Pine trees can serve a variety of purposes in a home landscape, from acting as windbreaks to providing visual interest with their evergreen foliage. Though generally low-maintenance, pine trees can develop weeds beneath their canopy that need to be managed. Whether you’re dealing with invasive grasses, broadleaf weeds or climbing vines, effective weed control is necessary for the health of your pine tree. But it’s important to approach weed management with care, as herbicides can harm or kill pine trees.
Below, three tree experts Brady Self from Mississippi State University Extension Service, Jaret Rushing and Jacob Hackman from the University of Arkansas Systems Division of Agriculture and Jacob Hackman from the University of Arkansas Systems Division of Agriculture share their top tips for killing weeds in pine trees.
Can Weeds Growing on a Pine Tree Hurt the Tree?
In certain cases, weeds growing on a pine tree can hurt it. But this will depend on the type of weeds and the age and health of the pine tree.
Young pine trees are vulnerable to low-growing weeds like invasive grasses and broadleaf weeds that compete for sunlight, water and nutrients. But this risk passes once saplings grow tall enough. “As the tree gets older and establishes itself above competing vegetation, the impact of those weeds goes down exponentially to a point where there is very little impact on the growth or survival of the tree,” Self says.
But, older, more established pine trees can still be impacted by weeds. Unwanted trees, technically weeds, compete with pine trees and suppress their growth. “Any plant can be considered a weed if it’s growing in an area that it shouldn’t be,” Hackman says. “Although it sounds strange to think of trees as weeds, some species are invasive or can have devastating effects on overall forest health and should be removed or managed to maintain a healthy pine tree or forest.” Hardwood trees and pine tree saplings sprouting too close to established trees are common types of weed trees that grow under pines.
Climbing weeds are also a concern with older pine trees. Weeds like English Ivy, Virginia Creeper, Oriental Bittersweet and Kudzu can smother trees with their vines and leaves while blocking out sunlight. In extreme cases, the weight of the vines can cause tree limbs to break under their weight. “Vine control is important because climbing vines can choke out pine trees,” Rushing says, “and vines that have reached the canopy compete for resources with the tree.”
Can Weed Killer Kill Pine Trees?
Yes, weed killers can absolutely harm or kill pine trees, so they must be used carefully. “The wrong chemical applied in the wrong way can have devastating effects on a forest ecosystem and should be treated with the utmost respect and caution,” Hackman says.
“Always read the product label and “ask someone in the know if you are unsure of potential damage to pines,” Self says.
How to Kill Weeds in Pine Trees Without Killing the Pine Tree
To kill low-growing weeds in pine trees, like invasive grasses or broadleaf weeds, use a foliate-activated weed killer like glyphosate, the active ingredient in Round-Up. This type of herbicide only works when applied to living foliage, so it poses a low risk to pine trees. To avoid harming the tree, “apply it underneath tree foliage, and take care not to get it on the needles,” Rushing says.
There are other safe, natural weed killers available if you’re uncomfortable with glyphosate.
For larger weeds, like invasive trees, use a chainsaw or hand saw to cut them down. Wear protective gear and follow all safety protocols. Even when cut down, weed trees can return, requiring further action. “Many species of trees can resprout from the root system that remains underground,” Hackman says. He suggests trying a method called “hack and squirt,” where you create a wound in a tree trunk with a chainsaw or axe and then quickly spray herbicide into the wound. “[This] can be effective in completely killing the weed tree, but the time of year for this type of treatment can change its efficacy,” he says.
To remove invasive Norway Maple tree saplings from my yard, I use a reciprocating saw with a pruning blade. After cutting the sapling down, I dig away the soil from the roots and cut the roots with the saw as well. This is effective at preventing regrowth at the stump, which this tree species will often do.
Preventing climbing vines from getting established requires vigilance as they grow quickly. When young, pull them up by the root to remove them. To kill established climbing weeds, cut them down with loppers, remove as much of the root as possible and apply glyphosate to any remaining foliage or growth.
When Should I Call a Pro?
While killing weeds in pine trees is typically a manageable task for homeowners, there are some scenarios where you should call a pro.
If you have allergies to the weeds you’re trying to control, call a pro to avoid exposure. Also, if weed trees are taller than 10 to 15 feet tall, it may be best to hire a professional to safely fell them for you.
Still unsure you can tackle this on your own? Hackman recommends reaching out to local consultants. “Almost all 50 states have local county agriculture or forestry agents that can come perform a site visit to help or point you in the right direction free of charge. Most states will also have local Consulting Foresters and Arborists who are trained in herbicide applications and can perform the application for a fee,” he says.
About the Experts
- Brady Self is an Extension Professor with the Mississippi State University Extension Service and has over 20 years of professional forest herbicide experience.
- Jaret Rushing is a Forestry Extension Instructor with the University of Arkansas Systems Division of Agriculture and has over 17 years of experience.
- Jacob Hackman, PhD. is an Assistant Professor of Forest Management and Extension with the University of Arkansas Systems Division of Agriculture. Tips for killing weeds around pine trees without damaging their roots or healtheasy solutions for homeowners!
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