Adelgids & woolly aphids
Adelgidae & Eriosoma lanigerum
also called Hemlock woolly adelgid, Woolly apple aphid
White woolly tufts along twigs and at the base of needles, each hiding a sap-sucker. On hemlock the woolly adelgid is a killer; on apple it is mostly disfiguring.
How to know it
You see the wool, not the insect: dense white cottony masses at the base of hemlock needles, along spruce twigs, in the crotches of apple branches, or as a fluffy coating on a pruning scar. Rub the wool away and there is a small purple-gray soft-bodied insect beneath. On spruce the feeding produces cone-shaped galls at the shoot tips.
What you'll see
- White woolly blobs at the base of hemlock needles on the underside of the twig, obvious in winter.
- Cottony fluff in the branch crotches, at pruning wounds and around cankers on apple.
- Needles graying and dropping, branch tips dying, and a hemlock thinning from the bottom up.
- Pineapple-shaped galls at the ends of spruce shoots, green then brown and woody.
- Sticky honeydew below the infestation, with sooty mold settling on it.
Where it comes from
Adelgids reproduce without mating and go through several generations a year, some species alternating between spruce and larch or pine. The hemlock woolly adelgid feeds through winter — unusually — and has two generations a year, which is part of why it is so destructive. Woolly apple aphid overwinters on the roots and on cankers and moves up the trunk in spring.
Hemlock woolly adelgid is established through the eastern hemlock range and is limited mainly by very cold winters, which are becoming less reliable. Woolly apple aphid favors stressed, over-pruned apples with plenty of wounds and water shoots.
Dealing with it
- Scrub woolly apple aphid off the bark with a stiff brush and soapy water, and cut out the water shoots and cankers it colonizes.
- Spray a small hemlock thoroughly with horticultural oil or insecticidal soap in spring and again in autumn, wetting the needle undersides completely.
- Have a valued large hemlock treated by an arborist with a soil-applied systemic; it is the only measure that reliably saves a big tree.
- Water and mulch hemlocks in drought, since a stressed tree dies far faster.
- Do not shear or fertilize an infested hemlock, which pushes exactly the soft growth the adelgid wants.
Keeping it out
- Inspect nursery hemlocks and spruces for wool before buying, and quarantine them.
- Do not move hemlock branches or Christmas greens out of an infested area.
- Prune apples cleanly and avoid leaving stubs and torn wounds, which are the colonization points.
- Grow woolly-aphid-resistant apple rootstocks — the MM series was bred for exactly this.
- Encourage the predatory beetles and lacewings, and consider the released Laricobius beetles where a biocontrol program is running.
What it goes for
Hemlock, spruce, larch and pine among the conifers; apple, cotoneaster and pyracantha for the woolly aphid.
Trouble it brings with it
Who hunts it for you
- Green lacewingChrysoperla carnea Its bristly larvae — "aphid lions" — impale aphids, mealybugs, thrips, and mite colonies, eating hundreds a week. Adults feed on nectar and pollen from small open flowers and overwinter in hollow stems left standing. Grow to recruit it: Cilantro,Cosmos,Dill,Sunflower,Yarrow
- Ladybird (lady beetle)Coccinellidae The gardener’s favorite ally: adults and their alligator-shaped larvae each eat thousands of aphids, plus scale, mealybugs, and other soft-bodied sap-suckers. Grow flat, open flowers for the adults and never spray a colony that ladybird larvae are already working. Grow to recruit it: Calendula,Cilantro,Cosmos,Dill,Fennel,Yarrow
See also
The Cottage Garden Companion — the gardener's bestiary at cottagegardencompanion.com