Trees, like people, can suffer from many ailments. Some
can be terminal, others may disfigure, and some will be
short term.
In recent years, Horse Chestnuts (Aesculus sp.) have
been suffering from a number of different problems that
have given their owners great cause for concern.
Some of the problems are well known, and not restricted
to Horse Chestnuts, such as Honey Fungus (Armillaria
sp.). We must also remember that trees, like people, grow
old and will eventually die. There are, however, three
particular problems that have recently become more
noticeable:
Leaf Blotch (Guinardia aesculi): this is a fungus, which
causes large chestnut-red or dull brown, irregular
blotches to be seen on the leaves, from mid summer.
These are often concentrated at the tips and margins of
the leaves, and are often outlined by a conspicuous
yellow band. Severely browned leaves are rolled upwards
longitudinally, and whole leaves fall prematurely.
The effects may be considered unsightly, but as the
damage occurs after most growth has taken place, it has
little effect on the general health of the tree. It is often
mistaken for early autumn onset, but autumn colour
changes are fairly uniform, not irregularly blotchy. It is
commonly found on most varieties of Horse Chestnut in
this country.
There are no specific controls available, but it is believed
that the fungus over-winters on fallen leaves, and
develops in the spring to infect new leaves. Raking up,
and disposing of fallen leaves may, therefore, be helpful.
Bleeding Canker (Phytopthera cactorum and P.
citricola): these are fungi most commonly seen on Horse
Chestnut, Birch, and occasionally Lime. There appears,
however, to be no reason why they could not be seen on
a number of other species of tree.
The fungi are confined to the bark of the tree, and grow through it
to kill the phloem and cambium layers beneath.
It does not seem to require an injury to the bark for
the fungi to become established. The fungi also cause
Phytopthera root disease, so it is probable that they are
resident in the soil, or on the roots of other plants in the
area.
Infection is recognised by scattered drops of rusty-red,
yellow-brown, or almost black, gummy liquid ooze from
patches of bark on the stem or branches of the tree (this
does not contain the fungus). Eventually, limbs may die,
but the weeping is so conspicuous that it is this that will
draw attention to the problem.
An attempt to control the infection can be made by
cutting out all dead and dying bark, and then removing a strip of
healthy bark 2" wide from the periphery of the
wound. The exposed tissue should then be treated with an
approved wound paint containing a fungicide effective
against Phytopthera. (Special care is required to ensure
that the requirements of the Pesticide Regulations are
adhered to). All removed bark should be burnt.
There are currently no known methods of prevention.
Horse Chestnut Leaf Miner (Cameraria ohridella): this
is a moth that can cause severe damage to the foliage of the Horse
Chestnut on an annual basis. The larvae of the moth mine within the
leaves destroying most of the leaf tissues (there can be up to 700 on a
single leaf), and severely damaged leaves shrivel and turn brown early
often
defoliating the tree before normal leaf-fall in the autumn.
The spread is by the flight of adult moths, and through the
passive transportation of the moth or infested leaves on
vehicles, trains etc. The insect over-winters as a pupa in
fallen leaves.
As with Leaf Blotch, the most effective way to apply any
control measures is to rake up fallen leaves and dispose of
them. The commercial composting or burning of the
leaves destroys the pupae, thus reducing the moth
population the following spring. Garden composting is not
adequate, as the heat generated is insufficient to kill the
pupae. Small heaps of leaves can be buried under a layer
of soil to prevent adult emergence the following spring.
The use of insecticides to control the moth is not feasible,
as they would also kill many beneficial insects.
Despite these problems, there is no cause for panic. If the
majority of owners introduce sensible maintenance
measures, we can hopefully keep the problems at a low
level.
MELVYNE CROW
Landscape Services Manager
Braintree District Council
