Elongate Hemlock Scale
Pest: Fiorinia externa (Ferris)
Elongate hemlock scale (EHS) is primarily found infesting eastern hemlock (Tsuga canadensis) and Carolina hemlock (Tsuga caroliniana), along with fir and spruce in Massachusetts. It may also be found in cedar, Douglas fir, pine, and yew when those plants are grown nearby an infested hemlock. Elongate hemlock scale is an armored scale, non-native to the United States and first observed in New York in 1908. This invasive insect from Asia (native to Japan and China) has since moved throughout the state of Massachusetts and parts of the coastal Northeast in landscaped as well as forested areas.
Adult female 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 be thread-like in appearance. 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 mouth parts. 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.
EHS 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 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 or when populations are high.
Chemical management options can include foliar applications of horticultural oils, if complete coverage of the insect can be achieved (on smaller plants). These applications are usually more effective if made while crawler stages are present and exposed (not covered and protected by the waxy scale). Multiple applications per growing season may be required for management of this insect. A dormant oil application may be made between the end of March and early-April. A second application of horticultural oil according to label rates may then be made between late-May and early-June. Follow label instructions to reduce the risk of phytotoxicity when making any applications. Insecticidal soaps may be used, but since they dry quickly, it is difficult to time applications accurately so that they will impact the scale when it is in the vulnerable crawler stage.
On larger landscape specimens where complete coverage from foliar applications is difficult to achieve, systemic insecticides are available for management. Home owners will need to hire a licensed pesticide applicator to apply these materials. The systemic insecticide, dinotefuran, a neonicotinoid, 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. Although neonicotinoids are currently under review, particularly in reference to their potential impacts on pollinators, hemlock is primarily wind pollinated. For this reason, there is a reduced risk to bees and other pollinators, since there may be little to no pollen or nectar that would be attractive to beneficial insects (in some cases, pollen and nectar have been found to contain traces of systemic insecticides). Please note that another neonicotinoid, imidacloprid, does not manage elongate hemlock scale populations, but is effective against hemlock woolly adelgid.
As with all chemical insecticides, use best management practices to reduce drift, avoid applications during times of day when pollinators are most active or when flowers are in bloom, reduce impacts to non-target organisms, and observe all regulations when applying near schools, wetlands, and other sensitive areas or populations.
Management of elongate hemlock scale can be difficult to achieve, as all life stages of this armored scale insect can be present throughout the growing season, many of which are protected by the hardened scale covering. Multiple chemical applications are often necessary to keep populations down. Follow-up monitoring after chemical treatments should include using a hand lens or microscope to view the scales to determine whether live insects are present. Fertilizing trees with elongate hemlock scale, particularly with nitrogen-based fertilizers is discouraged. The added nitrogen may lead to population increases of the scale.
In some cases, highly infested landscape trees may be removed and disposed of away from healthy host plants. This option may be desirable for those who do not wish to make multiple chemical applications to manage this insect.