Cottony scale (Pulvinaria spp.)
European fruit lecanium (Parthenolecanium corni)
Excrescent scale (Eulecanium excrescens)
Pest description and crop damage Mature scale are up to 0.2 inch across, reddish brown, and rounded, resembling small helmets or bumps on branches, stems, and the underside of leaves. Adult female cottony scale produce copious amounts of white cottony filaments containing eggs in summer. The crawlers are flat, oval, and pinkish brown. Chemical management should target the crawler stage. Scale insects are closely related to aphids, mealybugs, and whiteflies. Like these insects, they also have piercing-sucking mouthparts. Severe infestations can kill twigs and may have reduced nut size and kernel fill similar to aphids. Large quantities of honeydew are produced, which causes growth of sooty mold fungus. Sooty mold fungus can impede photosynthesis and severely devitalize plants and retard growth.
Biology and life history Lecanium scale overwinters as an immature scale on twigs and branches. They resume feeding in the spring, and eggs are laid underneath the scales in May to June. The eggs remain under the scales until hatching in early summer. The emerging young scales, called "crawlers," migrate to the undersides of leaves to feed. Young scales also can be dispersed by wind, rain, irrigation, or by the movement of people and machinery. After 4 to 6 weeks on the leaves, the young return to the stems and twigs to feed, mate, and overwinter. There is one generation per year.
Parasitoids attack scale and scale outbreaks may be the result of broad-spectrum insecticide use. Monitor biological control by scouting for small emergence holes on the mature females where the parasitoid has chewed its way out of the scale host.
Home orchardists: Scale can be rubbed off plants by hand with a glove or toothbrush. Major infestations can be pruned off. Tanglefoot, "stickem," or a similar adhesive can be applied around infestations of adult scales to catch the crawler stage. As with aphids, avoid excessive nitrogen fertilizer or water applications, as this favors increases in the populations.
Management-chemical control: HOME USE
Applications are directed at crawlers that appear in June or early July. Take precautions when treating scale to avoid disrupting pollinators that may actively foraging on honeydew.
- acetamiprid-Do not apply until after trees have flowered or when bees are actively foraging. Do not make more than one application a year. PHI minimum of 7 days.
- azadirachtin (neem oil)-Some formulations are OMRI-listed for organic use.
- bifenthrin (as a mix with other ingredients).
- imidacloprid (as a mix with other ingredients).
- insecticidal soap-Some formulations are OMRI-listed for organic use.
- lambda-cyhalothrin (as a mix with other ingredients).
- plant-derived essential oils-Some formulations are OMRI-listed and have shown efficacy against scale.
- pyrethrins (often as a mix with other ingredients)-Some formulations are OMRI-listed for organic use.
Management-chemical control: COMMERCIAL USE
- acetamiprid (Assail 70WP) at 0.57 to 1.0 oz/100 gal water (2.3 to 4.1 oz/a). PHI 14 days. REI 12 hr. No more than 4 applications per season.
- buprofezin (Centaur WDG) at 34.5 to 46.0 oz/a. No more than one application per season. PHI 60 day. REI 12 hr.
- clothianidin (Belay) at 3 to 6 oz/100 gal water. Use the low rate for smaller infestations or smaller trees. Apply no more than 0.2 lb ai /year. PHI 21 day. REI 12 hr.
- imidacloprid (Admire Pro) at 1.4 to 2.4 oz/a. Generic labels available. PHI 7 days. REI 12 hr.
- pyriproxyfen (Esteem 35 WP ) at 3.2 to 4 oz/100 gal water (13 to 16 oz/a). Do not apply more than twice per season. PHI 21 day. REI 12 hr.
- spirotetramat (Movento) at 6 to 9 oz/a. Minimum reapplication interval is 14 days. PHI 7 day. REI 24 hr.