By Dennis Tompkins
Various pests are beginning their annual feasts as new growth emerges on our landscape trees and shrubs.
If a homeowner wishes to attempt to control a pest, there are three rules that must be followed: 1) Have the pest properly identified; 2) Determine the appropriate treatment by asking nurseries and reading pesticide labels; and 3) Apply the recommended treatment at the proper time and at the recommended rate.
If these rules are not followed, the treatment will be wasted.
Help in identifying problems can be obtained by taking samples to Master Gardener clinics. Inviting a professional to visit your landscape will eliminate guesswork and will be the best chance for a proper diagnosis.
The following are signs of some of the more common insects and diseases that will be visible. Please note – most of these pests do not kill their hosts.
Insect Damage
Colorado blue spruce: old dead brown tops. Pest: white pine weevil larvae have been feeding on the top leader in the past. Other branches may have turned up to form new tops. New growth that is under attack will soon begin to wilt. Treatment: if reachable, cut out the drooping top below where the larvae are feeding and destroy them. Sprays are not practical.
Various spruce species: severe loss of interior needles and sections where branches have died. Pest: most likely the spruce aphid – a tiny green insect that does its damage in late winter. Treatment: tap the foliage to dislodge insects onto an index card. If very tiny green spots begin to slowly move, you’ve got them! Hose small spruce trees with high-pressure water or spray larger trees with insecticides. Note: any fast-moving insects are likely beneficial predators.
Flowering plums and cherries: curled or wrinkled leaves. Pest: most likely aphids visible as tiny, light-colored insects when the infected leaves are uncurled. Treatment: they can be sprayed but generally are not worth worrying about.
Alpine or subalpine fir trees: ugly, deformed branches often curled like a bird’s claw. Pest: balsam woolly adelgid – a devastating insect pest of Fraser, alpine and sub-alpine fir trees. Visible when new growth begins as tiny white cottony tufts on the undersides of branches or on the trunk. Treatment: difficult to control, but can be sprayed for as the new growth expands and the tiny crawlers begin to hatch. Badly deformed trees should be removed.
Disease Problems
Flowering cherries: infected blossoms will die and persist on the branches; small cankers may produce gumming and kill small branches that will be visible this summer. Pest: most likely brown rot, a common fungus on cherries. Treatment: can be ignored or fungicides can be applied beginning when blossoms begin to open, at full bloom and during petal fall. Very difficult to control.
Flowering plums and cherries: leaves with several small holes, sometimes premature heavy loss of leaves. Pest: Coryneum blight or “shothole” fungus. Treatments: rake and destroy leaves. Fungicides can be applied at leaf fall in late summer and in the spring when flower petals have fallen and the leaves begin to emerge.
Dogwoods: new leaves wrinkle up and have brown splotches; can have premature heavy loss of leaves. Pest: most likely dogwood anthractnose – a very common fungus that infects many native and non-native dogwoods. Treatment: rake and destroy fallen leaves. Fungicides can be applied at bud break and continued at 10- to 14-day intervals until weather dries out. Resistant varieties are available at nurseries.
Japanese and lace-leaf maples: suddenly wilted foliage that hangs on the branches; may start with a single branch dying and spreading to others. Pest: possibly verticillium wilt – a soil-borne fungus that affects roots and spreads upward throughout a tree. Infected trees may be killed outright or may tolerate the fungus for several years. Treatment: prune out and destroy infected branches. No controls are recommended. This is a highly contagious disease of maples and several other hosts. Dig out as many of the roots as possible if removing a diseased tree that has become unsightly.
Personally, I am not anti-pesticide. But I choose to live with most of the pests unless they threaten the health of a plant or cause it to become an eyesore.
Dennis Tompkins is an ISA Certified Arborist, ISA Qualified Tree Risk Assessor and Master Gardener from the Bonney Lake-Sumner area. He provides pest diagnosis, hazardous tree evaluations, tree appraisals, small tree pruning, and other services for homeowners and businesses. Contact him at 253 863-7469 or email at dlt@blarg.net. Website: evergreen-arborist.com.
