe this is an indication that the plants are building some resistance (?) or the grower sprays worked longer than expected. The unfortunate thing is that the mildew spores live in the soil so it never really goes away.

There really is no excellent replacement for impatiens in the shade landscape so I am really hoping that someone can breed downy mildew resistance into the species.

Very interesting, Mistascott.

I had impatiens the last two summer in large pots in my front yard. For the most part, they looked great.

Thanks, Rouge - that did make sense, lol! Maybe I'll give the sunpatiens a try in some of the brighter shade beds. They look quite nice in your photo.

Dee