Common Plant Pests

Bennett Joffrion, Fletcher, Jr., Bobby H., Razi, Sam S.  |  10/22/2007 8:10:52 PM

Aphids on a Rose

Asian cycad scale, family Diaspididae, an armored scale.

Cottony cushion scale, family Margarodidae.

Aphids are winged or wingless insects with pear-shaped bodies that may be any color or even multi-colored. They are separated from other closely related insect by the pair of cornicals on the end of the abdomen. Aphids are typically found on new or tender growth. Damaged foliage may be discolored or yellow, sometimes twisted or distorted and sometimes appear as if infected by a virus. Ants and sooty mold may be present.

Natural management. Lady beetle (ladybug) adults and larvae, lacewing adults and larvae, syrphid fly larvae, parasitic wasps and some fungi.

Other management tools. Prune infested plant parts or flush with high water pressure from a hose; apply insecticidal soaps, ultra fine or horticultural oils; or drench with systemic products that contain imidaclorpid or acephate.

Scale Insects

Scales belong to several families (see photos). They are a complex and diverse group of insects. They vary in size from 1/16 inch to ¼ inch in diameter, and the shape, color and wax density and covering are very different between families.

The two body types are armored and soft scales. The armored scale body is hidden under a waxy shell-like covering. Some families of scales are stationary, and others move throughout their life cycle. Scales can be found on all parts of the plant depending on the kind of scale, and some are moved around by ants to protect them from predators, parasites and cold weather.

Soft scales excrete honeydew (sugary excretion) and can have varying amounts of wax secretions on the body, from the powdery wax of mealybugs to the thick, heavy coverings of the magnolia and wax scales. Discoloring of the foliage as well as honeydew or sooty mold may be found on the foliage and stems of the plants. Again, ants are protectors of the scales because they milk them for the honeydew secretions. Crawler is the term given to the live-born or recently hatched scales. This is the only stage of some families of scales that have legs. This is by far the most vulnerable stage of the scale’s life cycle to manage.

Natural management. Natural predators include lady beetles (ladybugs), lacewings and parasitic wasps.

Other management tools. Options include sprays with ultra fine or horticultural oils, insecticidal soaps or a spray with an insecticide recommended for scale control or a drench with a product containing either acephate or imidaclorpid. All scales possess a waxy protection. To manage the population requires the addition of some type of spreader sticker to assure contact with the scale when sprays are required. If spreader sticker is not used, the water with the insecticide will bead up and roll off the scale without providing the contact necessary for management of the populations.


Adults look like tiny white moths on plants. They take flight when the leaves are disturbed. Whiteflies lay their eggs on the underside of the foliage. The nymphs (immatures) are oval, flat, transparent-to-greenish and are found on the underside of the foliage. In the pupal stage, eyes may be detected and are usually red. Ants and sooty mold may be present because of excretions of honeydew from the nymphs.

Natural management. Controls include fungi (most effective in humid weather), parasitic wasps and lady beetles.

Other management tools. Use sprays with ultra fine or horticultural oils, two to three times at 10-day intervals, or sprays with insecticidal soaps on the same schedule. Where necessary, sprays with a spreader sticker and an insecticide containing either imidaclorpid or acephate should be applied, or they may be drenched on the roots.


Caterpillars are the larval form of butterflies and moths. They eat the foliage, causing skeletonized leaves, notched foliage or defoliation of the plants. Greenish fecal pellets may be observed on the foliage or under the infested plants.

Natural controls. Wasps, birds, parasites, stinkbugs, big-eyed bugs, lizards and pathogens.

Other controls. Remove by hand. Stinging caterpillars can be shaken off plants and crushed or mashed. Sprays of Bacillus thuringiensis kurstaki or aizawai or Spinosad are best sprayed when caterpillars are small. When needed, one of the available pyrethroids (cyfluthrin, permethrin, deltamethrin) plus liquid soap is effective (Louisiana Insect Pest Management Guide).


