Answer: Although damage may be unsightly, it is usually not fatal to the tree. Even if total browning occurs in one season, it is seldom severely damaging, but if it should occur two or three years in a row, it could be serious to the health of the tree, especially trees that are not well established. Natural enemies, including several parasites, exist, and one pupal parasite looks to be especially effective in reducing the populations of this insect.
With some ornamental pests, such as this one, it is a judgment decision on the part of the plant owner whether to engage in some type of control measure, or to let nature take its course. If management of the pest is desired one of the following insecticides may be used for control of the imported willow leaf beetle (listed in order of increasing toxicity to natural enemies and other non-target organisms): Bacillus thuringiensis var. tenebrionis* (Btt), insecticidal soap, spinosad, carbaryl (Sevin) or cyfluthrin/imadacloprid. One spray should be applied in mid to late May or early June (192-448 GDD)**. GDDs (growing degree days) are a way of measuring temperatures and are associated with insect activity. Your local radio station may make this information available. Careful observation will determine if more than one spray is necessary. Btt, insecticidal soap and spinosad are considered less toxic pesticides. Other pesticides such as carbaryl or cyflythrin/imadocloprid are more broadly toxic, and might adversely affect populations of natural enemies or pollinators.
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