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Some Diseases and Insects Affecting Spruce Trees

Urban Forestry Home

Please note, residents are asked not to interfere with trees on Town property. To request an inspection, please contact the Urban Forestry Section at (905) 771-8800, Monday to Friday between 8:30 a.m. and 4:30 p.m. or fill out the Public Property Tree Reporting Form. Upon inspection, information will be left for the homeowner detailing the course of action by Town staff.

Diseases Affecting Spruce Trees

Cytospora Canker
Image shows a Spruce tree with white, crusty build up on its branches due to Cytospora Canker infection.Cytospora Canker is caused by a wood rotting fungus and usually infects trees under stress due to poor growing conditions. It forms in layers beneath the bark causing dead sections within the trunk.

Signs and Symptoms
  • A characteristic symptom is sap oozing from infected branches or trunks (white crusty build-up is present).
  • Needles of the infected branch will turn yellow to brown as the branch is encircled from within and isolated.
  • As the branch is constricted, needles will eventually drop off.
  • The tree will become scruffy and eventually may die.
Control Methods
  • It is difficult to control using chemicals.
  • You can increase the health of the tree by mulching, watering and fertilizing.
  • Remove the infected branches.
  • Prune Spruce trees only during winter months or in dry weather.
Insects Affecting Spruce Trees

Yellow-Headed Spruce Sawfly
Image shows mature Larvae of the Yellow-Headed SawflyAdult yellow-headed spruce sawflies emerge in the spring just as the buds on spruce trees are beginning to swell. Females deposit eggs singly into the base of new needles. Worm-like larvae, which have brownish-orange heads and green bodies marked with six greyish-green stripes, emerge within two weeks and begin feeding on the newer growth at the tips of the branches.

Are they on my tree?
  • The Yellow-Headed Spruce Sawfly is mainly found in mid-June to early July.
  • It has been found throughout the Town. 
  • If a tree is infected it will appear to have needles missing from the tips of its branches.
Control Methods

  • For smaller trees:
    • Wearing rubbers gloves, hand-pick the individual caterpillars and dispose of them.
    • Contact a garden centre for other control measures.
  • For larger trees:
    • Consult a commercial tree care/service company for appropriate control measures.
    If left untreated, successive years of defoliation can cause severe damage or death as lost needles cannot be replaced on the same twigs.

    Spruce Gall Aphids
    Image shows damage from Gall Aphid infestation. Note the brown ends of the branches.Spruce Gall Aphids are one of the most commonly occurring aphids locally. In general, aphids are small insects with soft, pear-shaped, green, yellow, black or colourless bodies. Their long, slender legs allow for slow movement.

    Signs and Symptoms
    • abnormal growths at the ends of branches, ranging from red green to reddish purple in the spring;
    • growths turn brown during summer months; and
    • are 2-6 cm in length and approximately 1-2 cm in width.
    What Causes These Growths?
    • As small insects feed they inject toxic saliva into the bud.
    • The plants react by forming a gall around the insect.
    • Small insects tend to be protected from weather, chemical sprays and predators.
    Control Methods
    • Due to the galls protection, timing of control is critical.
    • For large populations, dormant oil applied prior to shoot elongation in the springtime will work.
    • Oil should not be used on Blue Spruce varieties, as blue colour will be washed from needles.
    • For smaller populations, hand-pick from the tree and dispose while galls are still moist and green.
    • Infestations will not usually kill a tree, however, the tree may be left severely deformed, unattractive and weakened to other insects or diseases.
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