Your trees and shrubs look great from a distance, but it’s important to inspect them up close every few weeks to catch insects and diseases before they progress too far and cause major damage. From mites to bagworms to beetles, insects can wreak havoc if not caught early. One particular kind of insect that is often overlooked are scale insects. These critters are so tiny that they don’t even appear to be insects. The look more like small bumps or a powdery coating. There are three common types of scale to look for on your trees and shrubs here in the Lubbock area – lecanium scale, eriococcus scale, and kermes scale. Each is slightly different, but all will harm your trees and bushes if not treated. The tree and shrub experts at Ashton Walden have put together this quick tutorial on what to look for to protect your trees.
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Look for Lecanium Scale on Dogwoods and Oaks
Lecanium scale are typically found on dogwoods and oaks. Lecanium scales suck sap from the leaves and twigs of trees and excrete honeydew, a sticky substance that coats objects underneath plants with a sticky sap. Sooty molds may also develop on the honeydew. Though they are tiny, they can cause significant damage to the host plant including stunting the plant growth and causing premature leaf drop and smaller flowers.
Lecanium scales, like most scale species have several forms. Female lecanium scales are 2 to 6 mm in diameter. When fully grown, female scales are rounded, reddish to dark brown and sometimes have a pale waxy bloom. Male scales are flying insects which are brown. Eggs are almost white and are so tiny they resemble fine pollen. New nymphs are called crawlers. Crawlers are flat, pale insects with conspicuous legs and antennae. Older nymphs are flat and brown. The legs and antennae become less noticeable as they mature. Males develop into a pupal stage that is a pale peach color and is covered by a translucent waxy coat. By mid-June, most of the eggs should have hatched and most of the crawlers should be on the leaves. Crawler sprays may be applied in early fall. Overwintered scales can be treated with dormant oils in late winter or early spring.
Eriococcus Scale or Azalea Bark Scale
Eriococcus scale are common on crape myrtle trees. One of the first signs of this scale is a black sooty mold coating that appears on the bark of the trunk of crape myrtles. Like with other species of scale, leaves and limbs may feel sticky because the insects secrete byproducts when they feed. The insects appear as white, waxy encrustations and can appear anywhere on the plant. Up close, the azalea bark scale-insect is white to gray in color. Larger female scales leave a pink liquid when crushed. Dozens of pink eggs may be hiding under some of the larger white scale covers.
For heavily infested plants, wash the trunk and reachable limbs with a soft brush and mild solution of dishwashing soap to remove most of the female scales and egg masses and make insecticide control more effective. Washing will also remove much of the black mold that builds up on the bark of infested trees. Then give us a call so we can come treat it with an insecticide or systemically.
Look for Dangling Branch Tips with Kermes Scale
Kermes scales are occasionally found on pin, white, bur, red, and other oak trees. If the branch tips of your oak are dropping off, it could be because of the insect Kermes scale. Adults are about ¼ inch in diameter, rounded and tan or brownish colored. They look similar to buds or other plant growth. Although the scales are brownish, they frequently appear blackish due to a coating of sooty mold. Sooty mold is a black fungus that grows on the honeydew, the partially digested and concentrated plant sap excreted by many scale insect species. Heavy infestations cause “flagging”, where the leaves on branch tips turn off-color, droop and often drop off. Infested trees have reduced growth and vigor.
Eggs hatch in September and October and crawlers move to overwintering sites on tree branches and trunks. Recommendations for timed sprays differ depending on the oak kermes species present, but insecticidal sprays are most effective on the crawlers before they form their protective shells for the winter.
Scale Treatment Strategies
Scale is most effectively treated with systemic products that are applied to the soil at the base of the tree and are taken up by the root system, working to control insects from the inside of the tree. A contact insecticide or horticultural oil can be sprayed on the scales, but is only effective when the timing coincides with crawler emergence.
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