Common Insect and Disease Problems

The effect that disease organisms and insect pests have on the health of a tree ranges from very mild to devastating. In the 1900’s the entire population of two of America’s most celebrated shade tree species, the American elm and the American chestnut tree were essentially destroyed by disease organisms. More recently two notable conifer species; the Fraser fir and Eastern hemlock are threatened by extinction due to insect attack. The one factor that the four trees share in common is that the organisms attacking them are exotic species. For the most part our native trees have coexisted in the forest with native diseases and insects. Major epidemics are rare and typically occur only when catastrophic events such as drought, flood and fire stress trees by weakening their defense system making them more susceptible to attack. In urban areas man can offset these events through irrigation, flood control and fire fighting programs, however, urban trees encounter a wide variety of different stress sources.

The urban environment is very stressful to trees. Urban trees have to cope with compacted soils, air pollution, high soil temperatures surrounding the roots, barriers to root growth such sidewalks, curbs, foundations and utilities, soil pH problems, water run off, poor nutrient cycling, reflected heat, mower and string trimmer damage, herbicides, vandalism, improper pruning, poor structure and root loss due to excavation activities. All of the aforementioned problems disrupt the photosynthesis process and reduce the tree’s overall production of food (energy). If the loss of energy is substantial the tree’s defense system can fail. As in forest trees most life threatening disease and insect problems occur when a tree is stressed. Exceptions are some exotic insects and diseases. The tree has not evolved with these organisms and consequently has not developed a defense system against them.

The best strategy to avoid serious health problems to your trees is to keep them healthy. This means making sure your trees are: watered during droughts, mulched to increase nutrient cycling, afforded adequate rooting areas, not subject to damaging herbicides, grown in soils that supply the tree’s nutrient and pH requirements, protected from physical wounds and pruned and maintained according to industry standards. The following is a look at some common disease and insect problems of conifers, hardwoods and palm species. If you think your tree has an insect or disease problem consult with the Cooperative Extension Service or an ISA Certified Arborist.