Weeds

Goat Head Weed Control: Preventing Puncturevine


Goat head weed

One noxious weed a lot of gardeners deal with is the dreaded goat head weed. This weed forms a dense mat that overtakes almost any planting area and causes a lot of problems. Especially among garden beds where you grow ground cover, look out for this plant. 

The first recorded instance of goat head weed occurred in California in 1902. As the decades went on, horticulturists noticed the noxious weed formed monocultures that outcompeted native plants. This led to the classification of the plant as an invasive species. 

With that in mind, identification and removal of the dreaded goat head weed are on every one of us who grow. Among native habitat conservationists, farmers, and ranchers, we can reduce the chance of invasion by this weed into our gardens, our bare feet, and in the feet of our livestock. 

So, what is goat head weed and how do you get rid of it? Read on, and find out! 

What Is Goat Head Weed?

Goat head weed
Goat head weed is a rapidly-spreading invasive weed. Source: amadej2008

Goat head weed (Tribulus terrestris) is a noxious weed in the Caltrop family. Goat’s head, cat’s head, devil’s thorn, puncture vine, devil’s eyelashes, caltrop weed, and tackweed are the most frequently used common names given to Tribulus terrestris. It grows in sandy sites and rocky locations where soils are well-draining. It is one of the most widely distributed weeds of its kind. Like other members of the terrestris family, it prefers dry areas in full sun. Waste places, ranches, railroad tracks, and pasture land are all well-suited for these plants. And so is your backyard garden or yard. 

Characteristically, the goat head weed is a fast-growing, annual broadleaf plant with a deep taproot that has fine rootlets branching from the center. The stems radiate in a twisting motion forming a dense mat that takes out anything in its way. In foliage-filled areas, the stems can grow upright. Each leaf is subdivided into 4 to 8 pairs of smaller leaflets. In the spring through the fall, small bright yellow flowers bloom in the morning. Each flower has five petals and emerges from the leaf axis. After the flowers bloom and die away, a seedpod forms, composed of 5 spiny burrs called goat heads. The heads have multiple spiny points that puncture a myriad of people, animals, and things. The plant came from Southern Europe and has escaped into many different areas of the world. 

Identifying Goat Head Weed

Goat head flower
The goat head flower is pretty but is a warning of thorns to come. Source: Starr

In Rocky Mountain states, and a Bermuda grass-covered yard, goat’s head finds a way to thrive. When it’s young, it may be hard to identify without its flower. Because the goat’s head plant has numerous growth phases in its life cycle, we’ll discuss how to identify it within each of those. 

The Seedling Phase

Tribulus terrestris can resemble other plants in its youngest growth period. Plants like purslane and spotted spurge are sometimes confused with cat’s head, although they aren’t as ecologically damaging. Look for green leaves with grey undersides that have a slightly indented tip. Each leaf should have a prominent midvein and will be no larger than ⅗ of an inch. The stems radiate from a central taproot in a whirling manner. And the entire plant should be no wider than a few inches across. 

Mature Plant Phase

Most of the time you’ll find Tribulus terrestris growing prostrate, but among dense foliage, it will grow upright. Look for its characteristic leaves, but note that in the mature phase they may no longer be green. Instead, these plants can have leaves that are reddish to brown. They will also be covered in hairs at this stage. Look for small leaves that are arranged into about seven leaflet pairs. The stems will occasionally branch out to 1 meter wide on either side of the underground taproot.  

Flowering Phase

From spring to fall, Tribulus terrestris’ bright yellow flower blooms. In California, the plant typically flowers from March to October. In Arizona, that’s July to September. When the plant typically flowers is largely determined by the regional climate and geology. Each flower has 5 petals and spans about the same width as the leaves. If you’re wondering if the plant you’ve singled out is the dreaded goat head weed, check to see if flowers are opened in the morning. This is when the flower blooms. 

Reproductive Phase

Goat head fruit
After the flowers come the fruit, which dries into a painful thorny mass. Source: Starr

The Tribulus terrestris plant flower blooms, dies away, and the plant forms a devil’s thorn or a spiny fruit that has several spiny points which resemble a goat’s head. As the seed pods fall, they get embedded in nearby plant debris, bare feet, and fur. They can also get caught in feet, pierce the bottom of shoes, or even puncture bicycle tires. That’s how they spread so easily. They eliminate the ability of other plants (particularly native plants) to take hold in an ecological niche. Another way goat head weed manages to be so successful has to do with the seed pod’s ability to remain dormant for up to 5 years. This is the chief reason it’s found widely around the world. The seed production phase of growth is where the devil’s claw reproduces. 

Dangers to Pets and Livestock

Now that we’ve discussed the life cycle of this noxious weed, it’s worth discussing the importance of its removal, and how that relates to pets and livestock. While the burrs themselves are damaging and get embedded in paws, skin, and hooves, the leaves are also a nuisance. They poison livestock if they’re consumed. Sheep, especially, are subject to poisoning by the plant. Furthermore, if a burr gets embedded in soft tissue, it can easily cause infection. This could mean a long process of extraction or a hefty vet bill. It’s also essential that those involved in animal husbandry remove all of the sharp spines from the skin it’s embedded in as remaining debris can also cause infections. This goes for removing spines from your skin, too. 

So not only is this plant terrible for humans, their clothes, and bicycle tires, it can cause grave damage to other living beings. That’s why effective control of these plants is important. 

