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Ornamentals and Turf |
The maple eyespot gall midge, Acericecis ocellaris, is also called the maple leafspot gall midge. The word ocellaris is derived from the Latin word ocellus meaning eye (hence the name eyespot gall). Maple eyespot gall midges emerge in early spring and lay their eggs on the newly-expanding leaves. As the maggots hatch and feed on the underside of tender leaves, they secrete substances which cause the leaves to form dimples around the maggots resulting in striking yellow and red circles on the top of the leaf around the gall. The maggots soon mature and drop to the soil surface where they evidently dig into the soil to spend the rest of the summer, fall and winter. Another generation of midges will emerge the next year. Insect populations vary from year to year due to weather, predation, diseases and additional factors; thus, the maple eyespot galls may be much less noticeable next year. Because they do negligible damage, management is not necessary.
Almost every other arthropod pest has been early this Spring, so why not spider mites? Keep your eye out for these pests before they create damage. Spider mites are tiny warm season arthropods that insert their tiny, scissor-like mouthparts into leaves and petals and cause tiny yellow spots to form as they suck out the contents of the plant cells. Hot, dry weather apparently inhibits parasitic fungi and accelerates the life cycle of the spider mites. Daylilies, roses, butterfly bushes, some euonymus and bedding plants are often infested by spider mites during the summer. Because spider mites flair up in dry weather, their control is somewhat difficult. Plants that have wilted slightly are much more susceptible to pesticide injury than turgid plants. Also, plants are much more likely to be burned if pesticides are applied during midday. Plants should be watered thoroughly before spraying them with pesticide and should be sprayed in early morning or late afternoon so that the pesticide residue is dry before the bright, noon sun hits it. Horticultural oils and soaps are moderately toxic to spider mites and they are relatively safe for humans. Soaps and oils have virtually no residual activity so both pesticides must be applied two or three times for complete control (about 5 days between sprays). It may be a long season! Horticultural oils have been shown to be less harmful to beneficial predatory mites. For commercial nurserymen, Joust also gives excellent control of spider mites and mite eggs on trees, shrubs and flowers (however it is not labeled for use in the greenhouse). Avid is now labeled for spider mites outdoors except on coniferous evergreens. Floramite is another excellent miticide for mobile stages and is labelled for greenhouse, nursery, and landscape use. It is also compatible with many beneficials.
The predatory mite Phytoseiulus persimilis can give good twospotted spider mite control in the greenhouse and may work in against this mite in Southeastern landscapes and nurseries because it prefers higher temperatures and relative humidities compared to other predatory mites.
Spiny witch-hazel gall aphids, Hamamelistes spinosus, cause bumpy ridges on the leaves of birch. The overwintering eggs are laid on witch-hazel in June and July. These eggs hatch the following spring and the new aphid nymphs crawl to the witch-hazel flower buds to feed. A second generation of winged aphids develop inside the galls, then leave and fly to birch. These winged aphids give birth to a scale-like generation of insects which settles and hibernates on birch until the following spring. As the buds break, the scale-like aphids feed on the leaves and induce the birch to form corrugated galls. This aphid requires two full years to complete its cycle of life stages. Pesticides should be applied at bud break in early spring to prevent gall formation. It may almost be too late this year for effective control. The alternation of hosts is well known for other aphids (woolly apple aphid on apple and elm, woolly alder aphid on maple and alder, and green peach aphid on peach and many other hosts), but the spiny witch-hazel gall aphid seems to have the most complicated life cycle. This is mostly a cosmetic problem and few trees are severely harmed. Ornamentals and Turf Insect Note No. 38 provides information on general aphid management.
We have not received any reports yet for rhododendron borers, but pest problems have been early this year. Adult rhododendron borers, active in May and June, are small, black, clearwing moths with white and yellow markings. These moths lay their eggs on the bark of rhododendrons, azaleas, and mountain laurels. Tiny caterpillars hatch from the eggs, bore into the sapwood, and develop into inch-long worms. The boring by the caterpillars may cause the stem to wilt. If the stem is large enough it may not wilt. Sometimes the first indication of rhododendron borer infestation is that the stem breaks off. Pruning and burning heavily-infested parts of the plants is component of the management for this pest.
Last week we received a report of a severe infestation of honey locust plant bugs (Diaphnocoris chlorionis) from Lenoir County. This small, green true plant bug has one generation per year and overwinters as an egg in the woody stem tissue. Upon hatching in the spring, the first instars feed on the unfolded leaflets and may cause distortion and discoloration. Defoliation may occur. Sevin and pyrethroids may be helpful to reduce populations, but mite outbreaks are more likely after treatment. This is likely to be a yearly event to varying degrees. Horticultural oil applied at the summer rate may is another choice. For one or two specimen trees, imidacloprid soil drench or soil injection may be effective if applied three to four weeks before egg hatch.
Boxelder bugs feed on the seeds of boxelder trees and to a lesser extent on the seeds of maples and ash trees. Sometimes these bugs can become quite abundant on maples or ash trees. However, when boxelder bugs annoy people year after year it is usually because they have a female boxelder tree in the yard or in a yard or lot nearby. Ornamentals and Turf Insect Information Note No. 40 provides additional information on boxelder bugs. Boxelder bugs are a more frequent complaint later in the season but it is not uncommon to receive complaints at this time of year. If desired, any pesticide should be directed onto the bugs to kill them, not onto the tree or noninfested parts of the house.
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 May 6, 2002 by Stephen J. Toth, Jr.
