Forest Publication - Common Pests of Trees in Ontario

Tree pests are capable of causing considerable economic damage. No species of tree, no part of a tree, and no stage in the development of a tree is immune to pest attack. From the time trees are set in the soil they are subject to the attacks, or the effects, of numerous agents which may kill them, retard their growth, deform their shape or symmetry, weaken or degrade the wood, or otherwise adversely affect their functioning or mar their attractiveness.

The importance of the injury is relative to the purpose for which the trees are being grown, managed, or utilized. The intensity of control efforts undertaken is similarly determined by the value of the trees at risk and the type or degree of damage.

Prevention of attack is the first line of defense against tree pests. Good cultural practices should be emphasized as a means of maintaining tree vigour. Vigorously growing trees are generally better able to resist attack by insects and diseases or to withstand periods of adverse weather or other stress conditions. If attacked, they are better able to recover from the effects of the infestation or infection.

However, when an outbreak or epidemic occurs or appears imminent, direct control through the use of pesticides is sometimes required to mitigate damage. The use of trade, firm or corporation names in this publication is for the information and convenience of the reader. Such use does not constitute an official endorsement or approval by the Ministry of Natural Resources of any product or service to the exclusion of others that may be suitable.

Pesticide products mentioned in this publication have been reviewed by the Ontario Pesticides Advisory Committee and have been classified under the Ontario Pesticides Act.

Chemical Safety

The usefulness of pesticides rests on their ability to interrupt the life process of insects and fungi. By their very nature, pesticides are poisons and must be handled properly to prevent unwanted and dangerous effects to humans, non-target organisms, and the environment. Pesticides may be taken into the body by breathing, swallowing, or absorption through the skin. However, even the most toxic compounds can be used safely if the recommended precautionary measures are observed.

• Purchase only the quantity of pesticide needed for a particular problem or for a single season.
• Inspect pesticide containers for leaks before handling them. Do not handle containers roughly or carelessly.
• Read the entire product label to ensure that the plants to be treated are not sensitive to the chemical. Follow the directions and safety precautions carefully. If seeking medical aid, take the label and/or container with you.
• Do not rub the eyes, touch the mouth, or smoke while working with pesticides. Wash hands thoroughly before eating, drinking, smoking, or using the toilet.
• Wear clean rubber gloves and protective clothing when handling pesticides, and use a respirator whenever recommended. Thoroughly wash contaminated clothing separately and discard faulty protective clothing.
• Clean up any pesticide spill immediately. Use dry soil, sawdust, or other absorbent material to remove excess liquid.
• Do not leave pesticide containers unguarded while spraying and ensure that children and pets are kept well away.
• Do not work alone with a hazardous chemical.

Toxicity and Lethal Dose

Pesticides vary widely in their toxicity. Toxic effects may be acute or chronic.

The susceptibility of animals to poisoning by a pesticide varies with the type of formulation used, the route of entry into the body (oral, dermal, or respiratory), and the weight, age, sex, and nutritional state of the individual affected.

The accepted method of recording the relative toxicity of a pesticide is the Lethal Dose 50% (LD₅₀) value. This is a statistical estimate of a chemical dose which, when administered, will kill 50 per cent of the test animals under stated conditions.

The figures which designate the LD₅₀ values are expressed in milligrams of dose per kilogram of body weight of the test animal. Therefore, the higher the LD₅₀ value, the less acutely toxic the material.

Storage of Pesticides

• Pesticides should be stored in their original containers in a cool, dry, locked, well-ventilated area without floor drains.
• Pesticides should be stored away from food and drink used for human and animal consumption.
• Herbicides should be stored separately from other types of pesticides to prevent cross-contamination.
• A chemical-storage warning sign should be placed on the outside of each entrance leading into the storage area.
• Protective clothing and a first-aid kit should be available in the storage area.

Disposal of Pesticides

• Immediately after emptying a pesticide container, rinse it at least three times with the same dilutent used for mixing the spray. Pour the rinse into the spray tank and puncture the bottom of the container. Do not reuse pesticide containers or convert them to other uses.
• All empty containers and unused amounts of pesticides must be securely held in an isolated storage area until they can be
  disposed of correctly. Triple-rinsed or jet-rinsed containers of most commonly used pesticides can be disposed of with
  household garbage.
• Where regular garbage disposal is not practical, dispose of empty pesticide containers in a landfill site or bury under at least 50 cm of soil, away from water.

Benefit/Risk Relationship of Pest Control

The aim of pest control is not the eradication of a pest species, but rather the maintenance of a balance between the pests and their host trees at a level below the threshold of serious injury. The decision to invoke control measures depends upon the benefits to be received in relation to the costs incurred. The value of the material saved must justify the expense involved, or the cost of control must be less than the loss that would result if no intervention were made. If the use of pesticides is the most efficient method of control, then:

• Select the least toxic material and use the lowest concentration that will do the job effectively.
• Apply the smallest amount necessary and in a manner that will have minimum effect on non-target organisms and nontarget areas.
• Make application at the weakest point in the pest’s life cycle.

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