"Emery Davis" wrote in message
...
On Fri, 17 Apr 2015 19:43:37 +0100, FrankB wrote:

I have a Japanese Maple which has been healthy throughout last year. But
this spring it became noticeable that a number of new top stems have
died back. I've now cut these back to main branches. I've no idea what
killed them and we haven't had that cold a winter to cause that amount
of dieback.
New growth has already started lower down the main stem, and at the
moment that looks healthy and vigorous. But I'm wondering whether the
symptoms could be early signs of verticillium wilt although there's no
sign of the new growth wilting so far?

I don't know much about Japanese Maples but recently learned that vw is
the main threat to growing them successfully.

Verticillium wilt usually happens in spring or summer depending on form:
the sudden spring wilt and death characterised by a loss of turgidity in
new growth is caused by albo-atrum IIRC, the more common long term
verticillium -- that we sometimes call the cancer of maples -- dahliae
occurs more during summer, and can be controlled by cutting back, at
least for a while. I have certainly tens of maples that suffer from this
form but survive or even thrive to some extent.

In all likelyhood what you're seeing is pseudomonas infections which is
the most common cause of winter tip dieback in maples. The bacteria
enters the soft tissue when temperatures are near freezing and causes
blackening and stem death. Sometimes lesions appear further down the
stem, often they are round but always with the characteristic blackening.

In contrast to verticillium, pseudomonas can be controlled by copper,
e.g. bordeaux mix or some other pulverized on the stems. The treatment
should be repeated every 7-14 days until all of the blackening is gone;
but of course cutting the blackened parts off is the right thing to do
once the threat of frost is over, and the copper becomes mostly
prophylactic.

Risk of pseudomonas is a main reason why only light fertilization of
maples is usually recommended.

HTH,

Thanks for that. I think Bordeaux mixture is no longer available at garden
centres in the UK sonce the EU were considering banning it 2 years ago. I
haven't seen any bottles of it around of late.

By coincidence someone else has just posted on a forum with the identical
problem to mine.

http://www.growsonyou.com/question/show/287153