Elongate Hemlock Scale

Elongate hemlock scale (Fiorinia externa), or EHS, is an invasive pest introduced into the U.S.​ from Asia. It feeds on a wide variety of conifers besides hemlock, including fir and spruce. It damages trees by feeding on the undersides of their needles, sapping nutrients from the trees and weakening them. This makes them susceptible to other pests and diseases. 

Where EHS Has Been Found

EHS has been detected in the District of Columbia, and the states of Connecticut, Delaware, Georgia, Kentucky, Maine, Maryland, Massachusetts, Michigan, New Hampshire, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Rhode Island, South Carolina, Tennessee, ​Vermont, Virginia, and West Virginia. 

EHS in Wisconsin

To date, EHS has not been found in Wisconsin’s forests or Christmas tree fields. However, Department of Agriculture, Trade and Consumer Protection inspectors have found it on cut Fraser and balsam fir Christmas trees and boughs, in wreaths and other evergreen decorations, and on hemlock nursery stock. All these items came from suppliers in states where it has already been established. In spring 2018, inspectors found infestations on hemlock nursery stock from Pennsylvania in two separate instances.  Later in the year, it was detected in wreaths, swags, boughs, and arrangements of evergreens in containers at several large chain stores. All had received their stock from four suppliers in North Carolina. Inspectors also intercepted infested boughs from Virginia at one outlet before they had entered the retail market.

The Risk in Wisconsin

Wisconsin is a major Christmas tree state. Christmas trees are an important product in-state and for export, and choose-and-cut farms are important to the agro-tourism industry. EHS feeds on eastern hemlock, as well as fir and spruce, which are among the most valuable Christmas trees. EHS produces 1-2 generations a year, and each generation feeds during multiple life stages, unlike many other insect pests. The insects wrap themselves in a hard, waxy coating, which creates the distinctive “scale” visible on needles. Because of these characteristics, EHS is difficult and expensive to treat with pesticides. 

In addition to the threat to Christmas tree fields, EHS also poses a risk to our native hemlock forests and other coniferous forests, as well as to ornamental evergreens in parks and yards.

Signs of EHS

  • Yellowing of needles on the interior of the lower branches; damage moves upward as population increases
  • Scale coverings on the underside of the needles
  • Premature needle drop; eventual branch and limb dieback and death of tree with severe infestations
  • Tree may appear flocked

Prevent EHS from Becoming Established in Wisconsin


If you bought evergreen wreaths, swags, bough, or arrangements at a chain store for the holidays, dispose of them at the end of the holiday season by burning or bagging them and putting them in your trash. Do not compost them or put them out for collection.

Businesses selling nursery stock and Christmas trees

  • Buy stock grown in Wisconsin or other states where EHS has not been found.
  • Let suppliers know that you will not accept stock infested with EHS or other pests.
  • Watch for any sign of EHS and report suspect EHS on trees to DATCP, using contact information on this page.
  • Dispose of known infested material by burning or landfilling.​

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