Tree problems · Insect
Hemlock woolly adelgid: signs and what to do
Hemlock woolly adelgid is an insect pest, often seen on eastern hemlock, Carolina hemlock. Look for: small white, cottony tufts at the base of needles on the underside of twigs.
General information, not a diagnosis. A certified arborist or your county extension office can confirm.
- Insect
- Eastern hemlock
- Carolina hemlock
Signs to look for
Tick what you see. More ticks make it more likely, but only an on-site look can confirm.
0 of 6 signs ticked. Ticks stay in this browser only.
Season
The white tufts are visible on twigs for much of the year and are often easiest to spot in late winter and spring. The tree usually declines slowly over several years.
How it spreads
The insect is tiny and spreads on wind, birds, deer and people. Moving infested nursery stock is a common way it reaches new places.
Where it is found
Hemlock woolly adelgid is an invasive insect from Asia that has been found in many parts of the eastern United States and in parts of the Pacific Northwest. Check your state official map; ranges change.
Official sources
What to do
- 1
Look closely at the underside of twigs near the needle base for white cottony tufts.
- 2
Call a certified arborist to confirm. Other things, like pollen or spider webs, can look similar.
- 3
Ask about systemic insecticides applied to the soil or injected into the trunk. Forest Service guidance says these can work on large trees.
- 4
Plan to repeat treatments as the arborist advises, because one treatment does not protect a tree forever.
- 5
Report the find to your state forestry or agriculture office if the pest is new to your area.
Safety first: do not climb, do not cut near power lines and do not use a chainsaw on storm-loaded wood. Call the utility for downed lines and 911 if anyone is in danger.
Prevention
Keep hemlocks watered in dry spells, because stressed trees decline faster. Buy hemlock nursery stock only from a source you trust and inspect it. Do not move hemlock branches or firewood with needles. Avoid heavy nitrogen fertilizer on infested hemlocks; extension guidance generally advises against it.
When to call a pro
Call an arborist when you see white tufts on twigs, when hemlocks start thinning, or before spending money on any treatment. Early treatment gives the best chance to save a tree.
Not sure who to call? Read how to hire a tree service or check is my tree dangerous?
Trees it affects
Usually seen on: Eastern hemlock, Carolina hemlock.
See all species in our tree library, or pick a tougher tree with the tree picker.
For tree companies
How to explain hemlock woolly adelgid to a customer
Tell the owner that this pest can kill a hemlock slowly, and that treatment is a repeating job, not a one-time fix. Give a written plan with the treatment type, how often to repeat and what you cannot promise. If the tree is already mostly dead, say so plainly and talk about safe removal.
Send this page to the customer after your visit so they can read the signs in plain words. See also selling plant health care and the job photo checklist.
Questions
How can I tell if my hemlock has woolly adelgid?
Look at the underside of the twigs at the base of the needles. Small white cottony tufts, like tiny cotton balls, are the main sign. An arborist can confirm.
Can a hemlock be saved?
Often yes, if it is caught while there is still plenty of live foliage. Systemic insecticides are the main tool for large trees. A badly thinned tree has a lower chance.
Do I need to treat every year?
Not always. The right schedule depends on the product, the tree and your area. Ask a certified arborist for a plan in writing.
Is the insect dangerous to people or pets?
No. The risk is to the hemlock. A dead hemlock can fall, so remove dead trees near a house or road.
Can I just spray it with a hose or soap?
For a small shrub-size hemlock, some extension guidance mentions horticultural oils or soaps. For a tall tree, spraying is hard to do well. Ask an arborist.
What if I think the pest is new to my area?
Contact your state department of agriculture, state forestry office or county extension office. They track new finds and can tell you what to do.
Can Lirevon diagnose hemlock woolly adelgid on my tree?
No. Lirevon is a remote marketing team for tree service companies and does not do tree work. This page is general information, not a diagnosis. A certified arborist or your county extension office can confirm what is wrong with your tree.
How do I find a good local pro for this?
Search Google Maps for certified arborists or tree services near you, read their reviews and ask for proof of insurance. Get two or three written quotes. Our guide on how to hire a tree service lists the questions to ask.
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