Buckeye Yard and Garden onLine

The calico scale is a globular, blackish-brown soft scale that is about 1/4" in diameter. It is easy to recognize because of the distinct rows of squarish, white patches on the back. Its life cycle is similar to European fruit lecanium. The scale has one generation per year and overwinters on twigs as partially developed nymphs. As spring progresses, the nymphs will feed, molt, and mature into globular adults. In late spring to early summer, eggs are laid and the hatching nymphs migrate to the undersides of leaves. In late summer to early fall, the nymphs molt to second instars and move from the leaves to stems, branches, and the trunk where they overwinter.

The calico scale has numerous hosts that can support its growth and development including: honeylocust, maple, magnolia, sweetgum, ornamental fruit trees and dogwood. Calico scale is seldom a direct killer of established landscape trees; however, heavily infested trees may lose enough sap to cause them to succumb to other stress related factors. The large quantities of honeydew can be colonized by sooty molds giving the host an unsightly, black appearance. If suppression is deemed necessary, applications of the systemic insecticide imidacloprid (e.g. Merit) targeting first instar crawlers will provide effective control. Although it is not typically the right time of year to treat infested trees now because it may take up to six weeks to get the insecticide up into the foliage where the crawlers will be feeding, there may be some impact on the population. First instar crawlers hatch from eggs when the GDD reaches 748. Additionally, trials in Ohio have indicated calico scale can be managed using soil drenches of neonicotinoid systemic insecticides such as imidacloprid (e.g. Merit, Marathon), clothianidin (e.g. Arena), and dinotefuran (e.g. Safari) made from September into November.

For more Information, see:

• Calico scale insecticide trial
• Calico scale alert