WESTMINSTER, Colorado – December 13, 2021 – Christmas trees are central to many a holiday celebration. But behind the scenes, it takes a multiyear effort to bring even a single tree to market, experts with the Weed Science Society of America (WSSA) say.
One example: A Fraser fir is typically eight to 12 years old before it is ready for harvest. “That means growers must make a long-term commitment to manage weeds across the many stages of a tree’s growth,” says Joseph C. Neal, Ph.D., a professor and extension specialist at North Carolina State University.
Why the emphasis on weed control? Weeds can reduce growth rates and tree quality in Christmas tree crops by competing for nutrients, water and light. They can create a fire hazard, influence needle color, and harbor insects and diseases that affect marketability. In addition, vines and tall woody-stemmed weeds and saplings can grow through trees and impede the annual sheering process necessary to promote a pleasing shape.
Experts say weed management starts at the seedling stage to ensure each tree gets off to a strong start. One example: Growing trays are sterilized with steam to prevent diseases and destroy weed seeds. Any weeds that later emerge are hand-plucked so seedlings remain “clean.”
After trees are transplanted into the field, the challenges multiply. Since the crops aren’t harvested for several years to come, there is ample opportunity for both annual and perennial weeds to become established and impede growth. It takes a persistent commitment to hold weeds at bay and keep the trees healthy.
Long-Term Weed Control: A Tale of Two Growing Regions
Long-term weed control can vary significantly across growing regions – evidenced by the strategies used by growers in Oregon and North Carolina, the nation’s top two states for Christmas tree production.
In Oregon, growers tend to plant trees in fields treated to remove weeds like horseweed, horsetail, prickly lettuce, hawksbeard, Canada thistle, wild carrot, and both annual and perennial grasses. The space between rows is often kept bare until tree roots are well established. Later, the row alleyways are planted with a grassy vegetative strip to prevent erosion and to provide a stable soil surface for work crews during harvest.
Common integrated weed control strategies in Oregon range from flaming, mowing and cultivation to hand-weeding, biological controls and herbicides. Preemergence herbicides are typically applied in the spring and summer, followed by a postemergence application to control weeds that escape in the fall.
“The most effective weed management programs in our state blend soil cultivation, herbicides and permanent cover crops to suppress weed populations and reduce the likelihood of herbicide resistance,” says Marcelo Moretti, assistant professor of weed science at Oregon State University.
In North Carolina’s Appalachian region where trees are grown on the sides of hills and mountains, most growers embrace low-growing weeds as a management tool. They strive to establish a groundcover made up of diverse woodland plants like dandelions, clover, wood sorrel, violets and buttercup – either naturally occurring or sown. These low-growing weeds provide a vegetative cover that prevents erosion, adds nitrogen-rich organic matter and impedes the growth of taller weed species that compete with trees, like horseweed, ragweed, foxtail, briar and poison ivy vines.
To keep the groundcover itself from becoming a problem, growers use extremely low-rate applications of postemergence herbicides to suppress its growth. In the fall, they treat tall, problem weeds at the full application rate to keep them from competing with trees.
“It’s a bit of a balancing act, but this two-pronged approach can protect trees, reduce erosion, reduce herbicide and fertilizer use, and create green spaces for native wildlife and pollinators,” Neal says. “The key is to keep the groundcover healthy but keep it in check.”
A Focus on Prevention
Though weed control practices vary by growing region, prevention is vital wherever Christmas trees are grown. Growers work hard to limit the introduction of new weed seeds in the field by cleaning equipment and controlling weeds along farm roads and field borders before they set seed.
They also regularly scout fields and take immediate steps to prevent the spread of problem weeds species, whether through herbicides, cultivation, mowing, hand-weeding or other techniques.
For More Information
Production statistics and other information on Christmas tree crops are available from the National Christmas Tree Association.
About the Weed Science Society of America
The Weed Science Society of America, a nonprofit scientific society, was founded in 1956 to encourage and promote the development of knowledge concerning weeds and their impact on the environment. The Society promotes research, education and extension outreach activities related to weeds, provides science-based information to the public and policy makers, fosters awareness of weeds and their impact on managed and natural ecosystems, and promotes cooperation among weed science organizations across the nation and around the world. For more information, visit www.wssa.net.
Lee Van Wychen
Executive Director of Science Policy
National & Regional Weed Science Societies