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Sycamore scale (Stomacoccus patani) is remarkably small -- approximately 1/16 inch long -- so it is most often recognized by its feeding damage rather than the scale insect itself.

Pest of the Month: Sycamore Scale

By Jodi Zirbel


What does it look like?

Sycamore scale (Stomacoccus patani) is remarkably small — approximately 1/16 inch long — so it is most often recognized by its feeding damage rather than the scale insect itself. Using a high-powered lens, scales can be found on the underside of leaves. Another identifier is the waxy secretion, which could contain eggs and nymphs, that they leave behind on leaves and tree bark.

Scales progress through several life stages including adult, egg and at least two instar stages. Eggs are light yellow or white, and are found in a cottony, white mass on leaves and bark. The first instar stage, emerging from the eggs, produces crawlers. After feeding, these crawlers lose their legs and antennae, turning into a nymph state that settles overwinter.

From the second instar stage, females remain swollen and legless until the adult emerges. Males, however, go into a third or late-instar stage before emerging as adults. Although males initially lack appendages, the late-instar stage produces a nymph with both legs and antennae. Only mobile for a brief period of time, the nymph then goes into a cocoon state, ultimately producing the adult male scale.

Yellow or orange in color, adults are elongated, often resembling wingless thrips. Males are only half as long as females, but both have distinct body segments, legs and long antennae.


Host material and range

Found currently in California, Arizona, Nevada and New Mexico, sycamore scale affects the native California sycamore, Oriental sycamore and the London plane tree. It has not yet been found to inhabit or feed on the American sycamore tree, found primarily throughout the eastern United States.


Current threat

The most obvious injury is the spotting of leaves caused by their feeding. In fact, very often sycamore scale is confused with leaf spot disease because the signs are so remarkably similar. The scales feed on the underside of leaves, as well as leaf buds and young bark from twigs and branches. This feeding causes stress to the tree, which often results in premature leaf drop or distorted leaves, and twig dieback and bark loss. Stressed trees may also be more prone to other diseases such as sycamore anthracnose and powdery mildew.


Prevention tips

Healthy trees are better able to withstand pressure from sycamore scales, so be sure sycamore trees are properly irrigated and free from stress. In addition, if sycamore scale was an issue the previous year, consider a spray treatment during bud break, which is the best time to perform an application. If you’re unsure about the previous year’s pest history, check for sycamore scale eggs and nymphs.


Treatment tips

First instars emerge during bud break and are the most susceptible to insecticides, therefore will net the best results in terms of treatment. Chemical controls can include either spray applications or micro-injection treatments. Look for insecticidal treatments that contain imidacloprid or dinotefuran. Other treatment techniques can include the application of horticultural oils or insecticidal soaps — or a combination of these with a chemical treatment.


What can you do?

Inspect trees close to bud break — usually in January — to determine if a chemical treatment is necessary. Studies have indicated when sycamore scale numbers are reduced during a bud break application the surviving scales can’t produce high numbers of crawlers during future instar stages, further declining the population.


Jodi Zirbel is with Epic Creative, Wis. Article provided by Mauget, a leader in micro-injection and micro-infusion tree care. Contact Mauget or visit www.Mauget.com to learn more about sycamore scale.

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