Goat head stickers are the common name for the hard, spiny burrs produced by the Puncturevine plant, Tribulus terrestris. This aggressive weed, native to southern Europe, thrives in dry, disturbed soil. The painful burrs cause pain to people and pets when stepped on. They can easily puncture bicycle tires and thin car tires, earning the plant its other common name, caltrop. Eliminating Puncturevine requires a persistent, multi-faceted approach targeting every stage of its growth cycle.
The Puncturevine Life Cycle
Puncturevine is a summer annual weed, completing its life cycle within a single growing season by reproducing by seed. Germination begins in late spring or early summer, and the plant quickly develops a deep taproot to tolerate dry conditions. It grows low to the ground, forming dense, prostrate mats that can spread several feet in diameter.
The plant begins flowering and producing spiky burrs within three to five weeks of germination, continuing until the first frost. Each yellow flower develops into a cluster of five hard burrs, which break apart into individual, sharply-spined units. A single large plant can produce thousands of seeds that remain viable in the soil for four to five years or longer. This long-term viability creates a seed bank, requiring consistent control.
Physical Removal Techniques
For smaller infestations, physical removal is the most immediate and effective method, provided it is done before the plant sets seed. Hand pulling is straightforward, but it is best done when the soil is moist to ensure the entire taproot is extracted. If the plant is pulled after the burrs have formed, bag the entire plant and any loose burrs immediately to prevent further spread.
Using a specialized shovel or a hoe to cut the plant off at the base of the taproot is efficient for larger areas. Cutting the stems usually prevents the plant from regrowing, especially if done before it flowers. For collecting dropped burrs, dragging an old piece of carpet, a burlap sack, or a specialized roller across the area can be effective.
Thermal methods offer a chemical-free way to deal with weed seeds in bare ground. Solarization involves covering the infested area with clear plastic sheeting during the hottest months to kill the seeds and plants underneath. Propane flaming can also be used to quickly kill young seedlings, though it does not affect seeds already buried in the soil.
Using Herbicides for Control
Herbicides offer a solution for larger infestations, but timing is paramount. They are divided into two main types: pre-emergent and post-emergent.
Pre-Emergent Herbicides
Pre-emergent herbicides form a chemical barrier in the soil that prevents seeds from germinating. These products must be applied in late winter or early spring, before the Puncturevine seeds sprout. Active ingredients such as oryzalin, benefin, trifluralin, or pendimethalin offer partial control. Disturbing the soil after application breaks the chemical barrier, allowing new seeds to germinate.
Post-Emergent Herbicides
Post-emergent herbicides are applied directly to visible plants after they have emerged from the soil. They are most effective when the Puncturevine plants are small and young. Effective ingredients include 2,4-D, dicamba, and glyphosate. Products containing 2,4-D and dicamba are suitable for turf areas because they kill broadleaf weeds without harming the desired grass. Glyphosate is non-selective, killing nearly all plants it contacts, reserved for spot treatments. Never apply post-emergent sprays once burrs have matured, as the herbicide will not prevent the formed seeds from dropping.
Preventing Future Infestations
Long-term management requires depleting the persistent soil seed bank. Any removed plants, especially those with burrs, must be disposed of properly by bagging and sealing them to prevent the seeds from spreading. Throwing the plants into a compost pile without proper sealing can contribute to the infestation elsewhere.
Changing the environment to make it less hospitable is an effective preventative measure, as the plant prefers bare, disturbed, and sunny soil. Applying a thick layer of mulch, ideally three inches deep, blocks sunlight and suppresses seed germination. Establishing dense turf or other desirable ground cover helps shade the soil and compete with the weed for water and nutrients.
In some regions, biological control agents have been introduced to manage large-scale infestations. These agents include the Puncturevine Seed Weevil (Microlarinus lareynii) and the Puncturevine Stem Weevil (Microlarinus lypriformis). The seed weevil destroys seeds within the burr, while the stem weevil tunnels into the plant’s stem. While these weevils offer long-term population suppression, they are a management tool, not an immediate elimination solution.