Q: What is the best way to get rid of puncturevine? I have a couple of patches that have shown up in my yard.
A: This is a weed I battle every summer as folks bring us the gift of this seed into our farm area their shoes. The annual weed puncturevine (Tribulus terrestris) also known as goat heads, grows in a mat and produces many harmful spiked seeds. Acaricide Factory
Here is how the University of California (U.C.) describes this pesky weed: “Puncturevine produces many burs (burrs) with sharp spines that can injure humans and animals, as well puncture bicycle tires. (It’s) leaves contain compounds called saponins, which can be toxic to livestock, especially sheep, when eaten in quantity.”
One plant can produce 300 to 5,000 seeds per season, and can grow in mats up to five feet, so it’s definitely a weed you want to start controlling as soon as you see it sprouting up in your yard.
The most effective way to eliminate this weed is to pull it up by hand or use a hoe to cut the plant off the deep taproot. Try to do this while it’s still in the flower stage, before it seeds.
If you have plants going to seed you can still pull them up. Just wear thick gloves to avoid injury to your hands, and try not to shake seed heads off the plant.
Don’t add these plants to your compost pile. The seeds will survive most composting processes.
Seedling plants can also be lightly tilled under, but I don’t recommend tilling plants with seeds heads as this may bury the seeds and increase chances of germination.
Mulching landscape beds with at least three inches of mulch, or a weed barrier that screens out all light, can also be an effective method to eliminate this weed. This needs to be done during the winter and early spring, before the weed sprouts. Be warned that if the puncturevine sprouts on top of the mulch it can still grow due to a very long tap root.
Master Gardeners don’t recommend chemical control for this weed unless you have a large area that is infested and it’s difficult to access for tilling the seedling plants under.
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The puncturevine I have recently been pulling up is too mature for control with an herbicide for this summer, as it already has seeds and is past the stage where it’s effective to use a chemical control.
If you plan to use an herbicide for control next year, mark where the plants are growing this summer and apply a pre-emergence herbicide to the site before the seeds germinate, or spray with herbicide right after germination.
The U.C. pest note for puncturevine states, “there are few pre-emergent herbicides that are effective. Products containing oryzalin, benefin, or trifluralin will provide partial control of germinating seeds. These must be applied prior to germination (late winter to mid-spring). After plants have emerged from the soil (postemergent), products containing 2,4-D, glyphosate, and dicamba are effective on puncturevine. The smaller or younger the plant, the better the post-emergent herbicides work.”
As always, when using a herbicide, read and follow all label directions.
For more information on the life cycle and how to identify this weed, go to the U.C. puncturevine pest note at https://bit.ly/3edFc2V.
Knockout Weed And Grass Killer The Shasta Master Gardeners Program can be reached by phone at 242-2219 or email mastergardener@shastacollege.edu. The gardener office is staffed by volunteers trained by the University of California to answer gardeners' questions using information based on scientific research.