Protecting Hemlocks from Woolly Adelgid: Early Detection and Treatment

The Threat: Hemlock Woolly Adelgid

The hemlock woolly adelgid (Adelges tsugae) has devastated hemlock stands across the Appalachians. This tiny, aphid-like insect feeds at the base of needles, causing needle loss, branch dieback, and eventual tree death. Proactive monitoring is your best defense.

Monthly Inspection Routine

From late winter through early summer, examine the undersides of young needles on each hemlock. Look for white, cottony tufts—about the size of a pinhead—clinging to the twigs. These are the adelgid's protective wool coverings. Spring is the easiest time to spot them because new growth makes the white masses more visible.

When to Act

• No adelgids found: Continue monthly checks. No treatment needed.
• Adelgids detected on your trees: Apply a soil drench containing imidacloprid (a systemic insecticide) following label rates. The tree absorbs the chemical and kills feeding adelgids.
• Adelgids on nearby trees: Treat preventively with a soil drench or hire a certified arborist for trunk injection or other professional options.

Long-Term Vigilance

Even after treatment, keep monitoring. Reinfestation from surrounding areas is common. Healthy, unstressed hemlocks tolerate light infestations better, so water during droughts and avoid compacting soil over roots.