Most of the year it’s
important to look out for the signs of pests, diseases and fungi that will
weaken the trees in your garden, so we’ve put together a quick guide on what to
watch out for and when to call in your trusted local tree surgeon or arborist.
This is by no means an
exhaustive list, but it contains most of the main ones you might find.
Bugs, beetles and borers
are the main problem pests in the UK. They cause damage to trees through their
diets and reproductive activities and while some cause purely aesthetic issues,
others can be far more damaging.
spruce bark beetle
this pest has only been found in Kent, but it could pop up anywhere, so watch
out for them. If you notice 2cm to 2.5cm holes in the bark and sawdust under
branches or trunks, this is the sign of an insect infestation. These particular
bugs are around 5mm long, shaped like a cylinder, dark brown/black, and shiny
with little brown hairs. They are partial to spruce or pine trees. They bore
into the tree and create chambers into which the larvae are placed – these
chambers become wider as the larvae grow and can damage the tree’s water
transport system, causing dieback.
aptly named pest lays its eggs on the edge of the elm leaves and when the
larvae emerges it munches its away along leaves in a zigzag pattern.
Populations of the elm zig-zag sawfly can explode rapidly, causing a
significant number of leaves to be consumed and weakening the tree as this
happens year after year.
see 2cm to 3.5cm holes and sawdust-like material at the base of the tree and
white, purple or brown resin oozing from these holes as the tree protects
itself from the infestation, then you may have a beetle problem. These
amber/brown bugs are 6–8mm long and around half as wide. Much like other bugs,
it’s the damage they do with their burrowing that can kill a tree, because as
their chambers and tunnels criss-cross inside the trunk they can cut off
circulation, causing dieback to anything above.
chestnut leaf miner
little guys leave tracks inside the leaves of their horse chestnut hosts as
their larvae munch away for sustenance. When they grow up they become tiny
brown and white moths, but in their larval stage they range between 0.5mm and
3.5mm in length. If you notice that the leaves on your horse chestnut tree are
going brown and falling before all others around it, then check the leaves for
the tracks of the miner.
name suggests, in April and May, the caterpillars of this moth march nose to
tail around and up the trunk of the trees in a rippling furry train. Their
nests are located on trunks and made from white silken webbing that goes brown
with age. The danger to trees is the stripping of leaves as the hungry
procession makes it way up and down the tree.
chestnut gall wasp
looks little like an odd fruit growth at the base of a leaf or a leaf stalk, a
bulbous inflation. They start off green or pink and go browner throughout the
summertime. The galls are caused by the wasp larvae and can cause leaves to die
and drop prematurely.
Diseases and fungi
Fungal infections are
especially difficult to irradiate as the fungus often survives the winter in
leaf litter and lets fly its offspring as thousands of spores on the wind
throughout the summer months. Spores can travel many miles on the breeze before
landing on leaves and starting the damage they will cause.
This is a
national problem and really dangerous for ash trees. Caused by fungal
infection, it can be recognised by dark patches on leaves in summer, wilted and
blackened leaves shed in early autumn, and diamond-shaped dark brown lesions
where branches meet trunk. Ash dieback is often fatal for the tree as the fungal
growth blocks the flow of water around the tree.
fungal infection affects pine trees and can cause needles to turn reddish-brown
or brown with yellow spots and fall from the tree, leaving a telltale ‘lion’s tail’
effect with just the needles on the end of branches left. All this
discolouration and needle shedding will weaken the tree’s ability to photosynthesize.
fungus that causes this disease is called Ophiostoma novo-ulmi and like other fungal
infections will cause leaves to yellow and fall early, but this one also causes
the twigs of the tree to bend down in what’s known as a ‘shepherd’s crook’.
This fungus is often introduced to the tree by feeding elm bark beetles and
once established will release toxins that impede the tree’s ability to
transport water around its system, causing extensive dieback.
chestnut bleeding canker
notice cracks in the bark which ooze a reddish-brown liquid in the summertime
then your tree could have been infected by a bacterial pathogen which
multiplies and blocks the tree’s water transport system. Often this is nothing
to worry about, but if the cankers grow and spread across the tree then this
can cause serious problems.
If you have noticed any of
these signs on your garden trees, then call in the experts. The longer you
leave things, the more your trees – and those of your neighbours – could be
impacted and the problem will become much more serious.
To book a survey and consultation with one of our ARB Approved arborists for
advice on your trees or to book our tree surgeons to prune/maintain or fell
your tree(s), call us on 0208 292 8992.