The elongate hemlock scale, Fiorinia externa, is an armored scale that is a pest of eastern and Carolina hemlock in the Eastern United States. Elongate hemlock scale is believed to be native to Japan and accidently introduced into the United States. This scale pierces the underside of the needle with its mouthparts and removes the fluids from the needle. Trees that are severely infested will exhibit needle yellowing/dropping, thinning canopy, and eventual death.
Management may be difficult with contact insecticides for this pest since the life stages overlap throughout the growing season. There are many crawlers from May through June. Elongate hemlock scale outbreaks may increase after a tree has been infested with hemlock woolly adelgid, drought, or other stresses
Transtect systemic bark sprays or soil applications will be effective in controlling this scale. Severe infestations may require consecutive years of treatment before trees begin to fully recover.
Transtect infusible can be used as a tree injection treatment when other systemic applications or sprays are not feasible.
Maintaining healthy trees with supplemental watering during drought can decrease susceptibility. Fertilization with nitrogen can increase populations of this armored scale.
Other Treatment Practices
- Promote health and vigor with proper irrigation, mulching, proper pruning and prescription based fertilization practices.
- Adequate water is a key factor in maintaining stress free plants. A slow, deep watering event once every few weeks during dry conditions will help maintain soil moisture levels and minimize stress.
- Mulch is very beneficial for all trees because it reduces competition with turf and moderates soil temperature and moisture levels. The addition of 3 inches of wood chips or shredded bark under the drip line can have a very beneficial effect by holding in moisture and promoting healthy fibrous roots.
- Cambistat can be also be used to promote tree health and reduce the incidence and severity of stress mediated diseases and insect problems on trees growing in urban areas. •Do not use nitrogen fertilization, as nitrogen can increase populations of this elongate hemlock scale.
Transtect has performed well as a soil application in trials. Severe infestations may require consecutive years of treatment before trees begin to fully recover.
Signs of Damage
- A yellowish brown, flat, elongated, shell-like waxy covering about 1.5 mm long
- Waxy secretions on the lower surface of infested needles may be found
- Yellow foliage that drops prematurely giving a thin appearance to the crown
- Yellow banding may occur on the upper surface of infested needles
- Dieback of major limbs that starts at the bottom of the tree and progresses upward
- Death of entire tree within 10 years of heavy infestation
Trees At Risk
The principal host plants include:
- Eastern hemlock (Tsuga Canadensis)
- Carolina hemlock (Tsuga caroliniana)
Other species affected are:
- Northern Japanese hemlock (Tsuga diversifolia)
- Fir (Abies spp.)
- Spruce (Picea spp)
- Females deposit eggs under their waxy coverings and continue to do so through early summer.
- Eggs hatch in 3-4 weeks(1stGen 360-700GDD, 2ndGen 2515-2625GDD).
- Newly hatched crawlers move to new growth and feed on the underside of the needles for 3-4 weeks.
- Life stages overlap, so crawlers can be found throughout the spring and summer.
- Overwinters as an egg or adult female.
- One to two generations per year.
U.S. Forest Service
University of Maryland
A Treatment Guide is designed to help you identify a pest issue and management solutions. Always refer to product label for all rates and approved uses. Some images courtesy of forestryimages.org or Wikimedia Commons. Use of the images does not imply endorsement of treatments by forestryimages.org