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Scouting Watch

April 21, 2004

Hemlock rust mites cause hemlock foliage, particularly the older needles, to turn yellow and fall off the tree. Heavy infestations can cause severe defoliation. These are eriophyid mites, which are too small to be seen with the unaided eye: With a 10X hand lens, they appear as elongated, cigar-shaped mites with all four legs at the front of the body. Treatment at this time with bifenthrin (Talstar), insecticidal soap, or summer spray oil reduces damage through the season.

Juniper webworm and arborvitae leafminer overwinter as larvae and become active in the spring. At this time, they are active and can be controlled with thorough applications of acephate (Orthene). Juniper webworm causes the foliage on branches or entire plants to turn brown, usually in early summer. Fine silk webbing will be on the branches. Arborvitae leafminer mines in the scalelike leaves in late summer but becomes more exposed to insecticides when feeding resumes in the spring. Tips of branches turn whitish and then brown. With severe infestations, entire arborvitae shrubs or trees turn brown.

Northern pine weevil is primarily a pest to Christmas tree growers. This insect develops as larvae in old stumps, emerging at this time as adults that move to seedlings and other pines nearby. They feed on the bark of small branches, causing dieback. Seedlings are likely to die, and larger trees can lose branches, resulting in unsalable trees. Spraying the stumps at this time with cyfluthrin (Tempo) or permethrin (Pounce, Astro) kills the emerging beetles. Removing stumps or leaving one live branch to keep the stump alive, prevents this insect. Growers that harvest fields at one time do not have this insect problem, as stumps are not near growing trees and seedlings.

Multicolored Asian lady beetles are very numerous at this time inside buildings. These 1/4-inch-in-diameter, orange to red beetles, with typically 19 black spots, have spent the winter inside the walls. Now that the walls are warming due to higher outside temperatures, the beetles are becoming active. As it is still too cold to stay outdoors, they come to the inside, where it is warmer. They do not reproduce indoors and will move outside for summer when it gets a little warmer. Vacuuming the beetles and dumping them outdoors is the most effective control at this time. Small light traps for use indoors are available that attract and catch these beetles at night.

Author: Phil Nixon Morton Arboretum


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