Forest Pests and Diseases

Forest pests and diseases injurious to trees in Ontario are mainly transitory and occur infrequently in localized outbreaks of short duration.  They are mostly treated during a single phase of their lifecycle, making the timing of their control important.

Forest pests and diseases are generally grouped in the manner in which they harm trees.  Pests are grouped as:  defoliators, borers, sucking insects and mites, gall makers and root feeders; and diseases are grouped according to the part of the plant they attack:  below the ground; above the ground (woody tissues) and foliage.  Symptoms of infestation include:

  • wilted leaves
  • leaf spots
  • blotches and curls
  • discolouration of foliage
  • premature leaf fall
  • wounds and cankers
  • swellings and galls
  • bleeding and gum formation
  • deformed, dying, and dead parts  (Ministry of Natural Resources).

If you believe that you have a problem with pests and diseases in your woodlot, visit the resources available on our website, or contact Forestry Services staff to discuss control strategies.

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