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  • Callum Ward

How to Identify and Treat Common Tree Pests

tree pests

Trees are essential components of our ecosystems, providing shade, oxygen, and habitat for wildlife. However, they are vulnerable to a variety of tree pests that can cause significant damage. Identifying and treating these pests promptly is crucial for maintaining the health and longevity of your trees. Here’s a comprehensive guide to help you identify and treat common tree pests effectively.

Identifying Common Tree Pests


Aphids are small, soft-bodied insects that feed on tree sap. They can be green, black, brown, or yellow and are often found in clusters on the undersides of leaves. Signs of aphid infestation include yellowing leaves, distorted growth, and the presence of a sticky substance called honeydew, which can lead to sooty mould.


Caterpillars are the larvae of moths and butterflies. They can defoliate trees rapidly, leading to weakened trees and reduced growth. Common types include the tent caterpillar, gypsy moth caterpillar, and the fall webworm. Look for chewed leaves, silk tents in branches, and clusters of caterpillars.

Emerald Ash Borer

The emerald ash borer is a metallic green beetle that specifically targets ash trees. Signs of infestation include D-shaped exit holes in the bark, canopy dieback, and serpentine galleries under the bark. Infested trees often exhibit thinning crowns and increased woodpecker activity.

Scale Insects

Scale insects are tiny, sap-sucking pests that appear as small bumps on tree branches and trunks. They can be white, grey, brown, or black. Symptoms of a scale infestation include yellowing leaves, premature leaf drop, and a general decline in tree health.

Bark Beetles

Bark beetles bore into the bark of trees to lay their eggs. The larvae tunnel through the wood, disrupting nutrient flow and weakening the tree. Signs of infestation include small, round holes in the bark, sawdust-like frass, and dying branches.

Treating Common Tree Pests

Aphid Treatment

To treat aphids, you can start by spraying the tree with a strong jet of water to dislodge the pests. Insecticidal soaps and horticultural oils are effective treatments and are less harmful to beneficial insects. Introducing natural predators, such as ladybirds, can also help control aphid populations.

Caterpillar Treatment

For caterpillar infestations, handpicking and destroying the larvae can be effective for small trees. For larger infestations, biological insecticides containing Bacillus thuringiensis (Bt) are a safe and effective option. Bt specifically targets caterpillars without harming other wildlife.

Emerald Ash Borer Treatment

Emerald ash borer infestations require immediate action. Systemic insecticides can be injected into the tree to kill the larvae. In severe cases, infested trees may need to be removed to prevent the spread of the beetle. Regular monitoring and early detection are crucial for managing this pest.

Scale Insect Treatment

Treating scale insects involves using horticultural oils during the dormant season to smother the pests. For active infestations, systemic insecticides can be effective. Pruning and destroying heavily infested branches can also help manage the population.

Bark Beetle Treatment

Bark beetle infestations are challenging to treat. Preventive measures, such as maintaining tree health through proper watering, mulching, and avoiding mechanical injuries, are essential. Insecticides can be applied to the bark to kill beetles before they bore into the tree. Severely infested trees may need to be removed to prevent further spread.

Preventing Tree Pests

Preventing tree pests is often more effective than treating infestations. Here are some preventive measures:

- Regular Inspections: Conduct regular inspections of your trees to detect early signs of pests.

- Proper Tree Care: Maintain tree health through adequate watering, mulching, and fertilisation.

- Pruning: Prune dead or diseased branches to prevent pest habitats.

- Beneficial Insects: Encourage natural predators by planting diverse vegetation.

- Sanitation: Remove fallen leaves and debris that can harbour pests.

Identifying and treating tree pests promptly is crucial for maintaining healthy trees. Regular inspections, proper tree care, and preventive measures can significantly reduce the risk of pest infestations. When infestations occur, using the appropriate treatments and consulting with a certified arborist can help manage the pests effectively. By staying vigilant and proactive, you can ensure the health and longevity of your trees, keeping your landscape vibrant and thriving, contact us now.

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