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Urban Forestry
Tree Care: Pests and Insects

Insects and mites damage trees in two ways:

  1. they directly impact tree health by feeding of various parts of the plant, or
  2. they are transmitters (vectors) of tree diseases from tree to tree.

Most insects are species specific. If a plant is highly susceptible to a certain pest, you should avoid using it in urban settings. The key to keeping insects and other pests from damaging your trees is proper tree management. Insects attack trees weakened by other agents, biotic/abiotic. The key to pest management in urban trees involves proper selection, culture and maintenance.

Insects affect the above-ground portion of the tree and can be broken up into three basic categories: chewing insects, sucking insects, boring insects.

  • Chewing insects – primarily focus on the leaves and young stems of trees.
    • Eastern Tent caterpillar and Tussuck moth larvae can defoliate mature trees in about two weeks.
    • If the tree is healthy, most defoliators are merely a nuisance and the tree will regrow its canopy with little effect.
    • Repeated defoliations of young or old trees can weaken the tree.
  • Sucking insects – include scales, mites and aphids.
    • These insects primarily attach new foliage and stems. Rather than eating plant parts directly, like defoliators, they pierce the epidermal layers of the plant and extract sugars.
    • These insects produce mostly cosmetic deformities on the tree such as sooty mold, slow growth, tip dieback and galls.
    • If insects reach high populations, serious damage can occur.
    • Sucking insects are drawn to healthy, rapidly-growing trees dominated by rapidly-growing, sugar-rich parts.
    • The best preventative control is culture.
    • The use of low-nitrogen, slow-release fertilizers will eliminate sucking insect problems.
  • Boring insects – are of primary concern in southwest Florida.
    • Adult boring insects can sense stress and attack.
    • If boring insects choose a healthy tree, the tree will rebuff entry or tolerate and contain damage caused by the attack.
    • Boring insects use trees to house their eggs.
    • During the larval stage, the boring insects feed on the living tissues just beneath the bark layer.
      • This feeding disrupts the water and sugar flow in the tree, damaging living tissues in the trunk

Pest Signs and Symptoms
Pest control requires diligence on the part of the homeowner. All trees should be inspected every month for the following signs of pests or insects:

  • chewed foliage, twigs or blossoms;
  • streaked or mined foliage;
  • curling or twisting of leaves;
  • dieback of twigs and shoots;
  • sawdust or sap leakage from stems;
  • sticky honeydew on ground, stems and/or leaves;
  • tents, webs or sick masses in crown;
  • pitch tubes or gum masses on stems and branches.

Homeowner or managers should establish a tolerance level for pests, based on two thresholds:

  • defer pest control if you are willing to tolerate cosmetic or aesthetic injury to the plant or
  • set a tolerance or disturbance level beyond which you will resort to a pest management response.
 
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