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Hertfordshire County Council

Pests and diseases affecting Hertfordshire

The Forestry Commission explains how to recognise them, how to report them and what other action to take:

A fungal disease that kills ash trees through leaf loss, crown dieback and bark lesions.

Its caterpillars strip the leaves from oak trees and their hairs cause rashes and allergic reactions for people and animals.

Affected trees have dark fluid oozing from cracks in the bark and will die within 4-5 years.

Causes bark cracks and cankers, as well as bleeding from from the trunk and branches.

This insect's larvae damages leaves, so they discolour and fall before autumn.

The wasp's larvae cause growths called 'galls' on a tree's leaves, as well as their buds and stalks.

How you can help

  • When buying plants and trees, try to choose native species and check that they were sourced and grown in the UK.
  • Look out for signs of pests and disease. If you think a tree is infected, report it to the Forestry Commission and check their advice before taking any action yourself.
  • Avoid pruning or cutting down affected trees and check they're not protected by a district council tree preservation order. If you're felling large trees, or several at once, you might need a felling licence.
  • If you find a case of ash dieback on land that you own or manage, follow the guidance in our chalara action toolkit.

What we're doing to help

  • There are around 150,000 trees on council-owned highways. We monitor them for signs of ash dieback and will manage it where it's found, removing the tree if necessary.
  • To reduce the impact of ash dieback, we have stopped planting ash trees and are instead planting other local species in ash woodland.
  • Our volunteers have been working to control the damage caused by ash dieback since 2012.
  • Take a look at our tree health report for more information.