Dactylorhiza disease

[Peter Maguire]

Does anyone recognise this as being the problem that decimates Dactylorhiza collections? The plant is Dactylorhiza praetermissa and was healthy last year, but shortly after emerging this year started to go brown at the leaf bases. If the brown markings were at the leaf tips I would assume it was scorching, but this seems to originate at the base, and I wondered whether it was the fungal disease Cladosporium orchidis that Brian and Maureen Wilson wrote about in The Rock Garden in 2001. So far there is no sign of yellowing around the brown markings that they describe, but I have taken the precaution of isolating the plant (it's in the garden at work, 8km away as the aphid flies)

[Maggi Young]

Looks suspicious, Peter.
Here, for others, is the photo of an infected plant from the Wilsons, used to illustrate their article, plus a pdf of the article from that issue ofThe Rock Garden of 2001



 Cladosprium orchidis_article.pdf (158.13 kB - downloaded 556 times.)

[mark smyth]

  I can only see the article in Japanese

[Maggi Young]

Well, I could say that was for the benefit of our Japanese readers, Mark... but it's just opened okay for me... in English!

[mark smyth]

I'll read it the old fashioned way with the bulletin in my hand

[Jeff Hutchings]

Peter,

I have had the same problem with odd plants from different species this spring. As you write, the damage is low down on the leaf and rapidly decimates the whole of the plant. It started to appear after the hot period we had a couple of weeks ago which was then followed by a couple of very cold days which were windy. I wonder if the leaves are initially mechanically damaged and then the bacterial rot sets in. Also I increased the watering rate when the temperature was high but did not reduce the frequency when the cold came so the plants were rather damp.

[Anthony Darby]

Isn't it a fungus? I have heard that mulching the plants in the autumn prevents reinfection in the spring. I have had success with a systemic fungicide, or that may just be a coincidence?

[Neil]

Isn't it a fungus? I have heard that mulching the plants in the autumn prevents reinfection in the spring. I have had success with a systemic fungicide, or that may just be a coincidence?

Mulching makes no difference I have it back again after being clear of it last year  so the plants are in isolation round my brothers garden  and being treated with systemic fungicide, once they have died back I will empty them out of the pots, clean them up dip them in the fungicide, bring them home and then dip them in the fungicide again and repot them.  All the while spraying the rest of the Dacts here.  Oh and praying very hard for it not to return next year. 

[Tony Willis]

Neil

in my experience once an individual plant has got it there is no way back, it will die.I found that the growing point on the new tuber is black and shell like and that is the end. I have tried peeling it back with a scapel to healthy tissue inside but then that just blackened and so on until nothing was left.

[Neil]

No I have managed to save some of them , but those do come back smaller, this year it was only 1 pot that is infected so as I said I am praying hard.

[mark smyth]

I might have an infected plant or I might have damaged the nose while weeding. I'll take a photo

[Peter Maguire]

Update:
The Dactylorhiza praetermissa rotted away to nothing within a few weeks of the photo being taken. No sign of it recurring this year (yet), so hopefully the swift removal of the infected plant has prevented the infection spreading to other plants.

[mark smyth]

Does black death eventually disappear in the garden or do I have it forever?

Despite being knocked back every year those that I potted continue to make new tubers and are just coming in to growth

[Maggi Young]

A reminder that there is also a thread  on this disease in the Cultivation Problems section: http://www.srgc.net/forum/index.php?topic=566.0

I have merged  Mark's new thread  to this page