Diseases, pests, hitchhikers and other bad holiday guests

The guardians at DATCP work to keep them out of your Christmas trees

A Wisconsin tree farm. Photo courtesy of DATCP.
Working on a Wisconsin tree farm. Photo courtesy of DATCP.

Here are a few things you don’t want to think about this Christmas as you look across the room at your beautiful, live Christmas tree: root rot, elongate hemlock scale infestations, needle blight, cankers, gypsy moth eggs or other hitchhiker pests.

DATCP inspectors check out branches during an inspection at a Wisconsin Christmas tree farm. Photo courtesy of DATCP.
DATCP and USDA-APHIS staff members examine a Fraser fir branch during an inspection at a Wisconsin Christmas tree farm. Photo courtesy of DATCP.

Wisconsin is one of the top five Christmas tree producing states in the nation, so keeping all those trees pest-free is no small job. 

Thanks to vigilant Wisconsin tree farmers and the plant protectors at the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) led by Plant Industry Bureau Director Brian Kuhn, you can go back to sipping your brandy-spiked eggnog. His team at DATCP licenses Christmas tree growers — managing and monitoring for pests and diseases, acting as a resource for growers and issuing certificates for in-state, interstate and international shipment of plants.

An example of Elongate Hemlock Scale (EHS) pests close up. Photo courtesy of WI DATCP
Elongate Hemlock Scale pests close up.

Last year one unwanted holiday guest that came to Wisconsin was bad enough to require public warnings — a tiny insect known as elongate hemlock scale, which is not in Wisconsin forests or evergreen fields. The bugs, which feed on the underside of conifer needles, showed up in some chain stores that buy trees and wreaths in bulk elsewhere, including Menards and Home Depot. They were found in Fraser and balsam fir boughs and wreaths coming from Pennsylvania, North Carolina and Virginia.

Little bugs or larvae are not as visible as other unwanted guests found thus far this 2019 holiday season such as an owl that a child in Georgia thought was a scary ornament that caused her to burst into tears when it moved, or the 10-foot python adorning a tree in Australia. 

But Wisconsin keeps the unwanted invasive out and has to keep its own invasive infestations to ourselves — in particular the maligned gypsy moth. 

Headshot of DATCP Bureau of Plant Industry Director Brian Kuhn (provided by DATCP)
DATCP Bureau of Plant Industry Director Brian Kuhn (provided by DATCP)

Kuhn said approximately two-thirds of the state falls into the gypsy moth quarantine area and his department must issue certificates that exported Wisconsin trees are clear of the moths. That’s caused his department’s workload to rise as the quarantine area has expanded.

“It’s definitely caused that Christmas tree inspection effort in the fall to be a much larger effort than it historically was,” says Kuhn. “That workload that allows us to ship trees will climb over time … because of the competing efforts of the hemp program I couldn’t pull those inspectors in this year. But we got all our inspections done.”

Moving trees

While Christmas trees are grown all over Wisconsin and there are many hundreds of fields with some in every county, there are hotbeds such as Wautoma and Eau Claire, areas where all the DATCP inspectors go and do a mass inspection.

An example of Elongate Hemlock Scale (EHS) pests. Photo courtesy of WI DATCP
An example of Elongate Hemlock Scale (EHS) pests. Photo courtesy of WI DATCP

According to the latest Wisconsin agriculture census in 2017, more than 700,000 trees were cut from 859 Christmas tree farms. The value of those trees totaled more than $18 million.

Christmas trees are further proof of the “buy local is best” saying — that means less worry that pests are being transported in or out of quarantine districts or states.

“The movement of Christmas trees really is interesting because it’s kind of like firewood, they move in all directions all the time,” says Kuhn, whose job can often require tracking down exactly where infected trees might be heading. “We produce enough Christmas trees here to feed Wisconsin just fine on Christmas trees, but we need to develop grower relationships with different markets. We’ve got trees going out West. We’ve got trees going to Florida, Missouri, you know, all over the country.” 

When the pests are spotted on a wreath in a store, for example, it triggers a chain of quick reactions.

