Pests That Attack Tree Leaves

• A number of insects attack leaves -- including aphids, whiteflies, scale insects, caterpillars, moths, bagworms, leafminers and spider mites. There are also pests that attack specific species of trees and the leaves, including the pear psylla, which affects pear leaves. Insect pests hatch and feed on leaves at different times during the growing season, which affects the type of damage that's done and when the damage occurs. Varying pest types and maturation rates affect the way pesticides are used on leaves.
  
  

Damage Caused by Insects

• Aphids and scale insects are sucking insects. They bite holes in the leaves and suck out sap, leading to yellow, withered leaves. Black cherry aphids look like small black beetles and attack tart cherry trees. European elm scales attack elms and create small white protective layers around their bodies. Other insects, like caterpillars, feed on the flesh of the leaves, which leads to holes and leaves with brown or yellow edges. Severe pest infestations may defoliate a tree, preventing it from growing.
  
  

Pests and Disease

• The damage insects cause to leaves of the trees makes the tree more likely to contract bacterial and fungal infections. Some insects, like aphids, sometimes carry diseases with them, which they transmit to the tree while feeding. Additionally, the secretions left behind by aphids and scale insects create a place for the fungal disease sooty mold to grow.The holes left in the leaves by insects like caterpillars allow diseases and fungal spores to enter and infect the tree.
  
  

Pesticides

• Pesticide sprays protect the leaves of trees from insect damage by making it toxic for the insects to eat them. Pesticides applied on a regular schedule throughout the growing season stop pests in all stages of growth from feeding on the leaves, and kills eggs laid in the tree. Apply pesticides according to the directions on the package to avoid using excess chemicals. Prune the tree annually to remove dead and damaged limbs, as these provide a place for insect pests to start attacking the tree.