Photo Gallery of Insects and Mites on Ornamental Plants
Slugs are soft, slimy, slender animals more closely related to clams and octopuses than insects. Slugs have stalked eyes and two small feelers. Some species grow to 3 or more inches long. Slugs are often attracted to odoriferous blossoms and to succulent leaves. They appear to be as sensitive in their sense of smell as humans. Slugs are most damaging to tender, young flower and vegetable plants in spring. They tend to stick with one plant, often consuming it entirely before moving on. Slug damage on foliage usually appears between the veins and on leaf margins. Small slugs rasp away the leaf or petal surface. Medium-sized slugs often eat holes. Large slugs consume whole leaves, petals and sometimes entire plants if the plants are small. They leave a silvery slime trail. Slugs are active at night and during cloudy, warm weather. During bright warm weather, slugs usually hide under boards, stones, debris or tunnel into the soil. At night or any time air temperatures are falling, slugs feed on decaying organic matter and succulent plants.
Slug populations can be reduced by eliminating their breeding and hiding places. Remove rotting boards, logs, pots and other debris from the area. Compost or destroy plant refuse and properly stack or store flats, boxes, etc. that provide shelter for slugs. Trim tall grass and weeds along fences and ditches in the vicinity of susceptible crops. Traps are useful in plant beds and gardens. Place 6 x 6 inch boards or other flat objects on the soil. Each morning remove the slugs from beneath the traps and destroy them. Of the baits used for slug control, metaldehyde is the most common. Deadline is the longest lasting and most resistant to weathering of the metaldehyde formulations according to research by Dr. Mike Parrella at the University of California. Any bait used will be much more effective if put under a board, pot or other object the slugs might crawl under. Ornamentals and Turf Insect Information Note No. 22 provides additional information on slugs and their management.
Carpenterworms are relatively large caterpillars that bore in the trunks of oaks. The adults are chunky moths that resemble tobacco hornworm moths, although carpenterworm moths are finely mottled and resemble bark speckled with lichens. The moths emerge in April and May, leaving their empty pupal skins protruding from the hole. Female moths lay 450 to 800 eggs on the bark on white oaks and other trees. Tiny caterpillars hatch and bore into the sapwood and eventually into the heartwood. Considerable sap sometimes flows from the tunnel opening. These caterpillars take two or three years to complete their development. For control, I suggest injecting an organic solvent into the hole with an oil can or something into the borer holes to kill the worms inside. Fingernail polish remover is a solvent that is relatively safe (I sure hope it's safe. My wife and daughters use a fair amount of it on their fingers!). It is not a violation of Federal and State pesticide laws to use a non-registered chemical as a pesticide (if fingernail polish remover were labeled to kill germs or repel chiggers or something, then it would be illegal to use it for carpenterworms). In the Midwest, trees infested with carpenterworms sometimes break off during storms. In the South, infested trees rarely break off due, but carpenterworms often infest a certain tree repeatedly. Such trees are called brood trees. Spraying infested trees year after year in the spring with Astro or with Dursban should eventually rid the tree of carpenterworms and should protect it from further infestation. There is additional information on the carpenterworm in Ornamentals and Turf Insect Information Note No. 27.
Cypress weevils have begun to emerge (or at least the cypress weevils from Cryptomeria stems we have been holding in the office have emerged). Surely this indicates that cypress weevils outdoors are now or soon will be emerging. The cypress weevil, Eudociminus mannerheimii, has recently been found damaging Cryptomeria in commercial nurseries and landscapes in North Carolina. This weevil was first described in 1836. It was next mentioned as the cypress weevil in 1904 by A. D. Hopkins who wrote that the adults kill the twigs of bald cypress by feeding on them. The grubs bore under the bark and cause defects in the wood as the trees can heal over the injury. The cypress weevil breeds readily in scarred and fallen cypress. In 1916, its known range extended from Louisiana to New York. Since New York is outside the range of bald cypress, the cypress weevil must have an alternative host (perhaps Atlantic white cedar). Except for lists in catalogs, we cannot find any publication on the cypress weevil since 1916. Until 1998, the only Eudociminus specimens in the North Carolina State University Insect Collection were two collected on September 1928 from Phelps Lake and two from White Lake collected on March 14, 1953. These were all associated with bald cypress. It is not certain whether the attacks on Cryptomeria are a once in a lifetime event or if Eudociminus is about to destroy the usefulness of Cryptomeria in the landscape. The cypress weevil is in the same group of weevils as the pales weevil, Hylobius pales, so it may have a similar life history. According to Insects of Eastern Forests, pales weevils overwinter as adults that may be active all winter (but in reproductive diapause) as adults in the forest litter or as larvae. This more or less agrees with what we have seen so far -- grubs are in the wood during the winter but some adults emerge almost immediately when the samples are brought inside. Adults feed on the stems where the bark is still green but not in the needles. Since the adults feed on the bark, I recommend spraying the bark with a pyrethroid such as Astro to protect against adult feeding and to kill them as they feed on the pesticide residue. For cypress weevil control, it would be good to should prune and destroy any dead wood, and cull and destroy any plants that are beyond help, and then consider spraying the shrubs to prevent further feeding. The shrubs should be sprayed now and again in late June or early July. I recommend Astro because it is labeled for borers in the nursery AND landscape, and because it is one of the pyrethroids that has a long residual life. Astro (Code 1547) is not a restricted use pesticide, and it has nursery, greenhouse, interiorscape and landscape uses on the same label.
