Proper Pest Identification
Pest identification should be as accurate as possible. Management programs improve significantly with specific knowledge of the pest, its life cycle and behavior. Careful monitoring of species can enable you to detect subtle changes in a complex of pest species
Example: The displacement of leafminer species by the chrysanthemum leafminer, Liriomyza trifolii, can result in significant problems in leafminer control).
Generalized identifications can lead to control problems.
Example: Beet armyworm on scalding plants may not respond to insecticides used for other armyworm species that are more susceptible to commonly used insecticide products.
Pest identification should, at least, be as specific as the identification on the label of the pesticide to be used. If "caterpillars" are damaging an oak tree, a product for controlling "caterpillars" may be used unless the label specifically lists "tent caterpillars." Sometimes the actual common or scientific name of the pest is mentioned on the label, such as "forest tent caterpillar," signifying that the product can be used only for this specific pest. In other instances a more general name may be listed, such as "budworm," which requires some interpretation as to whether "spruce budworm" or "tobacco budworm" was intended.
The Federal Fungicide, Insecticide and Rodenticide Act (FIFRA) regulates the use of pesticides in the United States and specifies that they may be used only in accordance with the product label. Provision 2ee of FIFRA, however, allows the use of a product on ANY pest if the SITE for usage is listed on the product label. For ornamental plants, the site refers not only to the plant group or species, but also to the growing situation (greenhouse, interiorscape, nursery, etc.).
Damage Recognition
Arthropod pests produce characteristic plant damage related to the way they feed. These feeding symptoms are often easier to detect than the hidden pests themselves.
Chewing Insects (See illustrations of leaf damage)
Caterpillars, sawflies, grasshoppers, and beetle larvae and adults all have chewing mouthparts that can remove plant tissue. These pests chew holes in leaves, skeletonize leaves or defoliate plants. They may also tunnel in petioles and stems or consume them entirely. Recently damaged plant parts will have freshly damaged edges. Later the edges turn brown and die. Other evidence of chewing insects includes silk, found at some caterpillar feeding sites, or fecal material (excrement) in the vicinity of the damage.
When damage is found, always look for the arthropods responsible before applying pesticide. Beetles and grasshoppers often leave the area after feeding; caterpillars may finish feeding and pupate before they are detected.
Leafminer Flies
Serpentine leafminer
trail on leaf.
Photo by Bart Drees.
Leafminers, the immature stages or maggots of small flies, produce blister-like trails or blotches in leaves. The 1/8-inch yellow maggots have chewing mouthparts which tease apart the tissue between the outer layers of leaves. They feed inside leaves for several days before emerging to pupate on the ground. This resting stage lasts about 2 weeks. Adult leafminers look like tiny house flies (less that 1/8 inch long) marked with yellow and black patterns. Like house flies, they have lapping mouthparts. Female leafminer flies damage plants during egg laying by producing small, circular indentations, called stipples, on upper leaf surfaces.
Rasping Insects
Thrips
Thrips are tiny (1/32 to 1/16-inch long), slender bodied insects. Adults have hairy wings; immature thrips do not. With their sword-like mouthparts, adult and immature thrips feed by slicing or rasping open plant cells on the surfaces of leaves, buds, flowers or fruits. They then suck the contents out of the ruptured cells. On mature plant parts, their feeding causes tiny silver streaks which are rows of empty, dead cells. If plant parts are still growing when attacked by thrips, the damaged surface cells stop growing and undamaged cells continue to develop around them. This causes deformed plant parts. Occasionally, thrips are no longer present when these deformities begin to show. Thrips will also feed on pollen, and some thrips species prey on other insect and mite pests. Anticipate massive thrips migrations into landscape areas when nearby alternate hosts, such as weeds and wildflowers, begin to mature and die.
Sucking Insects (See illustrations of leaf damage)
Cornicles on a cotton
or melon aphid.
Photo by Bart Drees.Aphids, whiteflies, mealybugs and scales (all usually less that 1/8-inch long), as well as the larger plant bugs and stink bugs, are sucking insects.
Aphids can be identified by the two "exhaust pipes," called cornicles, on the ends of their abdomens, and they may or may not have wings.
Whitefly immatures look like scale insects on the undersurfaces of leaves, but adults can fly when disturbed.
Mealybugs are covered with white, waxy ornamentations and crawl along the surface.
Scale insects attack leaves and stems, and look like variously shaped domes attached to the plant.
All of these sucking insects feed by puncturing plant parts with their long, straw-like mouthparts and removing sap, causing plant stress and sometimes making plants appear wilted. Some of these pests inject toxic salivary secretions into plant tissues as they feed, which causes extensive yellowish or reddish areas or dead areas. Damaged or dead leaf spots sometimes fall off the plant, leaving holes that might be mistaken for chewing insect damage. Sucking insects also cause plant deformities similar to thrips damage on growing plant parts. Some mealybug species feed below the soil on roots.
