Tree Pests & Diseases

Just as all plants are, trees are susceptible to various pests and diseases that can threaten their health. Most trees are vulnerable to diseases that are caused by bacteria, fungi, viruses and nematodes. It's important to recognize a problem in its early stage before it destroys a tree. By identifying a particular disease or pest and determining its degree of destruction, tree caretakers can decide what type of treatment is needed.


Aphids, which are common tree pests, are small insects with soft bodies. They range in colors including yellow, green, red, brown and black depending on their particular species. Aphids have whip-like antennae and cornicles, which are tube-like structures that project backward from their hind ends. These pests secrete honeydew, which is a sticky fluid that drips on plants and attracts ants which cause black mold to grow on leaves. Pinching or pruning off infested leaves helps control these pests, as well as does using insecticides. When there's a high population, it's best to use a toxic that's the least poisonous. Using botanical insecticides or insecticidal soap is also effective.

Gypsy Moth

The gypsy moth is one of the most destructive pests of urban landscapes and hardwood forests as each year it defoliates about a million or more acres, according to Planet These pests are mostly found in the eastern and northeastern regions of the United States. It's only during the caterpillar stage of the insect that these moths feed upon trees. Mature gypsy moths are about 2 inches long and are exceptionally hairy. Gypsy moths can be controlled by keeping the yard clean and removing dead branches, stumps and discarded items where an adult female is mostly likely to lay eggs. Insecticides can be applied to leaves when caterpillars are less than 1 inch in length while they're still young. The caterpillars are harder to control as they grow larger.

Fire Blight

Fire blight is a disease of fruit trees with quince and pear trees being the most susceptible. Infections of fire blight, caused by the bacterium Erwinia amylovora, are able to destroy limbs and entire trees. An initial signs of fire blight is a light tan water bacteria that oozes out of twigs, branches or trunk canker which are areas where bark has been killed by the disease in a prior season. Usually flowers are first infected with stems wilting and turning black or brown. The infection then moves on to twigs and branches. When fire blight causes a severe infection a fungicide such as Bordeaux can be applied.

Oak Wilt

Oak wilt, an aggressive disease infecting many types of oak trees, kills thousands of trees annually in woodlots, forests and home landscapes. The disease is especially found in the eastern regions of the United States. It's caused by the fungus, Ceratocystis fagacearum, which grows in water vessels of host trees. Leaves wilt and then drop off with a tree eventually dying. Although this fungus attacks all types of oaks, it's known to kill red oaks quickly within only a few weeks after an infection. Common symptoms are leaf discoloration and wilting. Fungicides are effective in preventing oak wilt, but these fungicides can't stop the disease in a tree that's already infected.

Keywords: tree diseases, tree pests, tree infections

About this Author

Venice Kichura has written on a variety of topics for various websites, such as Suite 101 and Associated Content since 2005. She's written articles published in print publications and stories for books such as "God Allows U-Turns." She's a graduate of the University of Texas and has worked in both Florida and Connecticut schools.