By Dennis Tompkins
The Evergreen Arborist
Spring is finally arriving. As the new leaves begin to expand, various critters will be licking their chops waiting for the feast to begin. The following are symptoms of some of the more common and highly visible insect and disease pests that will soon be eyeing your landscapes.
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 will soon be visible and under attack, so it will soon begin to wilt.
Treatment: if possible, cut out the drooping top below where the larvae are feeding and destroy them. Sprays are not practical.
Dwarf Alberta spruce and blue spruce: 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: in February and 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. They are visible as tiny, light colored insects; 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 presently 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 develops within a few weeks when the tiny crawlers begin to hatch. It is not practical to spray large trees. Badly deformed ones should be removed.
Flowering cherries: dead small branches, dead blossoms still hanging on branches, small cankers that produce gumming. 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 can infect 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 or can 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
Many of the pests noted above do not kill the host tree. They can be ignored if one chooses not 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.