Over 95% of Christmas trees grown in North Carolina are Fraser fir, considered the premiere Christmas tree for its pleasant aroma, needle retention, and sturdy branches. (Photo by Robert Jetton, Ph.D.)

By Kelly Oten, Ph.D. and Robert Jetton, Ph.D.

Robert Jetton, Ph.D.

Kelly Oten, Ph.D.

When it comes to Christmas, most of us think about festive decorations, buying the perfect gift for that special someone, and playing Mariah Carey’s “All I Want for Christmas is You” on repeat. But for one tiny insect, the tune of the season might be “I’ll Be Home for Christmas”—because that’s exactly what it could be doing.

Meet the elongate hemlock scale (Fiorinia externa). Native to Japan and first described on hemlock trees (hence the common name), elongate hemlock scale attacks a wide range of conifers, including firs. That’s a big deal in North Carolina, where 4–6 million Christmas trees are harvested each year, contributing an estimated $375 million in direct value to the state’s economy annually. More than 95% of those trees are Fraser fir (Abies fraseri), nicknamed the “Cadillac of Christmas trees.” With sturdy branches for those heavy ornaments (calm down, Hallmark), excellent needle retention, and that unmistakable fir fragrance, it’s easy to see why it’s the top choice when it comes to Christmas trees.

These small, amber-colored spots on the underside of fir needles are elongate hemlock scale (Fiorinia externa)—an invasive and persistent insect that can persist on trees up to 13 weeks post-harvest. (Photo by Robert Jetton, Ph.D.)

But even the Cadillac has its maintenance issues. Fraser fir has its fair share of pests, but elongate hemlock scale (EHS) is one of the most challenging. Not only does it require a robust integrated pest management program to keep it in check, but it’s also a post-harvest pest, meaning it can cause trouble long after the tree is cut. As these trees are transported from mountain farms to tree lots across the country, EHS may be along for the ride, creating risk of introduction to new areas where it may pose new threats.

Choosing a tree is all part of the holiday magic—but what if that tree is hosting a few uninvited guests? (Photo by Kelly Oten, Ph.D.)

Until now, though, that risk was mostly speculative. How long could these insects actually survive once the tree was cut? Could they really make the trip from hillside to hearthside? How long would crawlers—the mobile first instar—emerge from eggs on the tree? That’s what we set out to test in a study at North Carolina State University, published in July in the Journal of Economic Entomology.

First, we evaluated EHS crawler emergence from baled and unbaled Fraser fir for 7 weeks. Interestingly, baled trees had fewer emerging crawlers than unbaled ones, likely because the tight wrapping restricted airflow and therefore crawler movement. That’s good news for shippers—but once trees are unbaled for display at retail lots or loaded onto open car roofs, all bets are off.

Second, we mimicked a 13-week rotation of a Christmas tree’s real-world journey—from outdoor tree lot to indoor living room to curbside discard. Unfortunately, live EHS was found throughout the process. When moving trees indoors, there was a noticeable surge in the number of crawlers, live females, and eggs, likely a result of the warmer temperatures and the tree receiving water. But EHS didn’t stop there. While EHS numbers declined as the trees desiccated, crawlers kept emerging for up to 13 weeks post-harvest, and live, egg-producing females were still present for up to 11 weeks post-harvest.

So yes—by the time you’re cursing the strings of lights that always get tangled, these tiny scales might still be clinging to your tree, producing offspring. Thankfully, EHS isn’t a threat inside your home, but for Christmas tree producers and inspectors, it’s a regulatory headache that demands close attention. While there’s no confirmed evidence (yet) that EHS has established new populations through Christmas tree movement, it’s a risk the industry—and regulators—take seriously. Our study underscores the importance of managing this pest in the field to reduce this risk. And, while it may not be the outcome we wished for, every study brings us closer to effective solutions. EHS might be persistent, but just like Rudolph, Hermey, and Yukon Cornelius, so are the people working on it.

Kelly Oten, Ph.D., is an assistant professor and extension specialist and Robert Jetton, Ph.D., is an associate professor in the Department of Forestry and Environmental Resources at North Carolina State University. Email: [email protected], [email protected].