Tribulus terrestris, commonly known as puncturevine or goathead, is a member of the caltrop family. The name caltrop comes from an ancient iron weapon used to incapacitate war horses and other war animals and refers to the barbs on the plant's burs. This vicious weed infests poor soils and areas where cattle have overgrazed leaving bare spots.
Description
Puncturevine is an annual weed that is infamous for its sharp, thorny burs that cause painful injuries to humans and animals and damage tires. This low-growing plant forms a dense mat that can spread up to 15 feet in diameter. The leaves resemble tiny fern foliage. The central leaf stem has four to eight pairs of hairy leaflets, each about 1/2 inch long. The 1/3-inch yellow flowers bloom in late spring and early summer. They are followed by a fruit that later breaks into tack-like structures that contain the seeds. Each plant produces up to 500,000 fruits, which each produce four or more seeds. (
Seed Disbursal
The tack-like structures that contain the seeds are called nutlets. The nutlets have thorns that adhere to a variety of surfaces. They are picked up by animal fur, feathers and feet, and also by human shoes, clothing and tires. Each seed is viable in the soil for three to seven years.
Prevention
Puncturevines thrives in poor, bare soil, and improving the soil is an important step in controlling the weed. Amend the soil with compost and plant grass or a dense groundcover to prevent its growth.
Natural Control
A few plants are easily removed by digging or hoeing beneath the crown. Remove the plants early in the season, before they have a chance to set seeds. If the plants are already producing burs, sweep the area after removing the weeds, then go over the soil with a nappy cloth or piece of carpet to remove any remaining burs. For large areas, burn the plants with a propane torch. This method does not always prevent the weed from returning and is only used in areas so large that digging the individual plants is impractical.
Biological Control
Two weevils, Microlarinus lareynii, which attacks puncturevine seeds, and Microlarinus lypriformis, which attacks the stems, are effective in controlling puncturevine when used together. Some agricultural extension services distribute these insects free of charge.
Chemical Controls
Use preemergent herbicides containing trifluralin in late winter or early spring. Once puncturevine has emerged, use a selective herbicide. Make sure the herbicide is labeled for use against Tribulus terrestris, and follow the instructions for safe and effective use.
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