Dactylorhiza Black Death?

[Roderick]

Hi!

We are interested in wild orchids, but do not grow any.  In 2012 we visited dune slacks in the Gibraltar Point NR, Lincolnshire, on three occasions.  In one slack there were thousands of splendid spikes.  Dactylorhiza praetermissa and D. x grandis in almost equal numbers.  We saw no pure D. fuchsii in that slack.  It is said there were tens of thousands of spikes in 2013.  This year there were almost no flowers (Fig 1). 

On 10.05.14 emerging spikes and leaves were tipped in black (Fig 2).  On 7.06.14 spikes that had extended were shrivelled and blackened, by 15.07.14 almost all that remained was previous seasons flower stems.  Compare Figs 3, 4 & 5 taken between the same three fern clumps but not quite at the same viewing angle. Fig 3 is fine spikes on 23.06.12, Fig 4 dying spikes on 7.06.14 and Fig 5 just dead stems from 2013 on 15.07.14.   On 15.07.14 we returned to collect samples, with permission, (Figs 6 & 7).  Little remained above ground of most plants. 

To me the material matched the pictures of Cladosporium orchidis in the article by Maureen and Brian Wilson in “The Rock Garden”, 2001, 107, pp168-170.  The RHS Advisory Service however did not confirm this identification.  DNA sequencing did not match any previous record.   Samples were forwarded to Kew.  No identification was made. 

The RHS has requested fresh material from plants showing early symptoms in 2015.  We will try to send this.

If anyone has cultivated plants with similar symptoms in 2015 could we suggest they send material to RHS Gardening Advice at Wisley?  If you include Reference 12238/285401 2014 they ought to be able to collate results with my samples.

It should be easier to deal with infection in cultivated plants if the pathogen is identified!

Roderick

[Maggi Young]

Worrying that so far the RHS has not been able to make an ID.

Regarding  Cladosporium orchidis - this, and the Wilson's article, has been the subject of discussion in the forum over the years - I repeat here the image of the affected foliage from that article, plus the text of the article itself.
 Wilson Dact._diseasearticle- image.pdf (112.98 kB - downloaded 145 times.)

 Cladosprium orchidis_article.pdf (158.13 kB - downloaded 228 times.)

[SteveC2]

Hello Roderick,
Has it been established beyond all doubt that the tidal surge of December 2013 was not responsible for weakening the plants to allow the pathogens in?  I am no hydrologist but I would have thought that the huge amount of seawater which flooded the reserve must have had an effect via the groundwater.
Having said that, by the end of June, thirty miles away from Skegness, my entire Dactylorhiza collection had been killed by the fungus or burnt.  I have bought some replacement dacts and will be interested to see if the disease returns.

P.s. I have just realised that I emailed you in the summer via Kevin Wilson.

[Tony Willis]

Having had my plants wiped out by this disease I do not think the strength or weakness of the plants effected has any bearing on it.

I had a magnificent collection of really robust plants of several species. One I did not have was D. majalis and I accepted a single crown plant  which then died with the disease the following spring. Within two years my whole collection which were grown in pots  had gone. The first year several died and a few survived but were very badly diseased. The following year these all died.

At that time the problem was not widely known and whilst I realised it was easily spread and deadly I tried all the available fungicides to no avail. As it was I spent hours with a scapel peeling of the blacked outer leaves on the crowns hoping that the inner core of green would then grow out.  Had more information been available I would have destroyed them all the first year.
I am now trying again to build up a collection but with not much optimism.

Whilst growing the plants in pots many had self seeded into both my garden and also into my neighbours. These have continued to proliferate and although some die each year others are clumping up nicely so there must probably be some resistant plants.

[SteveC2]

Tony, I appreciate that people all around the country have had bad experiences with what has been labelled the "Black Death", including me,  but I was commenting on the very specific instance at Gibraltar Point NNR as mentioned by Roderick, where neither Kew nor the RHS could give a positive identification of the cause.

