Photo Gallery of Insects and Mites on Ornamental Plants
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Fall webworms are beginning to appear on their favorite trees: sourwood, pecan, and persimmon. Fall webworm damage accrues over the summer. They usually cause little long-term damage to the health of the trees they defoliate unless the trees are completely defoliated year after year. At any one location, the populations of fall webworms wax and wane so that they are conspicuous and damaging for a year or two and then the populations seem to disappear.
Through the summer, the webs become filled with cast skins, droppings and dead leaves. The web is enlarged to encompass fresh, green leaves until the web may become two to three feet in length. Small trees infested with several broods of caterpillars may be entirely enclosed in webs. After feeding for four or five weeks, the caterpillars crawl down, spin cocoons and pupate in mulch or soil. In July and August, another generation of moths emerges from the cocoons to continue the life cycle. There are two or three generations each year in North Carolina depending upon how early or late in the spring the first moths emerge. They overwinter as pupae in cocoons in the litter.
White fall webworm moths emerge to mate and lay 350 to 900 eggs on the lower leaf surface. The hairy caterpillars spin the webs as they feed. Fall webworms can be destroyed by pulling down the webs and destroying the caterpillars if the webs are in reach of a pole. If the webs are within reach of a hose-end sprayer, several insecticides can be sprayed for control. Insecticides work best when the caterpillars are young. Thus it is best to treat as soon as the webs are first noticed. If the trees are too tall for equipment used by the amateur horticulturist, many professional landscapers and arborists offer tree spraying as a part of their services. Bacillus thuringiensis and Orthene are two of several pesticides labeled for fall webworm control. Ornamentals and Turf Insect Information Note No. 7 has additional information on the control of fall webworms. Copies of this note are available in the county Extension centers in North Carolina.
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), black-colored, fly-like insects in the family Argidae. The thorax is reddish-brown 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 worms 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 adults 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. Sevin should give adequate control. Be sure not to spray open blossoms to avoid killing pollinators.
Juniper tip dwarf mites are microscopic animals that feed by piercing the needles or buds of junipers and injecting their saliva. They then suck out the contents of the cells in the vicinity of the feeding wound. Some varieties are sensitive to eriophyid mite saliva and respond in several ways. A few junipers are apparently sensitive enough that the buds die after enough mites have fed in them. Other junipers develop odd-looking growth that looks almost like herbicide injury. Strangely enough, eriophyid mites are sensitive to the pesticide Sevin. Research performed by an entomologist with the Pennsylvania Department of Agriculture has shown that dimethoate is also very good for tip dwarf mite control. An advantage to using dimethoate is that it also controls spruce spider mites and scale insects as well. Joust for nurseries and Morestan for landscapes also give very good control of these mites.
Locust leafminers prefer to mine the leaves of black locust, but they have been reported from a few other trees as well. Outbreaks of this leafminer occur almost every year throughout the range of black locust, but seldom affect the same trees for more than a couple of years. Sometimes the damage is quite noticeable with acres of black locusts turning brown by mid summer. If trees are severely defoliated by locust leafminers and there are other stress factors present, then some trees may die. There is only one generation of locust leafminers per year. Adults overwinter and emerge in spring to feed. Eggs are laid in a mass and the tiny new larvae feed inside one leaf. Later the larvae divide and attack other leaves. One larva may mine several leaves before it matures. There are several parasites and predators of the locust leafminer which may explain why it does not maintain large populations in one area for a long time. There are several pesticides that can be used for locust leafminer control. Ornamentals and Turf Information Note No. 24 has additional control suggestions for leaf-feeding beetles.
