Recent detection of scale species on fir trees in Michigan Christmas tree farms

Elongated hemlock scale and Cryptomeria scale have been found on fir Christmas trees in Michigan.

Fir needles with numerous small, yellow-brown scale insects (cryptomeria scale) scattered along the undersides, giving the needles a speckled appearance.
Crytpomeria scale in Fraser fir. Photo by Rayanne Lehman, Pennsylvania Department of Agriculture, Bugwood.org.

Scale insects are common but sometimes challenging pests to control in Christmas tree production. Growers of Scots pine are likely very familiar with damage caused by pine tortoise scale and pine needle scale. In Michigan, it has been rare to find scale insect pests infesting true firs. In other Christmas tree production regions, however, this is not the case. Elongate hemlock scale (Fiorinia externa) and Cryptomeria scale (Aspidiotus cryptomeriae) are major insect pests in other states including Pennsylvania, Virginia and North Carolina. These pests seem likely to become an increasingly important concern for Michigan growers with Fraser, balsam or Canaan fir trees.

Elongate hemlock scale was first found on hemlock trees in western lower Michigan in 2010. It was likely introduced into the state on infected hemlock nursery stock. Since then, elongate hemlock scale has spread and is present in many areas in Lower Peninsula counties bordering Lake Michigan. Although elongate hemlock scale is primarily a pest of hemlocks, often co-occurring on trees infested with hemlock woolly adelgid (Adelges tsugae), it can also colonize fir trees.

In 2025, Christmas tree growers in Ottawa and Kent counties found elongate hemlock scale on a few of their Fraser fir trees. As populations of elongate hemlock scale continue to build, the potential for spread into additional Christmas tree fields will increase.

The elongate hemlock scale feed on the underside of needles on hemlock and fir trees. Infestations of elongate hemlock scale are unlikely to kill trees but when densities are high, needles appear “dirty” due to the waxy covering on these armored scales. If enough needles are infested, trees can be unmarketable. Multiple years of infestation can lead to smaller needles, perhaps reducing growth (Photo 1).

Close-up of fir tree needles heavily infested with elongated hemlock scale, showing a grayish, waxy coating across the foliage.
Photo 1. Elongated hemlock scale on Fraser fir. Photo by Bill Lindberg, MSU Extension.

Controlling elongate hemlock scale is often challenging because life stages typically overlap, making it difficult to identify the optimal window for applying a cover spray. In addition, because elongate hemlock scale is invasive, other states have issued restrictions on Michigan Christmas and nursery trees to prevent spreading elongate hemlock scale into their states.

In Michigan, cryptomeria scale, also known as the “fried egg scale,” was first detected on hemlock trees in Berrien County located in southwest Michigan in 2022. Like elongate hemlock scale, cryptomeria scale is an armored scale and the waxy coating over the insects degrades trees appearance (Photo 2). Using a hand lens, you can easily identify the white translucent scale covering with a yellow female underneath (Photo 3), somewhat resembling a fried egg.

Fir needles with numerous small, yellow-brown scale insects (cryptomeria scale) scattered along the undersides, giving the needles a speckled appearance.
Photo 2. Crytpomeria scale in Fraser fir. Photo by Rayanne Lehman, Pennsylvania Department of Agriculture, Bugwood.org.
Extreme close-up of fir needles showing circular white and yellow scale insects (cryptomeria scale) attached to the needle surface.
Photo 3. Cryptomeria scale. Photo by United States National Collection of Scale Insects Photographs, USDA Agricultural Research Service, Bugwood.org.

What should growers do?

Michigan State University Extension recommends regularly scouting trees for signs of insect pests, including elongate hemlock scale and cryptomeria scale. Both insects can be readily observed on infested trees in late summer. While neither insect is common on fir Christmas trees currently, that could change in the future.

Growers should try to prevent non-native pests from establishing in Michigan.

Although birds or perhaps other wildlife could potentially move crawlers to a new tree, the tiny crawlers rarely travel very far. In fact, elongate hemlock scale and cryptomeria scale females are mobile only as “crawlers,” the first stage after hatching.

Alternatively, human activity is a leading contributor to the spread of these and other invasive insect pests. In a recent trial, live and active elongate hemlock scale crawlers were found on cut Christmas trees 90 days after harvest. If you are receiving pre-cut trees or other plant material from other Christmas tree regions where these pests are present, be vigilant to prevent introducing these insects to your farm.

 

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