I receive several phone calls a month asking me “What is attacking or killing our beautiful hemlocks?” The good thing is; it’s not a disease. The bad thing is; it’s an insect or more correctly an Adelgid. It was introduced into the United States in 1951 around Richmond, Virginia. By 2005, it was established in portions of 16 states from Maine to Georgia, where infestations covered about half of the range of hemlock. Areas of extensive tree mortality or decline are found throughout the infested region, but the impact has been most severe in some areas of Virginia, New Jersey, Pennsylvania and Connecticut.
Hemlock decline and mortality typically occurs within 4 to 10 years of infestation in the northern range, but can occur in as little as 3 to 6 years in the southern range. Other hemlock stressors, including drought, poor site conditions, and insect and disease pests such as elongate hemlock scale, hemlock looper, spruce spider mite, hemlock borer, root rot and needlerust accelerate the rate and extent of hemlock mortality.
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