Answer: The control or remedy really depends upon the insect pest that is causing the damage. I can't really suggest a control until we know which insect is feeding on your hydrangea. Try capturing a few to have identified. In your region one likely suspect is the rose chafer, Macrodactylus subspinosus. The rose chafer sometimes feeds on hydrangea. When very abundant, this insect injures roses and many other shrubs and trees by the beetles skeletonizing the leaves. They also cause injury to the flowers, particularly white flowers, by feeding upon the petals and soiling them with excrement. Rose chafers breed most abundantly in sandy waste land but often occur in lawns; they appear each year about mid-June, and feed for about a month, though some of the beetles are present for 6 weeks. The females each lay from 24 to 36 eggs singly in the ground a few inches beneath the surface. They soon hatch and the young grubs feed upon the roots of grass and other plants, becoming full grown by late autumn when they go into the ground several inches to overwinter. The next April or May, they come near the surface and transform to pupae in earthen cells, and from 2 to 4 weeks later the beetles emerge. The adult beetle is yellowish grayish brown or clay colored and is a little over 1/3" (10-12 mm) long, with long sprawling legs. The larva is a white grub about 3/4" long when full grown.
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