Reports & Publications

Secondary Pests Caused by Flooding

Many insects and fungi that affect trees after a flood event are secondary. The primary cause for tree decline before and after the water recedes will be the water itself depriving the roots and/or stem of oxygen.

The trees in and along flooded areas will be stressed and vulnerable. Most of the insects and diseases that show up on the trees will not be the main cause for tree decline. The insects and diseases that appear, generally, will not kill a healthy tree. The water itself will cause significant mortality in yard trees and trees in natural areas before and after the water recedes.

Wood boring insects will be some of the most visual with sawdust or “frass” around the trunk of the tree or in bark crevasses. Most of the exit holes will be visual on the stem of the tree. The larvae of these insects will excavate into the sapwood and structurally weaken the tree.

Bark beetles will be some of the least visible until the damage is done. Boring dust will be present in bark crevasses. They will generally attack the smaller diameter areas of the tree causing mortality of individual branches and the tops.

Several fungi may affect these trees. These fungi can cause the tree to decline and die by infecting the stem or roots.

If you notice any of the aforementioned issues, you should contact your local division forester.

Tree Fungi


Common Secondary Pests

Pest/fungi: Wood Borers

  • Most western conifers and hardwoods
  • Conifers including: pine, spruce, juniper, and cedar
  • Hardwoods including: aspen, oak, elm, maple, willow, black locust, box elder, sycamore, ash and cottonwood

Pest/fungi: Fungi
Host: Most western conifers and hardwoods

Pest/fungi: Armillaria Root Disease
Host: Most hardwoods and conifers
Sign: Mushrooms around base of tree

Pest/fungi: White Mottled Rot
Host: Aspens
Sign: Large white conk at base of trees

Pest/fungi: Aspen Trunk Rot
Host: Aspens
Sign: Black, cracked topped conk on stem

Pest/fungi: Stem Decay-Hardwoods
Host: Birch, ash, black walnut, poplars, buckthorn, willows and many others
Sign: Conks

*Information taken from the USDA Forest Service? 2010 Field Guide to Diseases & Insects of the Rocky Mountain Region.