Elongate hemlock scale

What is elongate hemlock scale?

Elongate hemlock scale is an armored scale insect that was most likely brought in from Japan. It was first recorded in New York in 1908. Females live under a hard, brown, oblong cover on the underside of needles. Males have smaller white covers and become tiny winged adults.

The scales feed on cells inside the needles. Penn State says this causes yellow banding, early needle drop and a thin crown, and weakens trees so hemlock borer and Armillaria root rot can move in. UMass Extension says heavy populations, especially with other stresses, can help kill even mature hemlocks.

Because all life stages overlap through the season, the scale is hard to control with one well-timed spray. NC State says it feeds mostly on needle cells rather than only on sap, which makes it harder to control with systemic insecticides. Imidacloprid is not known to control it.

Signs and damage

• Yellow spots or bands on the upper side of needles
• Small brown, oblong scale covers on the underside of needles
• White waxy specks from male scales on needles in summer
• Early needle drop and a thin-looking crown
• Branch dieback

Elongate hemlock scale identification: what to look for

• Adult: Female: flat, elongate, light yellow-brown to orange cover about 1.5 mm (about 1/16 inch) long on the needle underside; body under it is yellowish-orange. Male: smaller white cover; adult male is a tiny winged insect.
• Eggs: Yellowish-orange, laid under the female's cover; about 20 per female.
• Larva: Crawlers are yellow and not elongated. They move to new needles on the same tree, then settle and never move again (females).
• Damage: Yellow spots or bands on needles, early needle drop, thin crown, branch dieback. Lower-branch damage can look like spider mite injury.
• Timing: In PA, crawlers are most plentiful late May through early June, but stages overlap all season.

Life cycle

Spends the winter mainly as eggs or mated females. Eggs hatch in about three to four weeks (Penn State); UMass says hatch is generally by the end of May or early June in the Northeast. Crawlers move to new needles, or are carried by wind or birds to other trees. Females settle and stay put under their covers, while males grow wings and fly to mate. Penn State says mated females lay a second batch of eggs six to eight weeks after mating. UMass reports one generation a year in the Northeast, and NC State reports two overlapping generations in the southern Appalachians, so all stages are often present at once.

When to look: Peak crawlers are late May to early June in Pennsylvania. Male wax is easiest to see in summer and early fall. Scales can be found on needle undersides all year.

Elongate hemlock scale look-alikes

A few things get mixed up with it:

• Hemlock woolly adelgid (Adelges tsugae): Penn State notes that heavy waxy strands can make needles look white and be mistaken for HWA. HWA sits at the base of needles under a white cottony ball. EHS has flat brown covers along the underside of the needle.
• Cryptomeria scale: NC State says it is the most damaging scale on Fraser fir in parts of North Carolina and Virginia. It also sits on the needle underside, but its scales are round rather than elongated.

How to control elongate hemlock scale

Cultural control

• Prune out and destroy heavily infested branches.
• Avoid nitrogen fertilizer on infested trees; research shows it boosts scale numbers.
• Keep trees healthy; Penn State says this may slow population growth.
• Avoid broad-spectrum sprays that kill the scale's natural enemies.

Biological control

• The tiny parasitic wasp Encarsia citrina is established in the US; an empty scale cover with an exit hole means it was parasitized.
• Lady beetles (including Chilocorus stigma), the predator beetle Cybocephalus nipponicus, lacewings and some fungi also feed on it, though UMass says they give only limited control in landscapes.

Chemical control

Penn State says to target crawlers with a registered insecticide in late May to early June, with a second application in early July if needed, and repeats as needed until mid-September. Horticultural oil is listed by UMass and NC State; NC State reports about 65 to 75% control. Among systemic active ingredients, NC State found dinotefuran and acetamiprid gave consistent control and buprofezin (an insect growth regulator) worked on immature scales; imidacloprid does not control EHS, and Penn State says soil-injected systemics used for HWA don't work on it. NC State warns that some pyrethroids can make scale worse by killing natural enemies. Use only products labeled for this use; the label is the law. Have an ISA Certified Arborist or licensed applicator treat large hemlocks. Muthler Landscaping does not treat trees or apply pesticides; see our pesticide applicator license guide.

Use only products labeled for this pest and this site; the label is the law. For trees, work with an ISA Certified Arborist. If you hire someone to apply pesticides, make sure they hold your state’s pesticide applicator license; the rules for each state are in our pesticide applicator license guide.

Prevention

• Inspect hemlock, fir and other conifer nursery stock for scale covers on needle undersides before planting.
• Check the receiving state's rules before shipping hemlock, fir or other conifers, including Christmas trees and wreaths, out of Pennsylvania.
• Scout lower branches of hemlocks each year.

When to call a pro

Call an ISA Certified Arborist if a valued hemlock has yellowing, thinning foliage, especially if it also has HWA. A pro can confirm which pest is present, since the treatments differ, and treat large trees.

Related guides: Tree database: mature size and planting distance · Pennsylvania tree identification · Firewood rules by state · All pests and diseases

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