The Beetles’ Bite is Worse Than Its Bark!

White Ash Tree attacked by Bark Beetles.

by Bonnie Corwin

As if the long drought over the last several years wasn’t enough to bug you, then reading this should take care of it. This little tiny beetle the size of a rice grain is responsible for killing over 102 million trees in the state of California since 2010, per the U.S. Forest Service. They are infecting the entire Western United States.

How does this affect us? Remember that firestorm that happened just last month? Between the drought and these pesky bugs, we are in even more danger from wildfire than before. Since the trees are dry and then dying, this contributes to the danger of fire burning too close to our homes. This danger is even higher due to the bark beetle.

Dead, beetle-killed wood is a heavy fuel. Once it is ignited, it burns hot! But make no mistake. More trees die from bark beetle than wildfire. When there is drought, the bark beetle can kill trees of all ages. Group killing of trees is also common.

The saddest part about this is the number of trees that are expected to die in Southern California’s most populated regions due to the drought weakening our trees. Trees have their very own self-defense against the bark beetle, but not when they are not healthy.

How do bark beetles go from one tree to another? They fly. They can fly up to two miles. They search out a suitable host tree close by, rather than fly long distances. Bark beetles emit an aggregation phenome to attract other beetles. After there are enough of the beetles, then the beetles emit an anti-aggregation phenome, signaling other beetles to move on to another tree.

As if there wasn’t enough to do on your property, now add in regular tree inspections. First, check the bark of your tree. The tree has its own defense mechanism. It releases a pitch against a beetle attack. If you see a white pitch tube about half an inch to three-quarters of an inch filled with a substance that looks like sap, it means that the tree was successful at defending itself against the bark beetle. If the pitch is reddish-brown, however, the bark beetle successfully invaded the tree. If you see woodpeckers foraging, it probably means that bark beetles are present.

Do you have pine trees? If the needles begin to turn a reddish-brown color, beginning oftentimes at the top of the tree and moving down, there may be an infestation. Some trees may change color slowly from green to brown. Others, may die within a few weeks. Some types of trees survive years before they die. If your tree appears dead, it’s often too late.

You might be thinking by now that you need to identify the trees on your property and see if they are susceptible to the bark beetle. Once determined that you have trees that might attract the bark beetle and you then determine that the tree is not infested, take action to keep it that way. Drought is one of the ways the trees are really stressed. We have had our share of drought.

Typically bark beetles are “secondary colonizers.” They will attack trees that are already stressed due to drought, root damage from nearby construction activity, excessive pruning of live wood on the tree, or other tree pests and diseases. There are several different treatment options, but remember if there is already an infestation, you cannot help that particular tree. The best management practice is one of prevention: apply adequate supplemental irrigation in times of drought, apply mulch, avoid damaging the roots, and minimize livewood pruning as much as possible.

For irrigation, think “long and deep.” Typical turfgrass irrigation of several minutes a few times per week does not provide substantial irrigation to mature trees. Apply irrigation at a slow application rate for several hours at a time (as much as 24 hours at a time, depending on the soil conditions) 2-4 times per MONTH. The goal is to moisten the soil to a depth of 6-12 inches per irrigation and to then let the soil dry out completely. Check with a Certified Arborist for the species-specific irrigation needs of your trees.

Another preventative measure homeowners can take is to allow needle drop to accumulate over the root zone of your trees. This forms an insulating layer of mulch that reduces the rate of water loss due to evaporation and keeps roots cool in hot summer temperatures. Creating an environment that is favorable to tree roots reduces the likelihood of an infestation of bark beetles.

Before asking a tree service to prune your trees, remember that leaves and needles are the production sites of food for the tree. The process of photosynthesis runs a “pump” that draws water up the stem. When too much live foliage is removed from a tree, the sap pressure along the stem is reduced. Trees with low sap pressure are less able to “pitch out” invading beetles. Retaining more foliage gives the trees a better chance of defending themselves. A certified arborist can help you balance tree health with your pruning objectives.

If your tress are regularly monitored, and you catch an infestation early enough, chemical treatment may help, otherwise it is ineffective and too late. So if you are going to have an arborist or tree surgeon help you, learn as much as you can to determine if a chemical treatment will actually do any good.

For more information or how to care for your trees, you can call Board Certified Master Arborist James Komen at (818) 495-5344. If you have already determined that your tree is infected, you can call Tree Surgeon Devin Petricca at 747- 206-6197.

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