How to Get Rid of Goat Head Weed

Goat head thorn
More often than not, goat head thorns sit with one spike pointed upward. Source: aten

Before we discuss the ways to control goat head weed, we should say that treatments that involve Epsom salts or even iron salts aren’t effective herbicides against it. That’s because they incidentally kill the foliage leaving behind the deep taproot, which continues to produce foliage in the mature stage of growth. We will reiterate this in the herbicide section because it bears repeating. 

Whether you decide to use natural or mechanical methods of removal, or you turn to chemical treatment, know you’re doing the good work. You’ll save yourself from seed heads that puncture bicycle tires, and make you resort to antibiotic cream when they embed themselves in your hands and feet. You don’t want a stroll by the railroad tracks and other places where they are readily found to end badly. 

Without Chemicals

The most effective method for controlling goat head weeds? Kill them and kill them with fire! Do this with a blowtorch. Apply fire in the spring when plants are new, or in summer, when all parts of the plant are present. Simply burn plants at the top of the root mass until they’re sufficiently charred. This prevents the foliage from returning and effectively kills the plant. One thing to consider with using fire as a weed killer is to consult local laws before trying this method. If you’re like me, and you’re in a region with a burn ban in effect a propane torch weeder could cause more harm than benefit. Keep a water hose nearby just in case and pre-water to prevent the spread of fire. Always avoid this method on dry and windy days.

One interesting and effective mechanical method involves dragging an old carpet behind a vehicle. This is great for people who live on vast expanses of land, or even a few acres. As the carpet drags, it will pick up any burrs that remain on the ground. Repeat the process as needed. And note you’ll need to combine this method with other methods as it doesn’t get rid of plants that are currently growing, just the seed pods. But you’ll save a bicycle tire or your foot in the process. 

Another method that works very well, but requires a lot of effort is to manually pull the plant from the ground, unearthing the entire woody taproot. Slowly pull sideways rather than pulling the plant upwards, as this will surely break the taproot. Breaking off the taproot defers foliage growth to another time, providing only a temporary fix. Do this by hand or via a weed puller or extractor to save some energy. Then rake the area to remove any remaining seed pods. Use this control method at any point outside winter, when the foliage has died away but taproots remain. 

Organic Goat Weed Controls

Tribulus terrestris
Sometimes referred to as puncturevine, Tribulus terrestris is a stubborn weed. Source: gertjanvannoord

Another way to rid your yard, garden, or pasture of the devil’s claw, is to release puncture vine weevils. This method is best for people with a lot of land. If you’re just dealing with a few plants, pulling them is best. The weevils feed on stems, or seeds depending on the species. The Microlarinus lypriformis larvae feed on seeds, while Microlarinus lareynii feed on the stems in their adult stage. You’ll need both for an efficacious elimination of goat head weed. Consult with your local agricultural extension office to see if working with weevils is possible. One downside to releasing them en masse is they’re not native insects and they won’t want to eliminate their habitat, so they don’t completely remove the plants you want them to. They are most effective during the seeding stage. 

As we mentioned before, organic herbicides based on iron salts kill goat head foliage, but not the taproot. We don’t recommend those as effective control. Instead, use a white vinegar spray with at least 5% acidity on new plants that haven’t set seed yet. Then lay a tarp over the area where you’ve removed them to kill the taproot. Horticultural vinegar works similarly but is a lot stronger at 15% acidity. If you’ve decided to apply this as a control, wear protective gear. A ventilation mask and goggles are helpful. Do not apply it on a windy day. Horticultural vinegar does not play! You truly do not want any of this stuff on your skin or in your eyes. Avoid spraying vinegar on nearby plants. They will die if they’re exposed. Use this control in summer when the plants are at full maturity. Rake to remove any seed pods that remain. 

Chemical Herbicide

Two types of chemical control suited to removing goat head weed are glyphosate and oryzalin. Both types of chemical weed killers are broad-spectrum sprays, meaning they will kill any plants they make contact with. That’s why absolute care in the application is completely necessary with chemical control for goat’s head. Oryzalin should be applied in late winter and early spring. After spraying the area, cover it with a tarp to prevent evaporation in the sun, and to protect yourself and your family from contact with the chemicals. The same goes for glyphosate, except that this chemical weed killer should be applied when the goat head is full-grown in late spring through fall. Do not apply these intense chemical sprays on a windy day, as they can kill plants nearby. Always consult the safety labels on these controls before using them. Remember to allow adequate time between spraying and planting new plants. You don’t want to go through an entire planting only to have new plants die as a result of contact with chemicals.

Frequently Asked Questions

Prostrate growth habit of Tribulus terrestris
Tribulus terrestris has a prostrate growing habit in sandy soil conditions. Source: Jim Morefield

Q: What weed killer kills goat heads?

A: Chemicals like glyphosate and oryzalin work, as well as strong white vinegar and horticultural vinegar. Consult the safety labels on these controls before using them. 

Q: What is a goat head thorn?

A: It’s a seed pod with a specialized barb that embeds itself in whatever is around. 

Q: How do you permanently get rid of goat heads?

A: There are several different ways to do this, both manual and chemical. Check out the control section above. 

Q: Will goats eat goat head weeds?

A: Yes. Livestock are attracted to this plant. However, goats are less susceptible to poisoning, unlike their relative, the sheep.

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