Pine trees might be a pretty sight, but this invasive tree can easily take over due to its large root system.
When cutting the trees down is not an option, many look to powerful herbicides to do the trick – so how does the popular product Roundup fare?
Will Roundup kill pine trees? Roundup can effectively kill small and mature pine trees due to the active ingredient glyphosate. This chemical compound blocks the shikimic acid enzyme pathway, preventing vital proteins from forming. Roundup can be applied as a foliar spray or deposited directly into the tree’s vascular network.
Roundup is used by gardeners and forest managers alike, but it needs to be used with caution to avoid damaging plants you still wish to keep!
Here are our tips for using Roundup precisely on small and large pine trees, plus alternative tree-killing methods, and more.
How To Kill a Pine Tree With Roundup
Roundup can be an effective pine tree herbicide, but it will require different application styles to ensure an efficient job depending on the tree’s age.
How Does Roundup Work?
Roundup contains the compound glyphosate which, when absorbed through a plant’s foliage, stem, or trunk, obstructs the production of important enzymes.
This chemical also binds tightly to soil particles, allowing it to persist for many months.
How Long Does Roundup Take To Work?
Roundup can take 7-14 days to kill most plants and small trees down to the roots when sprayed all over, or it can take several weeks to 6 months to take down mature trees.
Method #1 (For Small Trees)
Pine trees no larger than 4 feet can be killed by spraying their foliage.
- Wearing appropriate protective gear, use the highest concentration recommended, and spray the entirety of the tree’s foliage from all angles using the hand-held sprayer provided.
- Before application, ensure that no leaves are covered with rainwater, frost, or snow as this will hinder absorption.
- Apply the Roundup around mid-late summer when pines are in full-leaf to ensure the best coverage.
Method #2 (For Mature Trees)
For larger trees, you will need to make holes deep into the bark (penetrating the cambium layer just beneath) to deliver the herbicide internally, increasing the absorption rate.
- Donning protective clothing/eyewear, drill four to six 1/2-inch holes around the base of the trunk (approximately 12 inches from the ground).
- Drill the holes at a downward, 45-degree angle, and make each hole around 1-1½ inches deep.
- Two inches below this first set of holes, drill another four to six holes at the same downward angle and depth.
- Next, fill a garden sprayer with liquid glyphosate (containing 41% concentration). Hold the spray nozzle ½ an inch away from the drilled holes, and fill each with the herbicide.
This drill-and-fill method typically sees large trees dying within 6 weeks – taking up to around 6 months in total.
How To Use Roundup Safely Under Pine Trees
If you need to kill plants and weeds growing under a wanted pine tree, it’s important to hand weed where possible to avoid damaging the tree roots.
Do not use Roundup to kill tree suckers as this can damage the tree itself. Instead, remove them by hand.
If you do need to use Roundup, here’s how to do so safely:
- Avoid spraying Roundup on windy days to prevent the spray drift coming into contact with tree roots/foliage.
- If using liquid concentrate glyphosate, use the lowest possible dilution as advised on the label to reduce the amount accumulating in the soil.
- Set the Roundup spray tank pressure to its lowest setting, and keep the nozzle close to the target plant/weed to prevent splashback or wind carry.
- Place a protective weed barrier around the tree – this can be made from woven or fleece material.
How To Kill a Pine Tree (Without Roundup)
For those of you who would prefer to avoid using Roundup whenever possible, there are several other effective options for getting rid of unwanted pines.
In high doses, sodium inhibits chlorophyll production by choking the flow of magnesium and potassium.
Drill several ½-inch holes into the trunk (explained above) at a downward angle, making the holes at least 3 inches deep.
Make a solution of 2 parts Epsom salt and 1 part water, and pour it into the holes.
Standard white vinegar contains acetic acid that burns through foliage, disallowing vital nutrients to travel to the tree roots.
Drilling 3-inch deep holes as before, fill and re-fill the holes with vinegar as needed (alternate this with the salt method for faster results!).
The Ringbarking Method
Wearing protective eyewear, remove a complete belt or ring of bark around the tree using a chisel, hammer, or chainsaw. The ring created should be around 4-8 inches wide.
Ringbarking (also called banding or girdling) without herbicide can obstruct nutrient flow to the roots and branches, but you can also apply Japanese Knotweed control or Tordon 22K to the exposed ring for more effective results.
Killing the Stump
This involves tying a bag around a pine tree stump to cut off its water and sunlight supply.
Band a black plastic/garbage bag around the stump, covering the top and diameter entirely, and place some bricks and heavy rocks on top to weigh it down.
In 3-6 months, the stump will begin dying. Prune off any sprouting seedlings and use additional stump removal solutions to speed up the rotting process.
Does Roundup Kill Tree Roots?
The active weed-killing compound in Roundup (glyphosate) can be extremely damaging when absorbed by tree roots.
Glyphosate interferes with the root’s ability to take in several vital nutrients that help the tree withstand disease and recover, causing root rot to set in.
Will Roundup Kill Oak Trees?
Killing oak trees with Roundup requires spraying the entire foliage of small trees or applying the herbicide directly to the vascular system of larger oaks by drilling holes in the trunk.
Mature oaks may require stronger higher-concentration herbicides containing triclopyr to be most effective.
Roundup can severely weaken a pine tree, killing it within a matter of weeks or months depending on the size
Small pines can be eradicated with a foliar spray, while mature pines will require a drilling and injection method to absorb the herbicide efficiently.
You can also kill pine trees without Roundup by using vinegar, salt, and girdling methods.