Adelgids

Flip a hemlock twig. White tufts sit on the wood at the needle bases, like the tip of a cotton swab. That is an adelgid, not a walking houseplant pest and not a bump on a rose stem.

Adelgids are tiny, dark, aphid-like insects that feed only on conifers. They hide under waxy wool or inside a spruce gall. Most years a healthy spruce or pine lives with a few. Hemlock wool and fir-bark wool are the jobs that can kill.

• Smear the wool. A dark oval underneath confirms it.
• Clip green pineapple galls on spruce before they open.
• A spray that never wets the undersides will not finish this.

Flip the branch: cotton-swab tufts sit on the twig

Adelgids hide under white wool stuck to the twig at the needle bases, not painted onto the needle. Flip the newest growth. The tufts are separate and round. Smear one. A tiny dark oval sits under the wax. The wax is waxy, not stretchy silk.

The wool is easiest to see from late fall through early spring. In summer the insect may be a crawler with only a thin white fringe. On fir, look at the bark, not only the needles. On spruce, look for a pineapple-shaped swelling on new wood.

That wool is not aphids, scale, or mealybugs

Aphids have two little tubes on the rear and cluster on soft tips. Adelgids do not. They stay on conifers. If the cotton is in a houseplant leaf joint and it walks when you poke it, that is not this insect — see mealybugs.

Elongate hemlock scale paints tangled white onto the needle itself. Adelgid tufts sit on the twig. The two can share a hemlock. Do not run a scale crawler calendar here; see scale insects for that bump. Spider egg sacs pull apart. Pine sap is sticky and smooth. Stipple without wool is a mite leftover — see spider mites.

Woolly aphids on a deciduous shrub are a different leftover. See aphids rather than oiling a hemlock for that job.

Pineapple galls on spruce are still adelgids

Feeding on new spruce wood can swell the shoot into a pineapple-shaped gall. Eastern spruce galls sit at the base of this year’s growth, about a half inch to an inch. Cooley galls run longer, often one to three inches, on the tips, especially on blue spruce.

Douglas-fir is the other host for Cooley adelgid. Needles yellow and bend. Wool shows. Galls do not. The insect can finish a year on spruce alone, but injury is worse when Douglas-fir stands next to the spruce. Empty brown galls can hang for years after the insects have left.

Hemlock wool can kill; a spruce gall usually does not

Most adelgids on a vigorous spruce or pine are an eyesore. Tolerate a light gall year. A landscape hemlock with cotton on the newest twigs is a different job. Heavy hemlock woolly adelgid can drop needles, thin the crown, and kill the tree in about four years if nothing changes.

Balsam woolly adelgid lives on true fir bark. Nodes swell. Crowns thin. A heavy stem infestation can finish a fir in two to three years. Pine bark adelgid that snows a white pine trunk rarely kills the tree. Wait on felling a hemlock that you can still treat; cutting it will not stop the insect in the neighborhood.

Skip the nitrogen jolt

Quick-release fertilizer pushes soft growth adelgids like. Research on hemlock shows extra nitrogen can raise their numbers. Water a drought-stressed tree. Do not feed it as a recovery plan.

A new hemlock from the nursery can already carry crawlers. Keep it off the hedge for a week and look at the twig undersides before it shares a bed with a clean tree.

Clip green galls before they brown and open

On a small spruce you can reach, pick or clip galls while they are still green, usually before mid-July. That traps the insects inside. Bag the pieces. Brown, split galls have already let them out. Cutting those is leftover cosmetics. It does not rewind the year.

Eastern galls sit at the shoot base, so you lose the whole twig when you cut. Cooley tip galls come off with less of the branch. On a forest spruce, skip the ladder. The tree can carry a few galls.

Oil only if you can wet every underside

Horticultural oil or insecticidal soap smothers adelgids it actually touches. Drench the foliage, including the undersides, almost to runoff. A mist from the driveway does not. On a hemlock you can reach, two windows matter: after egg hatch in late winter to early spring, and again in early fall before new wool builds. Labels differ. Follow the one in your hand.

There is no leftover film once it dries. You will likely need another pass the next year. Oil can strip the blue bloom from blue spruce. The tree is still healthy. Broad leftover sprays that kill mite predators can leave you with spider mites a month later. Skip the brand aisle if coverage is the missing step.

Fail if one fog on a hot afternoon is the plan and the wool still sits dry on the twig.

A tall tree shrugs a garden hose

A forceful hose knocks cotton off bark and low limbs you can see. It does not finish a 40-foot hemlock. Handheld oil is honest on a hedge or a tree about ten feet. Taller than that, you are wetting the skirt and leaving the crown. Hire someone with real pressure or accept that you cannot finish it from the ground.

Do not clip an infested hemlock tip and mail it. Crawlers ride branches. Photograph the tufts on the twig and ask locally. Wait on a labelled systemic leftover until an arborist has looked at a specimen you mean to keep. Skip that aisle as the whole plan.

Confirm the tree, then hose, clip, or oil

1. Confirm the wool. Tufts on the twig at needle bases. Smear it. A dark oval is adelgid.
2. Name the tree. Hemlock and fir bark wool can kill. Spruce galls and pine-bark snow usually wait.
3. Clip green galls on spruce you can reach, before they brown and open. Bag them.
4. Hose cotton on trunks and low limbs. Empty the debris. Skip nitrogen.
5. Oil or soap only if you can wet every underside. Repeat the next year. Fail if the finish is a bottle on a tree you cannot reach.

Related reading

• Aphids — tubes on the rear, soft tips, not conifer wool on the twig.
• Scale insects — bumps and painted needle film, including elongate hemlock scale.
• Mealybugs — walking cotton in leaf joints, not a hemlock swab.
• Spider mites — stipple and silk; leftover after a harsh spray that killed their predators.