Aphids cause deposits of honeydew on lower leaves. Spraying large trees may not be necessary as predatory insects will bring the aphid population down. Use malathion, Orthene, or Diazinon.
Imported willow leaf beetles are metallic blue and the larvae are black. The larvae do most of the feeding on leaves. The adults eat the entire leaf while larvae skeletonize the leaves. There are two generations per year. Use Sevin or methoxychlor when beetles or larvae are first seen.
Lace bugs cause mottling and yellowing of the leaves. The insects are small, found under the leaves, and have transparent wings with dark veins. Use Orthene or malathion when lace bugs are first seen. Repeat in 10 days and again in several weeks if the infestation re-occurs.
Poplar and willow borer bore in the trunk and may be serious on newly planted trees. In spring the insects expel frass through openings in the trunk. The frass clings to the bark. Spraying may be done in late fall or early spring and should be applied to large limbs and the trunk.
Scales can be controlled with sprays of Orthene, Diazinon, Sevin, or malathion applied to control the crawlers. Apply Orthene 2 to 3 times at 7 to 10 day intervals when crawlers are first noticed. Diazinon, Sevin and malathion may be used when crawlers are present.