6 Common Tree Pests and How to Manage Them

New and invasive pests can pose a serious risk to trees, crops, and plants in the UK. You might think this only applies to forests and farms, but trees on your own property are far from immune.

What can you do about tree pests, though, and how can you identify them when they make their way into your garden? Luckily, we are here to help you out.

Read on to learn all about ten different tree pests along with symptoms, treatments, and how you can prevent them from coming back.

1. Horse Chestnut Leaf-Miner

The Horse Chestnut Leaf-Miner is a breed of moth caterpillar and was first found in England in 2002. The caterpillars feed by tunnelling (or “mining”) through leaves and eating the contents between the two outermost layers of the leaf.

This is also where they live and lay eggs. Females lay eggs between May and August, leaving behind anywhere from 20 to 40 at a time. The eggs can take two to three weeks to hatch, and that is typically when the larvae will feed, leaving behind brown patches.

They live out their life cycle inside the host leaves until it is time to move on and lay more eggs.

Overpopulation can occur, but it does not have to reach that stage before you can take steps towards pest control. Typically, clearing leaves as they fall from trees is enough, but remember to burn the leaves as you rake them up. In most cases, pesticides are not necessary to get rid of these bugs.

2. Citrus Longhorn Beetle

This is an invasive species that is found in broadleaf trees and shrub species throughout the world. They are originally from Asia, but as trees have been exported out of that regional area, the spread of Citrus Long-Horned Beetles has become increasingly common.

They are not common in the UK, but there have been individual interceptions since 2005 and they are still something to be on the lookout for — especially if you have trees exported for any reason.

Breakouts are most likely to occur between May and July, and symptoms typically include round holes on the trunk of a tree and exposed roots.

3. Tortrix Moth

Out of the over 400 species of roller moth in the UK, only two of them actually cause major problems for plants and trees. It is a native species that enjoy feeding on new, tender leaves, and if left heavily infested in trees, it can lead to complete defoliation, which can affect the tree’s ability to photosynthesise.

They are called roller moths because they roll the leaf edges around themselves as they pupate — something to look out for. Other signs include seeing eggs on the tree.

4. Silver or Downy Birch Borer

Though bronze birch borers are a frequent problem in North America, the UK-native silver and/or downy birch borer can wreak havoc as well. These tree insects tend to live in trees that have already been weakened by drought, old age, defoliation, or even soil compaction.

They are small, narrow, metallic-coloured beetles that burrow into the trunks of birch trees and leave by leaf yellowing and branch dieback. You may even notice burrows throughout the trunk, or three- to five-millimetre-wide holes where the beetle exited from.

5. Elm Zigzag Sawfly

This insect targets elm trees, feeding upon the leaves, which can lead to defoliation when they are left to their own devices. The insect gets its name from the zigzag patterns that it leaves as it feeds on leaves.

These tree bugs are originally from southeast Asia, but they are commonly found in the southeast and east midlands of England, though it is possible that it could spread farther.

When they feed, they are going to typically start from the outside of the leaf and work their way in. That is why the easiest identification is going to be looking for the zigzag pattern they leave behind. When fully grown, it’s hard for them to be seen or spotted, so you might need the help of a professional.

If you suspect these pests, it is best to check multiple spots when you are searching for them, as they are likely to spread out among multiple leaves at a time.

6. Green Spruce Aphid

This pest is native to continental Europe, but it has been found in the UK, North America, New Zealand, Australia, and Chile. These pests exclusively target spruce trees, though it’s been found on some species of fir and other conifer trees.

Though their presence does not cause a lot of defoliation, it can lead to a significant loss of needles, which can affect a tree’s overall growth rates. It can also leave it susceptible to other diseases, or even bacterial and fungal attacks.

To identify green aphids, you typically look to the needles. Older needles are going to develop pale, mottled yellow discolouration during late winter early spring. Trees will also begin losing needles, and there will be a significant difference between old, infected shoots and new shoots that have grown out of the tree.

If green shoots are still growing, then saving the tree is still possible.

Chemical prevention for these garden pests is not really recommended. The best way that experts have found to treat them is by spreading natural predators in areas they are common.

Have You Experienced Any of These Common Tree Pests?

Now that we have gone over six of the most common tree pests and the traces they leave behind, you may have noticed that you have experienced some of these pests before without even realizing it. If you have in the past, then you might know how to deal with them.

However, if these pests are new to you, you might need to consult with an expert. At GraftinGardeners, we are specialists in tree surveys, and pest and disease diagnosis and control. If pests have affected your trees, don’t worry — we are here to help. We can provide comprehensive assessments and tailor effective strategies to safeguard your trees against further damage.

If you’re ready to protect your trees and ensure their health, please don’t hesitate to contact us today to get started on safeguarding your trees against further damage.