Goat's Head Weed Management: Avoiding Puncturevine

One noxious weed that many gardeners deal with is the dreaded goat's head weed. This weed forms a dense mat that covers almost any planting area and causes many problems. Keep an eye out for this plant, especially in garden beds where you grow ground cover.

The first documented case of goat's head weed occurred in California in 1902. Over the decades, gardeners noticed that the noxious weeds formed monocultures that outstripped 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's head weed is up to each of us who grows. Among conservationists, farmers, and ranchers of native habitats, we can reduce the likelihood of this weed invading our gardens, our bare feet, and the feet of our livestock.

So, what is goat's head weed and how to get rid of it? Read on and find out!

What is goat's head weed?

Goat's Head Weed is a fast spreading invasive weed. Source: amadej2008

Goat's Headweed (Tribulus terrestris) is a noxious weed of the caltrop family. Goat's head, cat's head, devil's thorn, pricking vine, devil's eyelash, caltrop weed, and tackweed are the most commonly used common names for Tribulus terrestris. It grows in sandy and rocky locations where the soils drain well. It is one of the most widespread weeds of its kind. Like other members of the terrestris family, it prefers dry, full sun locations. Garbage dumps, ranches, railroad tracks, and pasture lands are all good for these plants. And so is your backyard garden or yard.

Characteristically, goat's head herb is a fast-growing, annual, broad-leaved plant with a deep taproot that has fine rootlets that branch out from the middle. The stems radiate out in a twisting motion, forming a dense mat that clears anything in its path. In foliage-filled areas, the stems may grow erect. Each leaf is divided into 4 to 8 pairs of smaller leaflets. From spring to autumn, 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, a seed pod forms, consisting of 5 spiny ridges called goat heads. The heads have multiple spiked tips that pierce a variety of people, animals, and things. The plant is native to southern Europe and has escaped to many different areas of the world.

Identify goat's head weed

goat head flowerThe goat's head flower is pretty, but a warning of coming thorns. Source: Starr

In the Rocky Mountain states and a garden overgrown with Bermuda grass, the goat's head finds a way to thrive. When young, it can be difficult to identify without its flower. Since the goatshead plant has numerous growth stages in its life cycle, we will discuss how to identify it at each of these stages.

The seedling phase

Tribulus terrestris can resemble other plants in its youngest growth phase. Plants like purslane and spotted spurge are sometimes mistaken for cat's head, although they aren't as polluting. Look for green leaves with gray undersides that have a slightly dented tip. Each leaf should have a prominent midrib and be no larger than 1/4 inch. The stems radiate in a whorl from a central taproot. And the entire plant should not be more than a few centimeters wide.

Mature plant phase

Mostly, Tribulus terrestris grows prostrate, but grows upright among dense foliage. Look out for the distinctive leaves, but note that they may no longer be green as they mature. Instead, these plants can have leaves that are reddish to brown. They will also be covered in hair at this stage. Look for small leaves that are arranged in about seven pairs of leaflets. The stems occasionally branch up to 1 meter wide on either side of the underground taproot.

flowering phase

The bright yellow flower of Tribulus terrestris blooms from spring to autumn. In California, the plant typically flowers from March to October. In Arizona, that's July through September. When the plant typically blooms is largely determined by the regional climate and geology. Each flower has 5 petals and is about as wide as the leaves. If you're wondering if the plant you've chosen is the dreaded goat's head herb, check to see if the flowers are open in the morning. This is when the flower blooms.

reproductive phase

goat head fruitAfter the flowers come the fruit, which wither into a painful, thorny mass. Source: Starr

The flower of the Tribulus terrestris plant blooms, dies, and the plant forms a devil's thorn, or prickly fruit that has multiple prickly tips resembling a goat's head. As the seed pods fall, they become embedded in nearby plant debris, bare feet, and fur. They can also get caught in feet, pierce the bottoms of shoes, or even puncture bicycle tires. That's how they spread so easily. They deprive other plants (especially native plants) of the ability to establish themselves in an ecological niche. Another way goathead weed is so successful has to do with the ability of the seed pod to remain dormant for up to 5 years. This is the main reason why it is widely used all over the world. In the seed production phase of growth, devil's claw reproduces.

Dangers for 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 it affects pets and livestock. While the burrs themselves are harmful and lodge in paws, skin and hooves, the leaves are also a nuisance. They poison livestock if eaten. Sheep in particular are poisoned by the plant. In addition, if a drill is embedded in soft tissue, it can easily cause infection. This can mean a long extraction process or a high vet bill. It is also important that those involved in animal husbandry remove any sharp spines from the skin in which they are embedded, as any remaining residue can also cause infection. This also applies to removing spikes from your skin.