In late May and June, persons from the Coast to the Piedmont have noticed birches that have stunted growth and aborted leaves. The stems and leaves of these plants have been infested with an eriophyid mite that has not yet been identified. Eriophyid mites are so small that they are virtually invisible. These mites are unusual in that they are shaped like cigars and have only four legs close to the mouthparts. There are many kinds of eriophyids. Some are vagrants and do little harm whereas others cause various galls, rusts, erineums, blasted buds and distorted growth. The mites on river birch appear to be in the same group of eriophyids as the blueberry bud mite, and the damage appeared more like broad mite damage to maples or to azaleas. Hemlock rust mites are often more abundant during cool, dry springs. Perhaps this spring has been cool and dry enough to encourage these mites as well. Eriophyid mites are susceptible to Sevin and other miticides including dimethoate. Since birch is one of the few ornamentals on dimethoate labels, dimethoate should give adequate control without harming river birch.
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 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.
Immature lady beetles are confusing because they do not resemble the adult stage that most people are familiar with from childhood. Immature lady beetles somewhat resemble six-legged gila monsters or alligators (but on a much smaller scale). When the larvae mature, they pass through a prepupal stage which attaches itself to the leaf or twig by the hind end. The insect then molts into the pupal stage that resembles a scale insect more than a lady beetle. Some days later the pupa molts and the wings expand and harden as the familiar lady beetle. Lady beetles are attracted to aphids for food. Sometimes the gardener notices the aphid damage from a distance (honeydew, sooty molds, stunted growth) and then examines the plant closely and discovers the lady beetle pupae (which look sort of like scales) and thinks the lady beetle pupae caused the problem. In the county Extension centers should be Ornamentals and Turf Insect Information Note No. 74 on lady beetles.
Maple bladder gall mites cause tiny wart-like growths on the tops of the leaves. Bladder gall mites are fascinating but microscopic eriophyid mites (only 2 pairs of legs) which overwinter on the bark of their host trees in a distinct overwintering form. In early spring as the new growth emerges, the overwintering mites crawl to the foliage and lay eggs from which hatch gall mites. The gall mites feed on the expanding leaves and induce the host tissue to form galls inside of which the mites feed and reproduce. The offspring of the gall mites are overwintering forms which leave the galls and crawl to the bark to spend the winter. Although the galls are alarming, they probably do no measurable harm to the tree. If control is desired, Eriophyid mites are sensitive to Sevin insecticide and to Joust or Morestan miticide. The best time to treat is in late fall after the trees have dropped their leaves. These mites are small enough that they can wedge into buds and other tight places so the treatment will have to be thorough for good control. One characteristic of gall mites is that they are exceedingly specific in their host plants. This mite will not spread to any other plants except maples.
Woolly alder aphids are noticed primarily in the spring on silver maple. They are called WOOLLY alder aphids because of the waxy fluff the aphids secrete to cover their bodies. This aphid sucks sap from the leaves and excretes honeydew, a sweet, sticky liquid that covers lawn furniture, walks, and the ground cover under the trees. Dark sooty mold fungi grow in the honeydew and further disfigure objects in the landscape. Bees, wasps and flies are attracted to the honeydew so that the landscape becomes a sticky, dark insect zoo. In late spring and early summer the aphids migrate to alder. Hence the name woolly ALDER aphid. Summer is spent feeding on the stems of alder. The migrating generation of woolly aphids is conspicuous because their fluffy, white wax shows up brightly as the aphids seem to float aimlessly along. In autumn the aphids migrate back to maple to lay eggs on the bark for next year's generations. The fall migrating generation of woolly aphids is not nearly as conspicuous as the summer generation, and most folks do not notice the aphids on the bark. The woolly alder aphid is not resistant to pesticides, but it may be difficult for amateur horticulturists to spray large trees. For long-term management, either eliminating alders in the neighborhood or changing species of shade tree is suggested. Ornamentals and Turf Insect Information Note No. 6 provides additional information on the biology and control of the woolly alder aphid.
Sycamore lace bugs feed on the lower leaf surface of sycamores and cause yellow or pale spots to appear on the upper leaf surface. This damage is somewhat like thrips injury and spider mite injury, but lace bug injury is coarser. If much feeding occurs, the leaves may become almost bleached out. Lace bugs also leave fly specks or excrement on the lower leaf surface (this is one way to tell lace bug damage from spider mite damage as spider mites do not leave any fly specks). Ornamentals and Turf Insect Information Note No. 39 provides more information on the biology and control of lace bugs. Sycamore lace bugs are relatively difficult to control if the tree is large. The pesticides listed in Ornamentals and Turf Insect Information Note No. 39 should provide adequate control if applied thoroughly. The population may resurge later in the season, because of eggs not killed by the first treatment.
It is time to think about postemergence control of nutsedges. In eastern North Carolina purple and yellow nutsedges are up and growing happily. If you have not already treated purple nutsedge with Manage or Image, then you better get to it. Yellow nutsedge can be treated with Basagran at this time also. In the mountains it is a little too early to treat with Basagran; wait until mid-June for the first application. Cannot tell which nutsedge you have? Consult Horticultural Information Leaflet No. 647. In the leaflet you will find guidelines for the identification and control of nutsedges. Follow all dose, timing and adjuvant guidelines to obtain optimum control. Of course, follow the label too! Each of these herbicides listed are registered for DIRECTED applications to woody ornamentals. That is, keep them off the foliage. Image can be taken up by the roots of many woody ornamentals and cause slight to severe injury. For that reason, I prefer Manage for purple nutsedge control. I prefer Basagran for yellow nutsedge control -- it works faster than Manage and is considerably less expensive.
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Last modified on May 31, 1999 by Stephen J. Toth, Jr.