Have you ever looked at your tree and thought, “Why are the leaves turning brown?” or “Why is the bark peeling?” Maybe it’s dropping leaves in summer, or you’ve spotted something strange growing on it.
Just like people, trees can get sick too. And here in the UK, we see many diseases and pests that can harm or even kill trees. Some problems are easy to spot and fix, but others can be serious if left untreated.
At Leicester Tree Services, we’ve spent years caring for trees across the city and surrounding areas. We’ve seen all kinds of problems, from fungal infections to tiny insects that cause big damage. In this guide, we’ll share the most common tree diseases and pests in the UK, how to spot them, and what to do if you’re worried.
Common Tree Diseases in the UK
Tree diseases are usually caused by fungi, bacteria, or viruses. They can attack the leaves, bark, branches, or roots. Some diseases move slowly and only affect one tree, while others spread quickly and harm many trees in one area.
Here are some of the most common tree diseases we see in Leicester.
1. Ash Dieback (Hymenoscyphus fraxineus)
Ash Dieback is a very serious disease. It affects ash trees and has killed millions across the UK. You may notice dead branches high in the tree, black spots on the leaves or stems, pale cracks in the bark, or thinning leaves in the canopy.
It weakens the tree over time and makes it dangerous, especially in public places or near buildings. If left untreated, the tree may die completely. If you suspect Ash Dieback, it’s best to have the tree checked by a professional. In many cases, it may need to be removed for safety reasons.
2. Dutch Elm Disease (Ophiostoma fungi)
This well-known disease wiped out many of the UK’s elm trees in the past. It is spread by bark beetles and works quickly.
Signs to look for include leaves turning yellow or brown early in the year, branches dying from the top down, peeling bark, and curling leaves. If a tree is infected, it usually cannot be saved. Removing it helps stop the spread to nearby elms.
3. Horse Chestnut Leaf Blotch (Guignardia aesculi)
This disease affects horse chestnut trees—the ones we get conkers from. It causes brown spots on leaves, often in summer. By late summer, the leaves may turn early and fall off.
Although it looks unpleasant, this disease doesn’t usually kill the tree. It can, however, weaken it over time. Raking and removing fallen leaves each autumn can help stop the disease from coming back the next year.
4. Honey Fungus (Armillaria)
This is one of the most harmful fungal diseases for trees and woody plants. It lives underground and attacks the roots, often killing the tree from below.
Signs include white fungus under the bark, mushrooms at the base in autumn, yellowing or wilting leaves, and sudden death of branches. Unfortunately, there is no cure for honey fungus. Trees with it often need to be removed completely.
5. Powdery Mildew
Powdery mildew is a common fungal disease that shows up in dry, warm weather. It causes a white or grey powder to appear on leaves, especially on oaks, sycamores, and fruit trees. Leaves may also curl or twist.
It’s not deadly, but it can slow down growth. Improving airflow around the tree and giving it extra water can help reduce the impact.
Pests That Damage Trees
Pests are insects or bugs that feed on trees. Some chew leaves, while others suck sap or bore into the bark. In large numbers, pests can cause serious damage.
Here are some pests we see most often in the UK.
1. Aphids (Greenfly / Blackfly)
Aphids are small bugs that suck sap from the tree’s leaves and stems. You’ll often see sticky patches called honeydew, and maybe black mould growing on that sticky area. Leaves may curl or turn yellow.
They usually aren’t a serious problem in small numbers, and ladybirds help eat them. But in large groups, they can weaken the tree, and we may suggest treatments that are safe for trees and the environment.
2. Oak Processionary Moth (OPM)
This pest is becoming more common, especially in southern England. The caterpillars of the oak processionary moth feed on oak leaves and move in long, straight lines—like a procession.
They also build silky white nests on tree trunks and branches. These caterpillars can be dangerous to people and pets, causing skin rashes and breathing problems. Never touch them. If you spot them, contact a tree specialist trained to deal with OPM.
3. Leaf Miners
Leaf miners are tiny insects that live inside tree leaves and eat the soft parts. On horse chestnut trees, they leave brown lines or blotches. Trees may drop leaves early.
While the damage usually looks worse than it is, repeated attacks can weaken a tree. Removing fallen leaves in autumn can reduce the number of pests next year.
4. Scale Insects
Scale insects look like tiny bumps on branches or stems. They suck sap and can lead to sticky honeydew and black mould on leaves.
They don’t usually move and are often mistaken for growths on the bark. Mild infestations aren’t serious, but heavy ones may require treatment.
5. Asian Longhorn Beetle (Rare but Serious)
This beetle is not common in the UK but is considered a serious threat. It attacks maple, birch, poplar, and willow trees. It bores large holes in the trunk and branches.
If you see round holes with sawdust at the base of a tree, report it to the Forestry Commission immediately. Trees with this beetle usually have to be removed to stop it from spreading.
How We Can Help
If you think your tree is sick or being attacked by pests, don’t wait. Some issues, like honey fungus or Ash Dieback, can make a tree unsafe. Dead or dying branches can fall and cause damage.
At Leicester Tree Services, we offer full tree inspections. We’ll check for diseases, pests, and structural damage. We give honest advice and always put safety first.
If treatment is possible, we’ll recommend the best solution. If the tree is too far gone, we can safely remove it and grind the stump. We’re fully trained, insured, and local.
How to Help Your Trees Stay Healthy
There are things you can do at home to support your trees and reduce the risk of pests and diseases:
Check trees regularly – Look at the bark, branches, and leaves every season.
Remove fallen leaves – Many fungi and insects live in old leaves.
Water during dry weather – Especially for young or newly planted trees.
Avoid damaging roots – Don’t park cars or dig too close to trees.
Prune correctly – Don’t cut too much or too often.
Call us if unsure – We’re always happy to give advice.
Let’s Keep Leicester’s Trees Strong
Our trees are a big part of our homes, streets, and parks. They give us shade, clean air, and beauty. But they also need care—especially when facing disease or pests.
If you’ve seen something odd on your tree, or just want a health check, give us a call. At Leicester Tree Services, we’re proud to protect Leicester’s trees and the people who live around them.
✅ Local and friendly
✅ Fully qualified and insured
✅ Honest advice and expert service
✅ Serving homes, businesses, and councils across Leicestershire
Call us today for a tree inspection or advice. Together, we can keep our trees healthy, safe, and standing strong.