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Bark Beetles

Summary: Bark beetles are difficult to manage with pesticide treatments. Good cultural practices such as pruning and timely watering seem to offer the best methods of control of bark beetles .

With over 600 species of bark beetles, the good news is bark beetles do not usually kill healthy trees. The 5mm insects tend to attack trees that are already under environmental stress caused by drought, infection or old age or recently transplanted trees. The bad news is, if a healthy tree becomes infested there is little to do except cut off affected limbs.

Bark beetles, of which there are many varieties, damage trees by burrowing under the bark to feed on the inner layer of wood and to lay eggs. When the eggs hatch the bark beetle larvae digs tunnels into the wood beneath the bark. The beetle develops from the larva into a pupa and finally into an adult before it leaves the chamber and flies to another tree to start the cycle over again.

Bark beetles have several generations each year. You can take measures to protect trees by knowing what kind of beetle is infesting trees in your area and when they are flying.  The type of tree species attacked will help distinguish the kind of beetle you are battling.

On the positive side, bark beetles are ecologically helpful because they feed on dead wood to assist in decomposition. They also benefit the overall health of a forest because they feed on already weakened trees and help make room for new, healthy trees. Healthy trees repel bark beetles by leaking sap that contains insecticidal chemicals driving off burrowing beetles. However, large outbreaks of bark beetles can overwhelm even healthy trees.

In recent years bark beetles have been spreading through British Columbia because there has not been enough freezing weather to reduce their population. Researchers fear global climate change might create a growing bark beetle population problem, a potential disaster for the lumber industry.

If the bark beetle's burrowing was not bad enough, they also carry fungal spores that can infect trees. Dutch Elm disease, for example, is spread by Elm bark beetles and can easily kill a healthy tree, sometimes in as little as two months. The disease is spread when the beetles emerge as adults from an infected tree and carry the spores to a new tree by burrowing into it. The fungus actually helps the beetle by slowing the flow of tree sap, but the spores interfere with the distribution of water and nutrients clogging up the tree's interior system.

There are ongoing forest management efforts by the US Forest Service and state agencies to save bark beetle infested trees and forests. Infested trees are marked and removed. Root connections are severed to help save trees from spreading fungi. Pruning dead branches or branches where bark beetle larvae have begun burrowing can help save a healthier tree. 

Insecticides do not kill the bark beetle larvae tunneling beneath the bark. If pesticides are used, the bark must be sprayed so that adult bark beetles are killed as they attempt to bore into the bark to lay eggs. Sprays wear off in the rain in sun, so fresh treatments are required. Plus, treating badly infested trees will have no effect at all, but may kill beneficial insects. Improving the overall health of a tree by giving plenty of water in the summer and by pruning dead branches will often be enough to prevent a bark beetle predicament.

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