Contact: Diane Relf, Extension Specialist, Environmental Horticulture
Posted April 1997
When trying to identify a pest problem, check your resources. Most garden books, house plant guides and magazines, brochures from garden supply dealers, and Extension leaflets provide illustrations and descriptions of the more important pests of foliage and house plants. With experience, the various stages of the pests' life cycles become familiar, permitting more thorough diagnosis by the plant fancier. Advice and assistance can be obtained from garden store personnel, nurserymen, and local Extension agents.
APHIDS are small, soft-bodied insects that infest new shoots, stems, and leaves. There are many species, and they vary in color -- yellow, red, green, brown, gray, black -- often imitating the color of the plant part infested. Since they shed their "skins" as they grow, white, flaky specks drop onto leaves beneath aphid colonies -- a good clue to their presence on the plant. Aphids are sucking insects that excrete sugary honeydew. Honeydew appears as shiny, sticky droplets on foliage beneath aphid colonies in which black or brown sooty mold fungi may develop. Feeding damage causes stunting, curling, and distortion of the leaves and new growth.
SPIDER MITES are wingless, eight-legged relatives of insects that are too small to identify without a magnifying glass. They look like black pepper sprinkled on the undersides of the leaves. Feeding damage causes very fine stippling or yellow flecks on the upper leaf surfaces. They spin silk strands over their colonies on the leaf undersurface and also in the crotches of petioles and stems when infestations are severe. They attack a wide variety of plants.
MEALYBUGS are small (but larger than aphids), oval insects covered with white, powdery wax. More mature mealybugs have filaments of wax projecting from the body margin. They are also sucking insects and produce damage similar to aphids. Mealybugs tend to crawl into cracks, crevices, and crotches of petioles and twigs as well as along the veins of leaves and on the buds of new growth.
SCALE INSECTS include the brown, soft scale; the hemispherical scale; and the fern scale. The fern scale is very small, white, and elongate-oval as a male, and brownish, oyster-shell-shaped as a female. The other two are brown when mature and yellowish-green to tan when young and small. The brown, soft scale is oval and very flat. Hemispherical scale is what the name suggests -- a half-sphere. Both are soft scales and have a very extensive list of host plants. The fern scale is an armored scale with a white cover of wax. It is a pest of ferns, but also attacks numerous other hosts.
WHITEFLIES have two conspicuous forms: very small, white, waxy adults that are active fliers when plants are disturbed; and very small, round, sedentary, greenish-yellow nymphs attached by sucking mouthparts to the undersides of the leaves, often by the hundreds. They attack a wide variety of plants.
OTHER PESTS can cause damage occasionally, including cyclamen mites (especially on African violet and cyclamen), thrips, caterpillars, cutworms, and slugs. Some insects such as springtails and fungus gnats are a nuisance, but cause no damage, since they feed on organic matter in the growing medium.
(Originally published as "Control of Pests on Foliage and House Plants," by J. A. Weidhaas, Jr., Extension Entomologist, VPI & SU, in The Virginia Gardener Newsletter, Volume 9, Number 3.)