Landscape - Elongate Hemlock Scale

The following is information on the Elongate Hemlock Scale, a difficult to control pest in this area.

ELONGATE HEMLOCK SCALE.

In our area, no scale insect is more frustrating than elongate hemlock scale (EHS). A major threat to conifers, damage from scale feeding causes eventual needle drop and branch dieback. There is no honeydew produced.

Breaking all the rules this scale has no set generational times in our climate and overwinters in the egg, nymph, or adult stage. Development progresses with warm weather in the early spring. Brown, 1.0 mm long oval shells house the females; males are slightly shorter, white and oystershell-shaped. Eggs hatch within the female shell cover and crawl out through a one-way flap at its rear. The orange crawlers quickly settle, molt, and develop into males or females. Adult females are completely protected within their hard shell; only their mouthparts protrude through its bottom to feed. These shells remain on the plant after the females have died, so scouting to ensure that infestations are active is very important.

Biological control does not provide meaningful suppression of EHS. The use of growing degree days or plant phenologies to predict crawler emergence patterns is futile. Several different researchers investigated EHS management, and have come up with variable results. Studies in Central PA favored spring applications of Tristar (acetamprid), a foliar-applied neonicotinoid. Safari (dinotefuran) drenches showed promise in studies by the Univ. of CT and would appear to be the most mobile neonicotinoid compound best suited for armored scale control. The Univ. of MD saw suppression of EHS using spring applications of horticultural oil, Merit (imidacloprid) soil drenches, and Distance (pyriproxifen). Remember that some neonicotinoid applications may lead to mite outbreaks. Our work at Longwood had great results with October applications of 2% v:v horticultural oil, while Merit soil drenches and Distance sprays were ineffective.

Information from Casey Sclar, IPM Coordinator, Longwood Gardens