 |
Ornamentals and Turf |
As are most everything else, orangestriped oakworms are appearing early this year. The first indication of their presence is often fecal pellets on the driveway or sidewalk under an oak tree. Orangestriped oakworms are sometimes very abundant on oaks in late August and September. They occasionally feed on other hardwoods as well. The moths emerge in June and July and deposit their eggs in clusters of several hundred eggs on the underside of oak leaves. The eggs hatch in about a week or so. The tiny, green-colored caterpillars eventually grow into black caterpillars with yellow or orange stripes running lengthwise along their bodies. These caterpillars have a prominent pair of spines or slender horns sticking up behind the head. Young caterpillars feed in groups, whereas older caterpillars tend to be solitary although there may be thousands of caterpillars on a single tree. Small trees are sometimes defoliated completely by mid summer. Even mature oaks may be defoliated to the point that there may be twig dieback due to sun scald or other factors. As the caterpillars mature, they are often seen crawling along sidewalks and driveways, yards, etc. These caterpillars may wander for a considerable distance while searching for a place to pupate. They dig into the soil three or four inches and pupate there. There is usually one generation per year, and the caterpillars overwinter as pupae in the soil. Control is complicated by the size of many of the infested trees. Fortunately, late summer defoliations are much less damaging to the health of trees than early spring defoliations. In most cases it is probably better to rely on birds, diseases and parasites to lower the population the next year.
In late June or July the landscaper could put out some white trays or white pieces of cardboard to sample for the frass dropping out of the trees. The landscaper can detect the caterpillars before they are large enough to notice in the trees and can apply insecticide before the caterpillars do much damage. Also, younger caterpillars will be more susceptible to Sevin, Orthene and other insecticides. Chemical control on mature trees is rarely justified. For green control, early is the time to use B.t. or knock the caterpillars off of the trees. Conserve (spinosad) may also be used by landscapers and in nursery. If this is a perennial problem, install wasp nest boxes in the spring. Stepping on the crawling caterpillars may help reduce the population slightly and although these are not stinging caterpillars, it is still wise to wear shoes as one unlucky homeowner discovered last year.
Young azalea caterpillars are small, green-colored caterpillars that grow into medium-sized, purple-colored caterpillars and then into large-sized, black and yellow-striped caterpillars with red-colored heads and prolegs. Azalea caterpillars are gregarious in the larval stage, which makes their control relatively easy. However, because the caterpillars feed in groups, they often completely defoliate a portion of a plant before they are detected. There is only one generation per year. The adult moths emerge in early summer and deposit their eggs in masses of 80 to 100 on a leaf. As the caterpillars mature, they do more damage. Most of the damage occurs in August and September. Azalea caterpillars can be shaken from the shrub and trampled underfoot. Sevin, Orthene, and pyrethrin-based insecticides should provide adequate control as well.
Last week we received a call from one of the western counties about an outbreak of larger elm leaf beetles. Elms are the major host for larger elm leaf beetles, but they sometimes feed on dogwoods, hazelnuts, pecans, river birches, plums, and hawthorns. The larger elm leaf beetle often suddenly appears in great numbers, does tremendous defoliation for a year or two and then disappears for an indefinite time (perhaps decades). It is more damaging for an elm to be defoliated in the spring than later in the summer or fall, so the present damage is probably of little consequence to the health of these trees. Sometimes groups of larvae can be seen on the soil surface beneath a tree. The beetles overwinter as grubs in the soil. In spring they pupate, and the new adults emerge in May. Adult larger elm leaf beetles chew holes in the leaves and lay their eggs on the leaves. The larvae hatch and skeletonize the leaves as they feed. There is one generation per year. Adults may survive throughout the summer. This insect can be controlled with various pesticides. Ornamentals and Turf Information Note No. 24 has some additional suggestions for control of leaf-feeding beetles.
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 August 5, 2002 by Stephen J. Toth, Jr.
