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Abstract
Both greenhouse and field studies have shown that it is the combined stress of drought and infestation by the hemlock woolly adelgid that causes death in eastern hemlocks. In three separate greenhouse studies it was found that the presence of adelgids alone did not cause the death of the plants over a period of 1, 2 or 5 years respectively, if they were well watered and received sufficient nutrients. Another greenhouse study found that drought hastened the death of infested hemlock seedlings. This was reflected in the rapid fall in the rate of chlorophyll fluorescence. In this study the effect of the adelgids alone was not sufficient to cause the death of the seedlings, however the added stress of drought did result in the death of the seedlings, within a period of a few weeks.
Parent Publication
Citation
Sivaramakrishnan, Saroj; Berlyn, Graeme P. 2000. The role of site conditions in survival of hemlocks infested with the hemlock woolly adelgid: amelioration through the use of organic biostimulants. In: McManus, Katherine A.; Shields, Kathleen S.; Souto, Dennis R., eds. Proceedings: Symposium on sustainable management of hemlock ecosystems in eastern North America. Gen. Tech. Rep. NE-267. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northeastern Forest Experiment Station. 201-204.
