I have a long-established Cotinus coggyria that has started to
suffer from a very weird dieback. This affects some branches
(but only some of the shoots on them) and some stray shoots.
I tried cutting it back beyond the affected parts, but with
little effect.

http://i41.tinypic.com/15ckn7q.jpg
http://i43.tinypic.com/15s81g1.jpg
http://i40.tinypic.com/2i1msmd.jpg
http://i42.tinypic.com/b9br41.jpg

It is over 30 years old, and I think that it has been suffering
from the last few years' wetness. My inclination is to cut it
back hard, to neaten it up, and otherwise see what happens. But
it's annoying, as it is unsightly when it happens, which is usually
sometime in mid-summer.

Any ideas of what is going on?

Regards,
Nick Maclaren.

On 24/01/2014 15:35, Nick Maclaren wrote:
I have a long-established Cotinus coggyria that has started to
suffer from a very weird dieback. This affects some branches
(but only some of the shoots on them) and some stray shoots.
I tried cutting it back beyond the affected parts, but with
little effect.

http://i41.tinypic.com/15ckn7q.jpg
http://i43.tinypic.com/15s81g1.jpg
http://i40.tinypic.com/2i1msmd.jpg
http://i42.tinypic.com/b9br41.jpg

It is over 30 years old, and I think that it has been suffering
from the last few years' wetness. My inclination is to cut it
back hard, to neaten it up, and otherwise see what happens. But
it's annoying, as it is unsightly when it happens, which is usually
sometime in mid-summer.

Any ideas of what is going on?

Regards,
Nick Maclaren.




I would hazard a fairly intelligent guess at Phytophthora. It seems to
be made worse by winter wet, but presents symptoms in summer. I lost a
Cryptomeria to it.

You might as well follow your instincts and cut it back, but I doubt it
will recover well given that the roots will be affected. If it is
precious, you could try deeply spiking the ground locally to improve
drainage/compaction, then using something like Rootgrow to encourage
root recovery. However, I think that will probably just be a stay of
execution rather than a miracle cure.

Wish it were better news :~(.

--
Spider.
On high ground in SE London
gardening on heavy clay

In article ,
Spider wrote:

Thanks for your response.

I would hazard a fairly intelligent guess at Phytophthora. It seems to
be made worse by winter wet, but presents symptoms in summer. I lost a
Cryptomeria to it.

If it is, it is behaving very strangely. But it may be an anomalous
reaction.

You might as well follow your instincts and cut it back, but I doubt it
will recover well given that the roots will be affected. If it is
precious, you could try deeply spiking the ground locally to improve
drainage/compaction, then using something like Rootgrow to encourage
root recovery. However, I think that will probably just be a stay of
execution rather than a miracle cure.

I think it very unlikely that the roots are seriously affected, as
this has been going on for a few years (though this was the worst
year yet), under 10% of the plant is affected at any one time, and
the rest of it is as vigorous as before.

A couple of the pictures I posted show clearly that the cause of the
leaf whitening is that the branches are dying round much of their
circumference. Phytophthora, it may be well be - but whatever it is,
it seems to be primarily a branch effect.


Regards,
Nick Maclaren.

In article ,
Nick Maclaren wrote:

A couple of the pictures I posted show clearly that the cause of the
leaf whitening is that the branches are dying round much of their
circumference. Phytophthora, it may be well be - but whatever it is,
it seems to be primarily a branch effect.

Sorry about following up to myself. I have just done a few searches,
and get some near-match on Verticillium, but one thing that really
baffles me is the leaf bleaching. The other is just HOW patchy it
is - those leaf pictures were a single branch.


Regards,
Nick Maclaren.

On 24/01/2014 19:22, Nick Maclaren wrote:
In article ,
Nick Maclaren wrote:

A couple of the pictures I posted show clearly that the cause of the
leaf whitening is that the branches are dying round much of their
circumference. Phytophthora, it may be well be - but whatever it is,
it seems to be primarily a branch effect.

Sorry about following up to myself. I have just done a few searches,
and get some near-match on Verticillium, but one thing that really
baffles me is the leaf bleaching. The other is just HOW patchy it
is - those leaf pictures were a single branch.


Regards,
Nick Maclaren.




When my tree was affected the local tree surgeon said it was
Phytophthora, but I confess there are elements of Verticillium, too.
It's my bedtime now, so too late to look up verticillium images.
I'm still inclined to blame the very wet winters we've all had, and that
seems to be how Phytophthora works, as I understand it, but I don't rule
out Verticillium now that you come to mention it. More research is
required ... or another urgler.

--
Spider.
On high ground in SE London
gardening on heavy clay

In article ,
Spider wrote:

When my tree was affected the local tree surgeon said it was
Phytophthora, but I confess there are elements of Verticillium, too.
It's my bedtime now, so too late to look up verticillium images.
I'm still inclined to blame the very wet winters we've all had, and that
seems to be how Phytophthora works, as I understand it, but I don't rule
out Verticillium now that you come to mention it. More research is
required ... or another urgler.

It wouldn't surprise me if a diagnosis of Phytophthora or Verticillium
was usually based solely on the plant species, and the actual cause is
often something else entirely. As far as I can see, the symptoms are
very similar, and there are probably several other fungi that also
produce similar symptoms. Diagnosing such things reliably needs a
good laboratory and costs a lot of money.

From our point of view, it really doesn't make much difference!


Regards,
Nick Maclaren.

On 24/01/2014 23:12, Nick Maclaren wrote:
In article ,
Spider wrote:

When my tree was affected the local tree surgeon said it was
Phytophthora, but I confess there are elements of Verticillium, too.
It's my bedtime now, so too late to look up verticillium images.
I'm still inclined to blame the very wet winters we've all had, and that
seems to be how Phytophthora works, as I understand it, but I don't rule
out Verticillium now that you come to mention it. More research is
required ... or another urgler.

It wouldn't surprise me if a diagnosis of Phytophthora or Verticillium
was usually based solely on the plant species, and the actual cause is
often something else entirely. As far as I can see, the symptoms are
very similar, and there are probably several other fungi that also
produce similar symptoms. Diagnosing such things reliably needs a
good laboratory and costs a lot of money.

From our point of view, it really doesn't make much difference!


Regards,
Nick Maclaren.




All true. You could always send your pics and perhaps a sample to the
labs at RHS Wisley, who do have that good laboratory and the experts to
use them.

--
Spider.
On high ground in SE London
gardening on heavy clay