Adult female elongate hemlock scales (EHS) are covered with an orange-brown waxy coating (test) that is approximately 1/20th of an inch long and longer than it is wide. The adult female and her eggs are yellowish-orange in color, as is the crawler or mobile stage. The immature males are slightly smaller and coated with a whitened-waxy test, which can sometimes appear to be covered in threads of white wax. Adult males are tiny, winged, and mobile and fly to the stationary adult females to mate.
Multiple life stages may be present throughout the growing season. Egg hatch generally occurs by the end of May or beginning of June, leading to the movement of crawlers from underneath the female’s test (waxy covering), which settle at the underside of host plant needles, where they feed using their piercing-sucking mouthparts. Males and females mature, and the winged males then seek out matured females to mate. These mated females produce further eggs beneath their hardened coverings, and many life stages may overwinter. However, this insect primarily overwinters as eggs or fertilized females. These overlapping life stages can make management difficult. In the Northeast, one generation per year has been observed, whereas warmer areas in the southeastern United States may experience two generations per year.
Elongate hemlock scale damages the host by inserting its piercing-sucking mouthparts into the needle tissue and sucking out the fluids of the plant. This can cause chlorosis (yellow spotting) of the needles, premature needle loss, branch and limb dieback, and may also contribute to the eventual death of the tree, especially in the presence of other pests, stressors, or when populations are high. Even mature hemlock may be killed.
When scouting host plants, search for infestations of this insect in the lower branches first, then move upward. Look for hosts with a yellowed appearance. Damage to lower branches may at first appear to be related to spider mite activity. Look for the presence of the life stages of elongate hemlock scale to differentiate between the two.
Prune out heavily infested branches and destroy. Avoid allowing this insect to establish in Christmas tree plantations where fir is present. Avoid using nitrogen fertilizers on trees infested with elongate hemlock scale, as this action has been found to increase the population of this insect.
There are several parasites and predators of the elongate hemlock scale, but they are said to provide limited control in managed landscapes.
Several natural enemies of hemlock scales are present under natural conditions. A parasitoid wasp, Encarsia citrina, regularly kills approximately 90% of the elongate hemlock scale population in Japan and is considered to be well established in the United States (Abell and Van Driesche, 2011). The predatory beetle, Cybocephalus nipponicus, also attacks the elongate hemlock scale. In addition, lady beetles and lacewings are commonly found on coniferous trees and are considered to be generalist predators of scale insects. Entomopathogenic fungi, such as Colletotrichum fioriniae (Marcelino et al., 2008) and Conoideocrella luteorostrata (Hywel-Jones 1993), have also been found to impact elongate hemlock scale populations.
Abamectin (NL)
Acephate (NL)
Acetamiprid (L)
Azadirachtin (NL)
Buprofezin (NL)
Carbaryl (L)
Chlorpyrifos (N)
Clothianidin (NL)
Cyantraniliprole (NL)
Cyfluthrin (NL)
Dinotefuran (NL)
Gamma-cyhalothrin (L)
Horticultural oil (L)
Insecticidal soap (NL)
Lambda-cyhalothrin (L)
Neem oil (NL)
Pyrethrin+sulfur (NL)
Pyriproxyfen (eggs) (L)
Spinetoram+sulfoxaflor (N)
Host plants should be treated while this species is in the crawler stage of development if using contact insecticides. All life stages can be present throughout the growing season, and therefore it is difficult to target the crawler stage.
Active ingredients that may be applied systemically include: abamectin (injection), acephate (injection), acetamiprid (injection), azadirachtin (injection, soil drench), clothianidin (soil drench), cyantraniliprole (soil drench, soil injection), dinotefuran (soil drench), and neem oil (soil drench).
When used in nurseries, chlorpyrifos is for quarantine use only.
The systemic insecticide, dinotefuran (neonicotinoid; state restricted use), can be effective within weeks of application. Application can be done as a trunk injection, soil drench, or basal bark spray. Bark sprays for elongate hemlock scale have been reviewed with success, although yearly applications may be necessary to achieve management of this insect. Dinotefuran can also protect trees from hemlock woolly adelgid for about 2 years. Imidacloprid is not effective against managing the elongate hemlock scale.
Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.
Note: Beginning July 1, 2022 neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.
