Control Goatheads (Puncturevine) tips

by Masters Gardeners of Shasta County
Q: Puncturevine has shown up in my yard this past year and I would like to know the best way to eliminate it.
A: Puncturevine is often spread by people as they pick up the spiked seeds on the sole of their shoes and then leave the “gift” of a seed in our yards.
This annual weed Tribulus terrestris, also known as goat heads, grows in a mat and produces many spiked seeds that are harmful to our feet and bike tires.
Here is how the University of California (UC) describes this pesky weed; “puncturevine produces many burs with sharp spines that can injure humans and animals, as well puncture bicycle tires.
“In addition, 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 a season, and can grow in mats up to five feet, so the sooner you can control this weed the better chance you have to eliminate it.
The most effective way to eliminate this weed is to pull them up by hand or use a hoe to cut the plant off at the deep taproot. Try to do this while they are still in the flower stage before they seed.
If you have plants going to seed you can still pull them up, just wear think gloves to avoid injury to your hands and try not to shake seed heads off the plant. Also, do not add these plants to your compost pile as the seeds will survive most composting processes.
Seedling plants can also be lightly tilled under but I do not 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. Note that puncturevine sprouts later than other weeds as they need warm soil temperatures to germinate so do not be lulled into thinking that you no longer have this weed just because it does not come up with other weeds in the spring.
Also be on the lookout for puncturevine seedlings that sprout on top of the mulch as they can still grow due to a very long tap root sent down to the soil below.
Master Gardeners do not recommend chemical control for this weed unless you have a large area that is infested, and it is difficult to access for tilling the seedling plants under.
Herbicides work when the plant is in the seedling stage but once the puncturevine starts to flower it may be too mature for control with an herbicide as the mature plant leaves develop a waxy coating that sheds herbicide spays.
If you plan to use an herbicide for control, your best strategy is to mark where they are growing this summer and apply a pre-emergence herbicide to the site before the seeds germinate or spray with an herbicide right after germination.
The UC pest note for puncturevine states “there are few preemergent 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 midspring).
“After plants have emerged from the soil (post emergent), 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 an herbicide read and follow all label directions.
For more information on the life cycle and how to identify this weed, go to the UC puncturevine pest note at http://ipm.ucanr.edu/PMG/PESTNOTES/pn74128.html