The following is information on control of common adelgid insects in Delaware landscapes.
The Eastern Spruce Gall, Cooley Spruce Gall and Hemlock Woolly Adelgids all over-winter as immature females and are vulnerable to control treatments during the late months of the year. The product of choice with smaller plants is the use of horticultural oils or soaps when good coverage can be achieved. Remember to target sprays onto only the most recent growth or terminal twigs and buds where the adelgids are located. Heavy populations of HWA on large hemlocks are best controlled with an imidachloprid (Merit) treatment.
Hemlock woolly adelgid & treatment limitations:
The autumn season is an excellent time to control this hemlock pest, if no controls have been applied to date. The adelgid nymph is exposed on the underside of new growth, at the base of individual needles from May through early November. By November, it begins to cover itself with the white, wooly wax. Information from the US Forest Service indicates that hemlocks that have experienced over 50% needle loss from the adelgid will not recover in subsequent years (even if treated). Therefore, it is important that treatments be made when the needle loss is below 50% if hemlocks are to recover or survive. Fall treatments of insecticidal soaps, horticultural oils, or Merit are very effective. Excellent spray coverage is required with soaps or oils. When using Merit drenches, be certain adequate soil moisture exists.
Hemlock woolly adelgids. Photo by John A. Weidhass, Virginia Polytechnic Institute and State University, Bugwood.org
Information from Steven K. Rettke, Ornamental IPM Program Associate in the September 17, 2009 edtion of the Plant & Pest Advisory, Landscape, Nursery & Turf Edition, from Rutgers University http://njaes.rutgers.edu/pubs/plantandpestadvisory/2009/ln091709.pdf