Puncture vine is a broadleaf summer annual that loves disturbed areas and vacant lots and thrives in hot and dry conditions. It will also truly enjoy growing in a garden if a seed finds its way there. It germinates in the spring to mid-summer with soil moisture and warmer temperatures and once growing, seems to endure everything.
Goathead plants are low growing and can spread two to five feet or more from a central taproot. The plant has leaves that grow opposite each other with four to eight pairs of leaflets on a stem, and can produce yellow flowers with five petals as soon as three weeks after germination. Seed pods are produced as a group of four to five spiny burrs that separate out into single burrs with two or more sharp spines each. Seeds can remain viable from five to 20 years and a plant can produce 200 to 5,000 seeds a season.
When controlling puncture vine the goal is to reduce the number of seeds on or in the soil, which means stopping the plant from flowering and producing seeds. In small areas, try hoeing or hand-pulling, but make sure you cut off or pull up the plant below where the top attaches to the tap root. You can also mulch areas to keep the seeds from germinating. While there are also a couple of biocontrols, including a seed weevil and a stem weevil, I am not aware of either of these overwintering in our area, which limits their effectiveness. Some people have had luck using propane burners to destroy viable seeds on the soil surface.
There are some pre-emergent herbicides that can help control these plants if they are used early enough – before the seeds germinate. However, any of these would also stop most other seed growth, whether good or bad, so don’t plan to plant seed in areas where you are using these chemicals during that growing season. Two types of pre-emergents to consider include oryzalin and trifluralin.
Once the plant is growing, control is similar to most other broadleaf plants. In areas without other plants you could use glyphosate (found in Round-Up) and in turf you could use 2,4-D and/or dicamba. As is the case with many weeds, controlling young plants is easier than controlling older plants. Due to the amount of seeds a plant can produce it will take time, but if you stay steady at it you can see the day when no new plants appear.
Thought for the day: “Plant and your spouse plants with you, weed and you weed alone.” — Jean-Jacques Rousseau.
For more information about these topics call the Utah State University Extension Grand County office at 259-7558 or email Mike Johnson at firstname.lastname@example.org.