Controlling Bark Borers
The most common causes of death for newly planted trees are drowning and planting too deep, but the third most common hazard is bark borer beetles and their larvae, borer worms. These three problems are related, because borers seek out trees that are under stress. Planting too deep or in poorly drained soil, and/or over-watering, are frequent causes of stress.
Plants under stress, and damaged or torn bark, give off ethanol or pheromones, which attract bark borer beetles. The beetles drill into the outer bark, or enter torn areas, and lay their eggs. The eggs hatch little borer worms, which then tunnel inside the inner bark, eating as they move around, and replacing the healthy inner bark with sawdust.
The green inner bark of trees, called cambium, is the pipeline for transporting food and water up and down the tree trunk. Damage to the cambium layer stops this life-giving flow, causing loss of limbs higher up in the tree, and killing the protective outer bark. This is first visible as a swelling on the tree trunk, and later the bark begins to peel.
Trees with soft outer bark, particularly dogwoods and young maples, are especially vulnerable to bark borer damage. So are trees with torn or damaged bark, or stubs caused by improper pruning cuts. Anywhere that the green cambium is exposed, insect pests will take advantage and set up housekeeping inside your tree. This is one reason we treat tree wounds with special paint called tree wound dressing. This paint protects the exposed cambium and also slows the release of ethanol and pheromones.
There are many different types of burrowing beetles. The most common are flat-headed wood borers, commonly called jewel beetles. They attack recently moved trees or ones that are stressed. Arborists and tree surgeons can treat borer infestations with insecticide spray. For homeowners, we believe that the most effective, easiest way is “systemic drench”, using imidacloprid insecticide.
Imidacloprid is available in concentrated products like Bonide’s “12 month Tree & Shrub Insect Control” or “Ferti-lome Tree & Shrub Drench”. Following label directions, mix the concentrate in a bucket of water and slowly pour it around the base of the tree, so it soaks right in. The tree will absorb the insecticide and transport it inside the inner bark, where it poisons borer larvae.
You can help avoid bark borer damage by keeping your tree healthy and strong. Regular feeding helps a lot. Maintaining mulch circles around the tree helps also, by preventing bark damage from mowers and trimmers, eliminating competition from lawn grass roots, and retaining moisture. Proper pruning and transplant practices are important, too.
Watch newly-planted trees closely, checking for bark swelling or peeling on the trunk. You can save your tree by acting quickly. If you wait too long, borers will encircle the entire trunk, destroying the inner bark and killing the tree. It’s a good idea to treat newly planted dogwoods, maples and other smooth-barked trees shortly after planting, just in case borers have already drilled into the soft bark and laid their eggs. Prevention is the best therapy.
Steve Boehme is a landscape designer/installer specializing in landscape “makeovers”. “Let’s Grow” is published weekly; column archives are online at www.goodseedfarm.com. For more information call GoodSeed Farm Landscapes at (937) 587-7021. formation is available online at www.goodseedfarm.com or call (937) 587-7021.