01/09/2026
“What my cotton woods are hollow inside, how? It’s standing tall and strong hasn't lost any large branches yet it doesn’t need anything done to it” — We see this way to often large Cottonwood and Ash trees with a large cavity in the tree that you don’t know is their but we do and we can prevent this before it happens to your tree with the right treatment program in place executed by our export arborist team here at Greenleaf. This Cottonwood we got to before it was too late, don’t wait until it’s too late for your tree.
Circled in the first picture are two insect species we found side by side under the bark during a wedge cut. Both insects can cause large cavities in trees throughout their life cycle and without you knowing it until it is too late.
The legless, creamy-white grubs with brownish heads you see on the top right is called (Plectrodera Scalaton), also known as a Cottonwood Borer. In their mature form, they are a bold black and white spotted beetle with long black antennae often exceeding the length of their body found primarily east of the Rocky Mountains. Adult female Cottonwood Borers lay eggs in pits that are chewed into the base of the tree by the females. After two weeks, larvae hatch and feed on phloem within the root collar of the tree. They damage Cottonwood Trees primarily through larval tunneling in the trunk and roots. The third photo we have posted here shows a good cross-sectional view of what their tunneling passageways look like at the base of a tree, causing significant structural damage, girdling or hollowing out the heartwood, sapwood, and roots. Toward the end of their larvae stage, taking up to two years to mature, they begin pupating in the roots for three weeks, adults emerge and tunnel their way to the surface during late spring to midsummer, living up to one month. Adult feeding can damage shoots, causing them to blacken, shrivel and die. This damage is usually not extensive and does not pose a serious threat to trees compared to the larva damage that is present in this tree.
The insect circled to the bottom left of the first photo, living beside the Cottonwood Boar is called (Cucujus clavipes), also commonly known as a Flat Bark Beetle in its larvae stage, it is actually a beneficial insect. This beetles larvae lives under the bark in dead or dying trees often Elm, Poplar, or Ash Trees where they are predatory, eating other wood-boring beetle larvae and mites, making them Mother Nature's natural beneficial pest control. The Flat Bark Beetle are a unique insect as their eggs are laid in crevices of the bark, hatching into C-shaped larvae creating galleries as they feed on other small arthropods (like other beetle larvae) and fungi. They are flat, legless grubs almost translucent dark red in color that grow significantly, often over two winters, developing through several instars and often overwintering before pupating and emerging as adults in spring/summer, known for their unique antifreeze abilities to survive extreme cold. Adults emerge from pupae, typically in late summer or fall, and overwinter under the bark, becoming active and mating in spring/summer when they are found on tree surfaces.
Knowing and understanding what these two different insects life cycles and rolls in the ecosystem as well as the vast variety of other insects life cycles and rolls, and how they work inside of our landscapes are crucial tools for us as arborists to utilize to better help our customers make educated decisions to properly mitigate a tree from causing potential damage to your properties or someone nearby in a structural tree failure before its to late. This tree you see was a culprit of structural failure in a large wind storm our are received. Strong winds toppled almost 70% of the tree on itself damaging fencing and other near by trees as it fell. Stay ahead of this risk by getting our arborist involved in your tree health plan in the early stages of the trees development and remain consistent with a seasonal fungicide, insecticide, and fertilizer application to prevent insect or fungi damage all together. If you suspect boar damage is already present in your trees be sure to schedule with our arborist to come out and give you an in-depth analysis of your trees current condition and develop a tree health care plan for you, because the value of a tree is more than just a tree.
