Tiny Broad Mites Can Cause Big Damage

broad-mite-photo-by-alton-sparksBroad mites (Polyphagotarsonemus latus) can be a major problem on pepper in Florida. This species has a worldwide distribution and can affect a large number of hosts including vegetables such as basil, eggplant, green beans, potato, and a variety of fruits and ornamental plants. This destructive pest attacks terminal leaves and flower buds and causes them to become malformed. Broad mite feeding distorts plant tissue, causing leaves to become hardened, thickened and narrow, giving them a “strappy” appearance. The blooms abort and plant growth is stunted when heavy pressure is present. Broad mite injury can be confused with herbicide injury, nutritional (boron) deficiencies, or physiological disorders.

Mites are usually seen on the newest leaves and small fruit. Leaves turn downward and turn coppery or purplish. Internodes shorten and the lateral buds break more than normal. Malformed terminal buds and stunted growth often is a telltale sign that broad mites are present. Broad mites are extremely tiny and are difficult to see without a 10x or stronger hand lens. The mites may crowd into crevices and buds. Mites prefer the shaded side of fruit and the underside of leaves, which usually faces the plant, so scouts must be diligent and carefully inspect affected plants to detect these tiny creatures.

Survival And Spread
The broad mite has four stages in its life cycle: egg, larva, nymph, and adult. Adult females lay about five eggs per day over an eight- to 13-day period and then die. Adult males may live five to nine days.
The eggs are about 0.08 millimeter (mm) long and are colorless, translucent, and elliptical in shape. Eggs hatch in two or three days and the larvae emerge from the egg shell to feed. Larvae are slow moving and do not disperse far.

After two or three days, the larvae develop into a quiescent larval (nymph) stage. Quiescent female larvae become attractive to the males, which pick them up and carry them to the new foliage.
Female mites are about 0.2 mm long and oval in outline. Their bodies are swollen in profile and a light yellow to amber or green in color. Males are smaller (0.11 mm) and faster moving than the female.
Males and females are very active, but the males apparently account for much of the dispersal of a broad mite population in their frenzy to carry the quiescent female larvae to new leaves. When females emerge from the quiescent stage, males immediately mate with them. Broad mites are known to use insect hosts, including bees and whiteflies, to move from plant to plant.

Management Methods
While a number of products such as Agrimek (abamectin, Syngenta) and Oberon (spiromesifen, Bayer CropScience) are labeled for control of this pest, sulfur and insecticidal oils or soaps may also be effective. Due to short life cycles, frequent repeated sprays may be necessary to obtain control.

Biological control agents including several species of predatory mites have been used successfully to control broad mites in field and greenhouse situations.

By Gene McAvoy, Regional Vegetable Specialist IV, University of Florida/IFAS