Summer is a great time to inspect the health of your trees. Start by looking at the leaves. Is there discoloration, shriveling, spots or evidence of insects? Inspect the branches and tree trunk for anything that looks abnormal. Are there areas where the tree was damaged by a mower or string trimmer? Look for possible evidence of sun scalding, holes in the trunk or signs of pests or disease. Lastly, look at the root system and check to see if the first roots are coming away from the tree and into the ground.
Cankers are a discoloration of the bark, which results from a fungus getting into the tree. The picture below is of a tree infected with Cytospora which is most commonly found in fruit trees, poplars and woody shrubs. The best way to prevent cankers is to prevent stress on the tree. Drought and oxygen starvation of the roots by flooding soils are the two most common stresses that predispose infection. To treat a canker, it is best to prune during dry weather, and make cuts with a sterilized cutting tool at least 4 inches below the edge of the canker, and make sure to resterilize the cutting tool as to not infect other trees.
Also, look for any decay, cracks, splits, and weakly attached branches. Sun scald is another aliment that can cause damage in trees. This is caused by intense sunlight on the trunk of young trees that don’t have mature bark yet. The lower angle of the sun and intense light can “burn” the young bark. To help aid younger trees, a tree wrap is applied in November and taken off in April.
There are also three main types of pests that can effect tree health: defoliators, wood borers and sap-sucking insects. If trees are healthy then pests may have minimal effects on the trees’ health. However, if a tree is already stressed, these pests can certainly kill a tree.
Defoliators eat the leaves of trees and can do a lot of damage. For example, western tent caterpillars are one type of insect that attacks a wide range of trees and shrubs. Wood borers bore into the wood of the tree and the larvae of the beetle does most of the damage. In Colorado, the Emerald Ash Bore will eventually kill all of the ash trees, which why now is more important than ever to plant a variety of trees to diversify the urban canopy. Below is a picture of emerald ash bore. If you find any, please report to USDA. Sap-Sucking insects eat away at the sap in trees leaves and stems, and the most common are aphids and scale insects.