Every year, as it starts to warm up, the weeds get a head start. This year, the “games” are beginning earlier with the mild weather that we are having. The good news with this drier weather is that you can actually be outside surface cultivating to head off major weed infestations by disturbing the surface of the soil. It’s not too muddy and you can actually be in the yard without the clay sucking the boots off your feet!
While there are many weeds that need constant vigilance, not many of them warrant as much early and ongoing effort as the puncturevine does. Also non-affectionately called “goathead” or “devil’s thorn,” the puncturevine’s Latin botanical name of Tribulus terrestris is highly accurate; the meaning of the Latin is pretty clear to even the casual observer. “Terrestris” means “of or from the earth” and “tribulus” means trouble or tribulation. If there is a well-earned name, this is it!
Puncturevine is a member of the caltrops botanical family. It gets its name from the fact that caltrops were instruments of ancient warfare; spheres with sharp points or spikes pointing outward. They were cast onto battlefields or roads to cripple horses and foot soldiers. Grisly and effective, today’s goathead bears a striking resemblance to this ancient weaponry.
Bicyclists, bare-footed children, and people out of a stroll with rubber “flip-flop” footwear all know too well the damage and pain these persistent weeds cause. They have a very effective growth habit; low, mat like, small yellow flowers, and are very invasive in warm climates. The weed thrives in hot and arid regions, allowing it to out-compete native plants for water and nutrients. It tends to get a foothold in disturbed or marginal crop land. Given an artificial water source, it will really take off. This is easily seen along irrigation ditches and ditches near paved roads where water runs off.
The burrs are not toxic, but livestock can get sick from eating the leaves and stems, especially sheep. I suspect they would do so only out of desperation, so having more delectable alternatives would probably eliminate any desire to eat caltrop. If the burrs are ingested, they most likely will cause damage as they pass through the mouth, throat, gut and, uh, exit point of the animal. Nasty stuff.
The burrs are easily spread by their ability to readily attach to footwear, animal coats and fur, tires and nooks and crannies in machinery. More challenging, the seed heads are viable for an estimated two to seven years. Some people say they can germinate for up to 20 seasons! Given the right conditions the plant can produce, from its central growing crown, several branches of more than six feet. The more plant stems and leaves, the more burrs. Each plant can produce between 200 and 5,000 of our little pointed friends (if only I could get my carrots to grow so readily!).
Seed heads begin green and soft, as the season progresses they become hard, brown and somewhat brittle. It has outwardly curving thorns which become sharper as the fruit dries. The burr comprises five parts, each with seeds in it. The seed matures and “waits” for the nexus of warmth, moisture, soil depth, and open sky.
Almost paradoxically, it will not compete well when there are a lot of other things already growing and shading it out. With all the energy it requires to spread and create copious amounts of seed, it needs a lot of direct access to sunlight. Put it in the shadows and you’re on the way to controlling it. This is why you will see this pest flourish at the edges of marginal lawn areas, but not so much in a well-established and healthy lawn, or where there is little soil disruption.
If you do get an infestation, fast action is the best offense. Ignoring the problem will not make it go away. It’s easy to get mesmerized by the large mats of greenery covering bare earth. Don’t be fooled; it will only be a short time before the goatheads show up in en masse. The later it is in the season, the more likely the goathead fruits are to detach when the plant is disturbed. So like most weeds, early elimination is highly superior to trying to control the weed after it has reached maturity.
If you had a serious outbreak of goatheads last year, it’ll be back in the spring, but you can control it. You’ll need to be make sure the area has adequate water to get the seed heads to sprout. If we continue to have a dry winter, you may actually need to water the area as soon as the weather starts its warming cycle for the season (probably April or May). Get those little seedlings started early in the season. Then spray them with a good broadleaf weed control, or use a propane torch to kill the seedlings. Of course, you will need to be very careful to not ignite flammable materials or harm structures and other items. Killing vegetation this way is called “flaming.” When flaming weeds, you don’t need to char or obliterate them; simply keep the flame on the plant long enough that you see the plant turn glossy, release moisture through vapor and slightly shrink or wilt. This takes a second or two and large areas can be covered rapidly.
If you are spraying a chemical, only do so when it’s calm outside. You want the herbicide to coat only the intended target, and not drift to other desirable plants. I find that early morning is best before the day’s breezes start up. If you really want to protect pollinators, spray early in the evening, as the weed’s flowers are only open in the morning. This will allow the herbicide to be absorbed away from the leaf surfaces before the friendlies start buzzing around the next day.
If you do hoe or pull up the weed to control them, and the plants already have burrs forming on them, don’t leave uprooted plants behind. Immature thorns will continue to mature, even after the plant is out of the ground. If the thorns are dry and are easily detached, use gloves to move the plant to a trash container and manually pick up thorns remaining on the ground. I find the most convenient way to dispose of them is to put them in the trash container. If you have a recreational fire pit, you can burn them as well.
Has this weed always been with us? Nope. It is not native to the U.S., and was most likely brought in with grain imports or on the fur of animals. It appears to have originated in Africa and Eurasia. However, goatheads have been with us for some time; the first infestation was reported in California in 1903. So, puncturevine looks like it arrived about 30 years after Russian thistle, more commonly known as “tumbleweed.” Now that’s a dynamic duo if there ever was one!
Even with all the characteristics we don’t like about puncturevine, it does have a rich history in indigenous medicine from many of the world’s cultures and is still commonly used in alternative medicine today. It is used to treat maladies such as high blood pressure, kidney problems, low libido, erectile dysfunction, high cholesterol, anemia and digestive orders. I’ve found many testimonials to the efficacy of caltrop. If so, how’s that for making lemonade from lemons, so to speak?
Like many things in life, puncturevine is a lot easier to manage when the problem is small. Get ahead of it and make your yardscape a lot it more enjoyable while also preventing it from spreading to your neighbors. Owning an issue early on, addressing it and moving forward is sound advice, both for weed control and for life in general.
It’s a great day for a walk. I think I’ll put my thick-soled shoes on before I head out, just to be safe.
Jay Cooper can be contacted at firstname.lastname@example.org, or you can visit his website at dirtfarmerjay.com for videos and articles on gardening, shop skills, culinary arts and landscaping.