So not only is this plant terrible for people, their clothes and bike tires, it can also cause serious harm to other living beings. Effective control of these plants is therefore important.

How to get rid of goat's head weed

Goat head thornMost often, goat's head thorns sit with a point upwards. Source: aten

Before discussing ways to control goat's headweed, it should be said that treatments that include Epsom salts or even iron salts are not effective herbicides against it. This is because they kill off the foliage along the way, leaving the deep taproot which will continue to produce foliage in the mature growth stage. We'll repeat this in the herbicides section because it needs to be repeated.

Whether you choose natural or mechanical removal methods, or opt for chemical treatment, know you're doing a good job. You'll save yourself from seed heads puncture bike tires and you'll have to resort to antibiotic cream if they get embedded in your hands and feet. You don't want a walk to end badly at the railroad tracks and other places where they are easy to find.

Without chemistry

The Most Effective Way to Control Goat's Head Weeds? Kill them and kill them with fire! Do this with a blowtorch. Apply fire in spring when plants are new or in summer when all plant parts are in place. Simply burn the plants on top of the root mass until sufficiently charred. This will prevent the foliage from returning and will effectively kill the plant. One thing to consider when using fire as a weed killer is to consult local laws before attempting this method. If you're like me and you're in an area that has a burn ban, a propane torch could do more harm than good. Just in case, keep a water hose nearby and water beforehand to prevent the fire from spreading. Always avoid this method on dry and windy days.

An interesting and effective mechanical method is to pull an old carpet behind a vehicle. This is great for people who live on vast tracts of land or even a few acres. As the carpet grinds, it picks up any burrs that are left on the floor. Repeat as needed. And note that you need to combine this method with other methods as it doesn't get rid of plants that are just growing, just the seed pods. But you save a bike 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 out of the ground and expose all of the woody taproot. Slowly pull the plant sideways instead of pulling the plant up as this will surely break the taproot. Breaking off the taproot postpones foliage growth until another time and only provides a temporary fix. Do this by hand or with a weed puller or extractor to save some energy. Then rake the area to remove any remaining seed pods. Use this control method anytime outside of winter when the foliage has died but the taproots remain.

Organic Horny Horny Weed Control

Tribulus terrestrialTribulus terrestris, sometimes called pointworm, is a stubborn weed. Source: gertjanvannoord

Another way to rid your yard, garden or pasture of devil's claw is to release sting weevils. This method works best for people with a lot of land. If you're only dealing with a few plants, it's best to grow them. The weevils feed on stems or seeds, depending on the species. The larvae of Microlarinus lypriformis feed on seeds, while the adult stage of Microlarinus lareynii feeds on the stems. You need both for effective goathead weed removal. Contact your local agricultural advisory office to see if working with weevils is possible. One downside to mass release is that they aren't native insects and don't want to eliminate their habitat, so they don't completely remove the plants you want. They are most effective during the sowing phase.

As we mentioned earlier, iron salt-based organic herbicides will kill goat's head foliage but not the taproot. We do not recommend this as an effective control. Instead, use a white vinegar spray with at least 5% acidity on new plants that haven't set seeds yet. Then lay a tarp over the area where you removed it to kill the taproot. Garden vinegar works similarly but is much stronger at 15% acid. If you have decided to use this as a control, wear protective gear. A ventilation mask and protective goggles are helpful. Don't apply it on a windy day. Horticultural vinegar does not play! You really don't want any of that stuff on your skin or in your eyes. Avoid spraying vinegar on nearby plants. They will die if abandoned. Use this control in summer when plants are fully mature. Rake to remove any remaining seed pods.

Chemical herbicide

Two types of chemical control agents that are suitable for removing goat's head weed are glyphosate and oryzalin. Both types of chemical herbicides are broad-spectrum sprays, meaning they will kill any plants they come in contact with. That is why absolute care is required in the application of chemical control for goat's head. Oryzalin should be used in late winter and early spring. After you spray the area, cover it with a tarp to prevent evaporation in the sun and to protect yourself and your family from exposure to the chemicals. The same goes for glyphosate, except that this chemical weed killer should be applied when the goat's head is fully grown in late spring to fall. Don't apply these intense chemical sprays on a windy day as they can kill nearby plants. Always read the safety labels on these controls before using them. Remember to allow sufficient time between spraying and planting new plants. You don't want to run an entire crop only to have new plants die as a result of exposure to chemicals.

frequently asked Questions

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

Q: Which weed killer kills goat heads?

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

Q: What is a goat head spike?

A: It's a seed pod with a special barb that embeds itself into anything nearby.

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

A: There are several ways to do this, both manually and chemically. Check out the control section above.

Q: Will goats eat goatshead weed?

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

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