These foliage-feeding larva look like caterpillars but are actually sawflies. They can be separated from caterpillars by looking at the number of legs on the abdomen. Caterpillars have one to four legs on the abdomen while sawflies have one on each segment of the abdomen. Caterpillars have a series of simple eyes on each side of the head while sawflies have only one simple eye on each side.

Natural controls. Same as caterpillars.

Other controls. Any number of insecticides are effective management tools (Louisiana Insect Pest Management Guide).

Plant-feeding mites

Mites are tiny (¹/32-inch) red, yellow or greenish with oval bodies. They may have spots. Some species spin webs on the foliage of infested plants. Mites reproduce rapidly in hot, dry weather. Injury to plants looks like light-colored dots, giving the leaves a dull, gray-green, stippled appearance. This appearance is caused by their shallow feeding.

Natural controls. Lady beetles, predatory mites.

Other management tools. Flush with water, spray with soaps or ultra fine or other horticultural oils. Where populations are heavy, two to three applications at 7-day to 10-day intervals may be necessary. In some situations, the use of a miticide plus horticultural oil may be required to obtain effective management.


Thrips are tiny (1/32-inch) winged insects that rupture the cells on leaves, buds and flower buds to lap up the exuding fluids. This injury causes browning on the flowers and poor bloom. The damage to the foliage is the same as by mites, producing a stippling and grayish cast on the leaves. Occasionally, leaves become distorted and curl and, on occasion, drop off.

Natural controls. None identified.

Other management tools. Apply horticultural oils, insecticidal soaps and the insecticides imidaclorpid, acephate or malathion. The insecticides are best used with oils.

Mole Crickets

Mole crickets are 1½-inch-long, velvety brown insects that feed on turf grass. Their front legs are flattened and adapted for burrowing. Mole crickets affect all grasses but prefer bahiagrass and bermudagrass. Injured turf may be spongy and thinning, with ¾-inch tunnels running through the turf. This tunneling opens the soil and dries out the roots of the turf grass. Infestations are likely to begin in sandy areas and move out from there. To check for an infestation of mole crickets, use two tablespoons of lemon soap in one gallon of water and drench an area where tunneling is observed. This treatment will force the crickets to the surface for proper identification.

Natural controls. Parasitic wasp (Larra bicolor), red-eyed fly (Ormia deplete), insect-parasitic nematodes, fire ants and birds.

Other management tools. Baits can be made and used early in the season once initial tunneling is observed. Spot treat early infestations with materials listed in Louisiana Insect Pest Management Guide.

Chinch Bugs

Adult chinch bugs are 1/5 inch long, black with white patches on the wings. Young nymphs are smaller and reddish. Chinch bugs feed on St. Augustine grass, often in stressed areas in full sun or near pavement. Populations can develop quickly in hot, dry weather. Injured turf appears yellow.

Natural controls. Big-eyed bugs, earwigs and fire ants.

Other management tools. Avoid high fertilizer rates. Maintain St. Augustine grass at height of 3 inches in sun and 4 inches in shade. Water turf under dry conditions, which are favorable to chinch bugs. Use chinch bug-resistant varieties when possible. Spot treat infestations with insecticidal soaps or other materials labeled for chinch bugs (Louisiana Insect Pest Management Guide).

Red Imported Fire Ants

Fire ants vary in size. They can inflict a vicious sting that will form a white pustule. This will burn initially and then itch. Avoid scratching to prevent infection. Mounds in the yards can be damaging to lawn mowers, and accidentally disturbing them can be dangerous to pets, children and other wildlife. Individuals who are allergic to insect bites or stings can be seriously injured. Populations in a mound can vary from a few ants when beginning to 100,000-plus ants in an established colony.

Natural predators. The decapitating phorid flies and the disease thelohania.

Other management tools. Effective fire ant management can be achieved with baits. Be sure the bait is dry and fresh. Depending on the material used, the time required for results will vary. Contact materials work quickest; growth regulators the slowest. Area-wide community programs work best with only two treatments a year. Contact your local LSU AgCenter extension agent for more information on this program. Do not apply when ground is wet or rain is eminent. Do not disturb the mound. Follow label directions according to the material used (Louisiana Insect Pest Management Guide).

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