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Spring pests are waking—how to spot them and get rid of them
A new growing season is upon us. As new foliage begins to appear, various pests are lying in wait to begin their annual feasts. The following are signs of some of the more common and highly visible insects and diseases that are or soon will be visible.
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 multiple tops. New growth that will soon be visible and 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: beginning in March, tap the foliage to dislodge insects onto an index card. If very tiny, green spots begin to slowly move, you’ve got them! Hose the plants with high-pressure water or spray with insecticides. 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 and/or their shed skins may be left behind. Treatment: They can be sprayed for 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 very devastating insect pest of true fir trees. Visible when new growth begins as tiny, white, cottony tufts located 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. It is not practical to spray large trees. Badly deformed ones should be removed.
Flowering cherries: signs are now visible as dead blossoms still hanging on branches, small cankers that may produce gumming and many dead small branches. Pest: most likely brown rot, a very 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. 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 sprays 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.
Rules for Pesticide Treatments
Most of the pests noted above do not kill the host tree. They can be ignored if one chooses not to use pesticides. If a chemical treatment is desired, here are three rules that must be followed:
1) Have the pest properly identified. 2) Determine the appropriate pesticide by asking nurseries and reading labels. 3) Apply the recommended pesticide 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 or inviting a professional to visit your landscape.