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Elm Bark Beetles

The elm bark beetle (not to be confused with the Elm Leaf Beetle) is by far the most important factor in the spread of Dutch Elm Disease (DED).

These tiny insects’ lives revolve around elm trees. The female beetle tunnels into the tree between the bark and the wood to lay its eggs. When the eggs hatch, the larvae tunnel farther into the tree, to feed before emerging as mature beetles. 

Adults feed in the crown of the tree, moving from tree to tree before breeding again.

If a beetle breeds or feeds in a DED-infected tree, the sticky spores of the fungus become attached to its back. When the beetle moves to a healthy tree, so do the spores.

There are two species of the elm bark beetle in North America – the European and the Native elm bark beetles. The European is more sensitive to temperature and lives mainly in southern regions. The Native is dominant in the mid-west.

The native elm bark beetle consists of two separate breeding groups. One group over-winters as larvae in the breeding tunnels, while the second group over-winters as adults. These adults emerge from mid-April to mid-May. It is their feeding phase that causes the majority of DED infections. It is believed that the European elm bark beetle over-winters as larvae.

Recommended Steps to Control Elm Bark Beetles

If caught early enough, immediately apply the Multi-Insect Killer Tree Injection Kit treatment to the tree. This insecticide is injected directly into the tree’s vascular system and released quickly to help control insects already inside the vascular system.

To prevent repeated Elm bark beetles, as well as in areas of known Elm Bark beetle activity, a number of steps can be taken to prevent attacks in healthy trees. In the early spring, treating the tree with the Once-A-Year Insecticidal Drench w/Merit helps protect the tree’s vascular system. This treatment can be supplemented by regularly sprayingthe tree’s trunk with a good dosage of Borer-Miner Killer (every three to three weeks), thus creating a barrier to reduce further insect penetration through the bark.

The good news is that healthy, well-situated, well-maintained, and healthy trees are normally more resistant to the borer, so they’re less of a target. Trees under stress are more likely to be targets of the Elm Bark Beetle, so it is important to ensure that elm trees receive adequate water. To help ensure that a tree is healthy, apply a TreeHelp Annual Care Kit for Elm in the spring or early summer which contain the appropriate fertilizer and mycorrhizal treatment to support the proper functioning og the root system.