Calico Scales About to Hatch!

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Calico scale, Eulecanium cerasorum, was accidentally introduced to California from Asia in the 1920s. It has now become established in many eastern and north-central states. Calico scales attack maples, honeylocust, hackberry, dogwood, walnuts, stonefruits, sweetgum, and many other tree species. Calico scale adults and immatures feed on phloem. They produce copious amounts of honeydew, coating underlying leaves and surfaces and promoting sooty mold growth. Heavy infestations can lead to loss of tree vigor, foliage distortion, and branch dieback.

Calico scales on dogwood.

Calico scales on dogwood. Photo: SD Frank

There is one generation per year. The scale overwinters as a second instar nymph on the bark. Each female can produce up to 4,600 eggs. Once eggs are produced the female shrivels and dies, becoming darker brown. Crawler emergence is happening soon. I have seen adults swollen with eggs in Raleigh and in the mountains this week. The tiny crawlers settle and begin feeding on foliage, where they remain through mid-October and then migrate back to the bark to overwinter.

There are many natural enemies that feed on calico scales but on street trees, nurseries, and other stressful locations the scales will still thrive. Applications of insecticidal soap can reduce populations especially during crawler emergence. Insect growth regulators like pyriproxyfen and buprofezin can also be effective if needed.