A Wisconsin tree farm. Photo courtesy of DATCP.
Working on a Wisconsin tree farm. Photo courtesy of WI DATCP.

“I’m talking to my counterpart in Illinois and my counterpart in Minnesota, and we’re comparing notes on what they’re seeing in their stores,” Kuhn says. “So when I call and talk to that live plant buyer for one of those big box stores, they know it’s not just in Wisconsin that there’s an issue… We’ve had a lot of really good cooperation there. We’ve been doing a lot of education and outreach to those kind of folks so that we don’t relive this again, year after year.”

DATCP inspectors check out branches during an inspection at a Wisconsin Christmas tree farm. Photo courtesy of DATCP.
A DATCP inspector examines a seriously sick fir tree during an inspection at a Wisconsin Christmas tree farm. Photo courtesy of DATCP.


If there’s ever a mystery bug, Kuhn uses the Bat Phone to ring UW-Extension entomologist PJ Liesch in the UW-Madison Insect Diagnostic Lab. Other times his counterparts at the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service will step in to help with inspections or information. Kuhn refers to these relationships as his “continuum of plant protection folks that all work together as a team.”

In the field, the inspectors seek out physical evidence, such as a buff-colored egg mass that might be on the trunk of the Christmas tree. They also survey field edges where oak trees are a good indicator of potential gypsy moth problems. 

“They’re looking for evidence — yellowing of the needles, dieback on branches. And once they see that evidence, they can key in and dig a little deeper. Then they find the exit hole. They know what that’s characteristic of, they’re cutting into those cankers that they’ll find on a tree and they’ll pull out a larvae of a certain pest that they know and can identify what that is.” And if they can’t ID it, they may even reach out as far as the Smithsonian Institute to discover what kind of pest it is.

Wisconsin Capitol holiday Christmas tree 2019 (photo by Melanie Conklin)

Kuhn and his inspectors may not know it, but they share something in common with Taylor Swift, whose new hit “Christmas Tree Farm,” is based around her memories of her dad’s Christmas tree farm where her childhood job around the holidays was plucking praying mantis pods off of Christmas trees so buyers didn’t get holiday insects.

Kuhn says there are not praying mantis pods on homegrown Wisconsin trees. But for more on spider mites, needle necrosis, cankers, yellow-green mottle syndrome, twig weevils, needle midges, blight and other diseases and infestations that can strike Christmas trees, a USDA grant funded this color brochure with plenty of descriptions and photos. Just bring it out to stop family members who launch into politics or other undesirable holiday table talk.

But on the inside, rest assured with this knowledge: Brian Kuhn himself keeps live evergreens in his house for the holidays.

Extra: Get real!

The Wisconsin Christmas Tree Producers Association, headquartered in Portage, provides a list of reasons to buy real trees: 

  • Tree farms stabilize soil, protect water supplies and provide refuge for wildlife while creating scenic green belts.
  • Often, Christmas trees are grown on soils that could not support other crops.
  • Real Christmas trees absorb carbon dioxide and other gases, emitting fresh oxygen to benefit the atmosphere. This helps prevent the earth-warming greenhouse effect.
  • For every real Christmas tree harvested, two to three seedlings are planted.
  • Real Christmas trees are an all-American, recyclable resource. Artificial trees, most of which are manufactured in Korea, Taiwan or Hong Kong, consist of plastics and metals that aren’t biodegradable. When disposed of, the artificial trees will never deteriorate.
Melanie Conklin
Melanie Conklin is proud to be a native of the state of Wisconsin, which gave humankind the typewriter, progressivism and deep-fried cheese curds. Her several decades in journalism include political beats and columns at Isthmus newspaper, the Wisconsin State Journal and other publications. When not an ink-stained wretch, she served time inside state, local and federal government in communications. She is excited to be back at the craft of journalism as Deputy Editor of the Wisconsin Examiner. It’s what she’s loved ever since getting her master’s degree in journalism from the UW-Madison. Her family includes one husband, two kids, four dogs and five (or more) chinchillas.