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Pest Watch

June 9, 1999

Black vine weevil adults have emerged, and adult feeding damage is being found throughout the state. This insect is a major pest for nurseries because it damages the roots of yews and other susceptible plants. In a landscape with established plants, root damage is less important. The larger concern is that the adults eat notches out of the leaf margins of euonymous, rhododendron, yew, and other plants. To gain control, you must eliminate the adults now before eggs are laid. The adults feed for about two weeks before their ovaries mature and they lay eggs. Several insecticides are effective, but it is important to get heavy runoff during spraying. This controls adults under the plants during the day as well as when they are feeding on the foliage at night.

Bagworm should be hatching any day now. Remember to delay spraying for about two weeks after egg hatch to allow all the eggs to hatch and the larvae to blow from tree to tree. This allows one spray rather than two.

European pine shoot moth and Nantucket pine shoot moth are major pests of Christmas trees throughout Illinois. They are both susceptible to dimethoate (Cygon) and other insecticides. They tunnel in the candles, causing shoot death and multiple-trunked trees. Shearing in mid-July also helps control these pests.

Potato leafhoppers and their damage are evident on red maples in the Bloomington area. They are probably present throughout the state. Applying a pyrethroid insecticide at this time will protect the trees for several weeks.

Spruce spider mites are still numerous in the Bloomington area, although it is getting late for this pest. Typically, this mite begins to enter the egg stage at about this time of year. Eggs are not controlled by most miticides. Be sure to scout before you treat.

Oystershell scale crawlers are present in northern Illinois. The brown or apple race appears as crawlers before the gray or lilac race. Be sure that the crawlers are present before treating.

Sawfly larvae are being seen on European ash, alder, black locust, elderberry, and hazelnut at The Morton Arboretum in northeastern Illinois. Although these larvae are similar to caterpillars in appearance, they are really wasp larvae. As such, they are not controlled with B.t.k.; instead, they require carbaryl (Sevin) or another chemical insecticide to achieve control.

Thrips are also present in large numbers on woody ornamentals throughout the state. Thrips feeding may cause distortion of emerging leaves and light streaking that later turns brown or forms callous patches on older leaves. Thrips attack flowers heavily; they can cause distortion and streaking on petals and reduce flower emergence. The amount of damage in Illinois typically does not warrant control, but this year it might. Consider treating very heavy infestations with spinosad (Conserve).

Author: Phil Nixon staff at The Morton Arboretum


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