Armillaria Root Rot

Armillaria root rot, caused by fungi in the genus Armillaria, affects trees, shrubs, vines and even herbaceous plants throughout the world, in both tropical and temperate climates. These endemic fungi typically act opportunistically, killing weakened trees, and are frequently a sign of natural stand aging and not a serious concern.  However, Armillaria fungi can also infect and kill healthy trees, or make them more susceptible to other pathogens and insect pests.  Armillaria root rot is most problematic when combined with other stressors and thus changing climate, land use changes, and increasing invasion by pathogens and insects, increases its potential to harm forest trees.


Defoliating Caterpillars

There are many different species of caterpillars that can defoliate our trees.  While these can be pests, in most years they have negligible effects on trees and are a natural part of forest ecosystems.  Several, including Eastern Tent Caterpillars and Forest Tent Caterpillars can cause heavy defoliation in some years but are different from invasive threats like the European Gypsy Moth because trees typically recover.  However, combined with other pathogens and insect pests they may weaken a tree making it susceptible to other problems. 


Two-lined Chestnut Borer

The two-lined chestnut borer (Agrilus bilineatus) is an endemic beetle native to North America that attacks stressed or weakened oak trees. Larvae of the beetle construct galleries in the inner bark of trees, cutting off the flow of water and other nutrients.  This causes drought-like symptoms and tree death from the top down.  Two-lined chestnut borer is found throughout the eastern US and west to the Rocky Mountains.  Alone, two- lined chestnut borer may act as a natural thinning agent for aging or weakened stands.  However, combined with other stresses, (ex. European Gypsy Moth defoliation), two-lined chestnut borer may become a more significant cause of mortality.


More resources:

Visual guide to distinguishing European Gypsy Moth from other defoliating caterpillars.