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Ornamentals and Turf |
Last week I received a plant sample from Cherokee County with what appeared to be damage from the yellow poplar weevil. Both adults and grubs of the yellow poplar weevil damage yellow poplars, magnolias and sassafras (also called the tuliptree leafminer, magnolia leafminer and the sassafras weevil). These tiny weevils (about 1/8 inch in length) feed on the buds and leaves. Their grubs mine in the leaves. The adults overwinter in leaf litter under the host trees. On warm spring days they fly up and feed on buds and leaves. In May, eggs are laid on the midrib and the resulting grubs mine the leaves and cause blotch-type mines. Usually the blotch starts near the tip of the leaf. The yellow poplar weevil is a sporadic pest, and outbreaks occur at irregular intervals. By early July, yellow poplar weevils are relatively difficult to find. Apparently they have already descended to the leaf litter to spend the rest of the summer, fall and winter. Because yellow poplars can be very tall, these insects may be out of reach of the sprayers most homeowners use. This insect does not cause permanent damage and treatment with insecticide is probably not needed. Even heavily-damaged trees can compensate for the early season leafmining by the end of the summer. If timed early, only small specimen trees or nursery stock might benefit from treatment.
The lesser canna leafroller is a small caterpillar related to the European corn borer. It overwinters as larvae in the leaves and stems of canna and the moths emerge to mate and lay eggs after the new growth emerges in spring. When the larvae hatch, they feed within the new, still-rolled leaves. Older larvae can actually tie the edges of older leaves together and roll the leaf back up! If not managed, lesser canna leafrollers may completely destroy the aesthetic value of cannas. Larvae are actively feeding at this time. One mistake canna growers make is to leave the old dead growth on the canna bed as a sort of mulch. Canna seems to be the only host plant for this pest, so that if the plants are somewhat remote from other cannas it may be possible to drastically reduce the lesser canna leafrollers just by carefully removing all dead leaves and stems in the fall after the frost has killed it. It is possible to eradicate this pest by applying insecticide (Conserve, Orthene or cyfluthrin) several times perhaps at ten-day intervals. Bacillus thuringiensis insecticides are also effective for this pest. Spray the dilute pesticide mixture directly downward into the rolled leaves so that the pesticide can penetrate into the shelter around the larvae. Also pick up and destroy all of the dead tops from the cannas this winter after frost.
Spider mites are still out there and are not going away any time soon. Don't say we didn't warn you. See the May 3, 2002 issue of the North Carolina Pest News for more information on spider mites.
An unsuspecting Chatham County woman was checking her garden this week when she suddenly noticed some uninvited caterpillars feeding on her hibiscus. The caterpillars of Atomacera decepta feed on hibiscus, rose of Sharon, hollyhock, mallow and perhaps other members of the cotton family. This insect could be called the hibiscus sawfly as hibiscus is the most frequently-reported host plant. The adults are small (3/16 inch in length), black-colored, fly-like insects in the family Argidae and are a type of wasp rather than butterfly. The thorax is reddish-brown in color on the top. The argid sawflies are interesting because their antennae split almost at the base so they appear to have four antennae instead of two! There has been no detailed study of the life history of the hibiscus sawfly, but the caterpillars have been found from May to October. It is speculated there are up to six generations per year. The pale green larvae have black-colored heads and tiny black-colored spines on each body segment. They are slightly gregarious with up to three larvae feeding on one leaf. When mature, the larvae spin a tough silken cocoon on the base of the plant or nearby. From the cocoons emerge new adult insects to mate and lay eggs. The eggs are inserted into the leaf tissue one at a time. This insect should not be particularly resistant to pesticides; therefore, Sevin insecticide should give adequate control. Be sure not to spray open blossoms to avoid killing pollinators. Knocking the caterpillars off of the plants and squashing them is just as effective and requires no chemicals.
Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age or disability. North Carolina State University, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.
Last modified on June 3, 2002 by Stephen J. Toth, Jr.