Aphids, whiteflies, mealybugs and scale insects remove more sugar-rich fluids from plants than they need, and eliminate this sticky material, called honeydew, around feeding sites. A fungus called sooty mold grows on leaves covered with honeydew. This black mold decreases the aesthetic value of plants and stresses them further by blocking the sunlight needed for photosynthesis. Some sucking insects can transmit plant diseases. Preventing diseases by attempting to control potential vectors is extremely difficult.
Piercing-sucking Arthropods
Mites
Spider mites, the tiny (1/32-inch long) eight-legged relatives of insects, produce
Two-spotted spider mite.
Photo by Bart Drees.
damage similar to that of thrips. However, they use their mouthparts to first pierce plant cells and then to suck out the contents. Spider mite damage gives a stippled appearance to leaf surfaces, causing leaves to appear bronzed. Infestations always begin on the undersurfaces of leaves. Breeding infestations often can be identified by the whitish cast skins of developing mites. Mites also produce silken webbing around infested plant parts. Outbreaks often occur during drouth stress or after the use of broad spectrum insecticides that allow mites to survive while eliminating their natural enemies. Repeated applications of miticides should be made after spider mites are first detected, since the egg stage is usually unaffected.
There are other mite species that attack ornamental plants. Cyclamen, broad and eriophyid mites can produce various plant deformities, but they do not produce the silken webbing or the bronze stippling characteristic of spider mites. They are also even smaller and harder to detect than spider mites, and may only be seen with a hand lens or microscope.
Unidentified Pests
Many of the tiny insect and mite species seen in the greenhouse are not pests. They are likely to be natural enemies (predators or parasites) of pests which I refer to as the "free help" in taking care of real pest problems. Other arthropods may be just casual invaders passing through the area and uninterested in plants other than as a place to rest. The effort invested in making correct pest identifications can save you money by helping to eliminate unnecessary pesticide applications.
If the cause of a plant health problem is undiagnosed, control measures are often futile. Plant deformities or irregular growth may be caused by insect pests that have already left or ones that are difficult to identify, as well as by disease, improper watering or fertilizing, toxic compounds and other problems. County Extension agents and specialists can help in identifying the causes of plant damage. Or, specimens can be submitted to the Texas Plant Disease Diagnostic Laboratory for identification (for a nominal fee). If you don't know, don't treat, get help!
PRINTABLE VERSION 
Related
Source: Pest Management Alternatives for Commercial Ornamental Plants, Bastiaan M. Drees, published by the Texas Association of Nurserymen, 1992
Selected references for pest identification
Baker, J. R. (ED) 1980. Insects and related pests of shrubs, some important shrubs, some important, common, and potential pests in the Southeastern United States. North Carolina Experiment Station, Dept. of Agric. Information, North Carolina State University, Raleigh, North Carolina 27607.Baker, J. R. (ED) 1982. Insect and related pests of flowers and foliage plants, some important, common and potential pests of North Carolina. North Carolina Experiment Station, Dept. of Aric. Communications, North Carolina State University, Raleigh, North Carolina 27650.
Baker, J., 1986. "Insects found on yellow sticky cards." N.Ca. Flower Growers Bull 30(1):10-13.
Benyus, J. M. 1983. Christmas tree pest manual. USDA, Forestry Service, North Carolina Experiment Station, Superintendent of Documents, U. S. Gov. Printing Office, Washington, D.C., 20402.
Gill, R. J. "Photo recognition key to the white flies and scale insect families of California". Scale and White fly key #1. State of Calif. Dept. of Food and Agric. Environ. Monitoring and Pest Management, 1220 N. St., Sacramento, CA. 95814.
Gill, R. J. "Color-photo and host keys to California white flies". Scale and White Fly Key #2. State of Calif. Dept. of Food and Agric. Environ. Monitoring and Pest Management, 1220 N. St., Sacramento, CA. 95814.
Gill, R. J. "Color-photo and host keys to the mealy bugs of California". Scale and White fly key #3". State of Calif. Dept. of Food and Agric., Environ. Monitoring and Pest Management, 1220 N. St., Sacramento, CA. 95814.
Gill, R. J. "Color-photo and host keys to the soft scales of California". Scale and White fly Key #4. State of Calif. Depart. of Food and Agric., Environ. Monitoring and Pest Management, 1220 N. St., Sacramento, CA. 95814.
Gill, R. J. "Color-photo and host keys to the armored scales of California". Scale and White fly Key #5. State of Calif. Depart. of Food and Agric., Environ. Monitoring and Pest Management, 1220 N. St., Sacramento, CA. 95814.
Johnson, W. T. and H. H. Lyon. 1988. Insects that feed on trees and shrubs. Second edition. Cornell University Press, 124 Roberts Place, Ithaca, NY. 14850. 556 pp.
