Answer: Many scale species are pests of holly. Scales are unusual insects in appearance. They are small and immobile, with no visible legs. Scales vary in appearance depending on age, sex and species. They feed on sap by piercing the leaf or stem with their mouthparts and sucking. They are typically found on the undersurfaces of leaves and look like small brownish or grayish bumps. Some species may be found on the branches as well. Adults are relatively protected from insecticides by their waxy covering. Their immature forms, called crawlers, are susceptible, however.
Control: Light infestations of scale can be scraped off by hand. For heavier infestations, spray with a horticultural oil (Bonide All Season Spray Oil, Ferti-lome Scalecide, Green Light Horticultural Oil Spray, or Ortho Volck Oil Spray) in the early spring to kill adults. Oil should be applied before new growth begins to kill adults and eggs.
Monitor the crawler emergence with sticky cards, double-faced tape wrapped around a branch, or by putting an infested shoot or leaf into a baggie and watching for crawler movement. Crawler activity often coincides with the flush of new plant growth in the spring. However, some scale species may have overlapping generations with an extended crawler emergence period, such as along the coast. Spray with horticultural oil in the spring after the plants have begun growing and the danger of cold weather has passed. Repeat this application after 10 days to better control the crawlers, adults and eggs by smothering them. Horticulture oil may be sprayed when temperatures are between 40 and 85 degrees.
Avoid using insecticides unless the plant is very valuable and in serious danger from scale. Insecticides will often kill the naturally occurring predators of scale. If insecticides are going to be used, spray when crawlers are observed. Insecticides labeled for homeowner use against scale crawlers include acephate (Ortho Japanese Beetle Killer), malathion (Ferti-lome Mal-A-Cide, or Hi-Yield Malathion Insect Spray), cyfluthrin (Bayer Advanced Garden Power Force Multi-Insect Killer), and carbaryl (Sevin 50WP or Ferti-lome Carbaryl Spray). As with all pesticides, read and follow all label instructions and precautions.
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