Longtailed mealybugs suck out sap and excrete honeydew, a sweet sticky liquid. Most species of mealybugs lay eggs in a dense, waxy mass called the ovisac, but the eggs of the longtailed mealybug hatch almost immediately so that they appear to be born alive. The males pupate in a fluffy cocoon of wax. Thus the mealybugs, honeydew, male cocoons, and the ovisacs disfigure infested plants. Not only that, but as the mealybugs feed they inject their saliva into the plant. Some very sensitive plants are stunted, wilted, or even die when large numbers of longtailed mealybugs are feeding. Control of mealybugs is not easy. If only a few plants are infested, mealybugs can be removed with a cotton swab dipped in rubbing alcohol. The plant can then be washed with a mild soapy water emulsion to remove residual wax left by the mealybugs (about 2 percent soap, not detergent). The plants should be observed closely for a few weeks and new mealybugs removed as they appear. Some soaps are actually labeled for use as an insecticide for mealybug control on ornamental plants (Safer's, Citrusoap and Olympic). These soaps are available from various garden shops and plant centers. Malathion (2 teaspoonfuls per gallon of water) is also labeled for mealybugs. Plants can be sprayed thoroughly or dipped into the pesticide mixture. Malathion is a synthetic organophosphate insecticide of relatively low toxicity but it would be best to carry the plant outdoors (but in shade) for treatment. Imidacloprid (Merit for landscapes and interiorscapes, Marathon for commercial greenhouses and nurseries) is relatively non-toxic to humans but is a powerful systemic insecticide. Imidacloprid does not control mites. Ornamentals and Turf Insect Information Note No. 19 provides more information on mealybugs and their control.
Twobanded Japanese weevils remarkably feed during the day (most other weevil pests of ornamental plants feed at night), although they usually drop to the soil and remain motionless for a while when disturbed. This small, dark gray beetle usually has two irregular dark bands across the wing covers. Twobanded Japanese weevils cannot fly. Hence, their damage tends to be severe in small areas such as plant beds in a landscape where they probably arrived in an infested plant. Twobanded Japanese weevils attack almost any ornamental plant. Damaged plants appear tattered and unhealthy. Females lay their eggs in the folds of leaves that they tie together. The grubs feed on roots. Twobanded Japanese weevils are also unusual because they are resistant to several insecticides commonly used in the home garden, including Sevin, malathion and diazinon. Fortunately they are susceptible to Orthene insecticide which is labeled for home use and has the advantage of being systemic and not very toxic to humans. Commercial growers and landscapers can use a pyrethroid (Astro, Mavrik, Talstar or Tempo 2) for control. Because twobanded Japanese weevils drop from infested plants when disturbed, many can be trapped by carefully placing a cloth or large sheet of paper under the shrubs and then tapping or shaking the plant vigorously. The weevils can then be transferred to a container and destroyed. Ornamentals and Turf Insect Note No. 34 provides more information on the biology and control of twobanded Japanese weevils. Copies of this note should be available in each county Extension center in North Carolina.
Chinch bugs are beginning to create problems in St. Augustinegrass due to the hot weather. If you noticed discolored areas in a lawn, it may be caused by the feeding of this tiny insect. This insect has many generations per year and can persist throughout the summer, and in some hot years require multiple insecticide treatments.
Armyworms are showing up in a few locations. The dry weather earlier in the spring has caused many of them to seek the lush green of irrigated turf. Japanese beetles are laying eggs now so if you are using Merit or Mach2 for control, this is the time to apply those products. Green June beetles will begin to occur a little later in the summer. Mole cricket egg hatch is well underway and some of the earliest-hatched crickets already have grown significantly.
While traveling the state the past two weeks, I encountered a few specimens of yellow goatsbeard, also known as western salsify (Tragopogon dubius and several other aliases). Salsify is a member of the aster family, with a bright yellow flower on tall (2 to 3 feet in height) stalks and long, grass-like leaves. The most distinctive feature is the large (4 to 5 inches in diameter) dandelion-like seedhead. See Weeds of the Northeast (pages 164-165) for a complete description and photographs.
This weed can be particularly difficult to control in nursery crops and landscapes and is on the noxious weed list in several mid-western states. It is a biennial that germinates in the fall or early spring. Most herbicides labeled for use in nurseries and landscapes do not control this weed. Princep, Gallery, Surflan, Pendulum and other similar herbicides are not effective. The only herbicide that gave consistently good control in our trials was Predict (norflurazon). This can be used in field nursery crops but is not suggested for use in landscape plantings due to potential injury to ornamental plants and turf. Most non-selective postemergence herbicides (such as Roundup and Finale) will control salsify.
Sanitation is an important component of salsify control programs. The seeds only last 2 to 3 years in the soil. So, if you can prevent the weed from going to seed for two years you will have eradicated it from the field.
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Last modified on June 26, 2000 by Stephen J. Toth, Jr.