The Lincolnshire and Norfolk coasts were victim of a huge tidal surge in December 2013.  At GP this lead to several feet of sea water flooding much of the reserve.  An entire plant community on an area known as the Freshwater Marsh was lost, including tens of thousands of Dactylorhiza.  Species preferring higher salinity have already been recorded in large numbers.

The dune slacks that Roderick mentioned were not flooded, but the dacts have died and I was simply asking if it has been proven that groundwater movement had not increased the salinity of the soil, contributing to the death of what was quite simply the most spectacular display of wild orchids that I have ever seen.  It seems to me that it is quite a coincidence that two catastrophic events, the flood and an outbreak of disease, should have occurred so closely together and not be related.

[Roderick]

Hi Steve and Tony,

I can confirm the Freshwater Marsh was flooded for a long time with sea water.  Asphyxia and salt will have taken their toll.  Very few orchids showed this year.  Some species we did not see at all.  However the  D. fuchsii that did flower were not diseased. 

The 'Petrified Pool' was flooded with sea water and the pure D. praetermissa population there completely failed to show.  The East Dunes area with the disease was flooded by rising water, not by over-topping according to the Warden.   The mix of species of  broad leaved plants and ferns was unchanged whereas the Freshwater Marsh lost many species and was down to robust rushes and sedges with some grass.  There are higher areas round the edges of the East Dunes slack and the disease was present here where no flooding will have occurred. 

One adjacent higher and fenced area had excellent looking plants with no signs of disease.  We did not enter it as we could have been carrying spores on our boots and clothes.  We took photographs from afar and will return in 2015 to see what has happened.

Whether flooding and disease are related we could not tell, but their distribution was different.  Another factor this year was a large increase in herbivory, but the necrosis was not starting at the gnawed edges of the leaves.  Rabbits and deer are numerous in the slacks.

Roderick

[Tony Willis]

Steve

sorry if I misunderstood.

In 2006 I found a large colony of dactylorhiza mixed with platanthera growing in roadside grit on Shap in the Lake District,a very dry location,in complete contrast to the one you have described.

I have monitored this since then and by 2010 they had all but for an odd one succumbed to the black death.

Now they are slowly recovering and this year there were a few flowering size plants again

[mark smyth]

By far most of mine have died out also. The only survivor is Harold Esslemont

[johnstephen29]

Hi I live not far from Skegness and seeing the orchids at gp is what got me interested in these plants in the first place, it was an amazing site. I recently bought my first dactylorhiza from Anne, I hope it doesn't get infected by this disease.

[Graeme]

lost a few but funnily enough the pure white ones don't seem to have had any issues yet
D. fuchsii

[Lesley Cox]

I do hope this horrid condition never reaches NZ. This year mine have been wonderful, enjoying the cool soil conditions under a large spruce-like conifer.

[Roderick]

Disease update, help needed. 2016

The ‘Black Death’ progresses at the Gibraltar Point Nature Reserve.  Over most of the area there are no Dactylorhiza plants.  Where plants do remain the disease affects most of them.

I have sent samples of the ‘Black Death’ to the RHS and Kew.  No identification in 2014.  Fungus isolated and cultured from leaves and stems, excluding roots, in 2015.  Confirmed present in the leaf and stem lesions in 2016.  No identification made from morphology.  DNA sequencing showed nothing close.  Kew and CABI mycologists still cannot identify the genus from morphology and molecular techniques.  Suggestions are Cadophora  or Mycochaetophora, or close to them.  Host inoculation tests to prove the cultured fungus is the pathogen failed because the plants the RHS purchased from nurseries died of neck rot!

Can anyone suggest a source of healthy plants of D. praetermissa or D. x grandis for the RHS to try their tests on while they still have the fungus in culture?

Roderick

[Yann]

Roderick do plants have been introduced into the reserve (ex-vitro, spares)?
Cadophora can also affect DNA of seeds, so that's maybe a reason why the disease can be slow to develop once at adult stage.

Most of the nederlands nurseries have the problem with Dactylorhiza incarnata vitro plants.

You can try to contact Emanuel Hommes info@directplant.nl or Cruydt-Hoeck zaden@cruydthoeck.nl, they both can supply what you're looking for.