GOATHEADS - Tribulus Terrestris: Bane of Bowsers and Bicycles

Stan Hill

Tribulus terrestris is an annual plant, meaning it grows anew each year from seed. Germination usually begins soon after last frost.  Two-to-three weeks after germination, new seeds form and continue to be produced up to first frost.  Seeds are relatively heavy in relation to their size, so are not spread by wind but readily catch rides on any passing foot (animal or human) or tire to generate new vines.  

While proliferation of tribulus terrestris seems limitless and control impossible, it ain’t necessarily so!   

A dense carpet of puncture vines once lined the sides of a well-used path and draped over the wall like a waterfall.  Three large trash bags of vines were removed and left the ground littered with Goat Head thorns.  By all logic, real control would be hopeless.

But NO tribulus terrestris vines were found in this spot for the next six years, and the few plants found in years seven and eight would barely fill a small grocery sack. It appeared a feasible level of control could be achieved.  

To test this puncture vines were removed at various spots and monitored year-to-year—with similar success at each location.    To further evaluate effectiveness, vines in an adjacent low traffic area were left undisturbed to compare to the cleared areas.  Cleared areas remained free of caltrops, while the untouched area continues to produce numerous vines – demonstrating that removal of puncture vines can significantly impact control of Goat Head thorns.

Knowing what the plant looks like to differentiate it from other plants is primary to getting rid of goat head thorns. While a few gardeners and other folks know what puncture vine looks like, a lot of people do not—including many who are most affected: dog walkers and bicyclists.   To recognize tribulus terrestris: 
1)  It is a prostrate vine, meaning: tendrils grow very close to the ground.  Hence, mowing has little or no effect, other than to help spread the seeds.  (However, mowing may still help make the plants easier to find amongst taller growth, even if it spreads the seeds.)       
2)  Tendrils radiate outward from a central taproot, like spokes of a wheel.  
3)  It has small yellow flowers with five petals. Other low growing plants may have yellow flowers, but tribulus terrestris also has distinctive leaves.  
 4)  Leaves are one to two inches long with a pinnate leaf pattern (small leaflets grow opposite from a central stem, like veins of a feather; pinnate=feather like). Pinnate leaf patterns are common in trees and shrubs, but seen in only a few low-growing plants. 

On the rare occasion of another low-growing plant with little yellow flowers and pinnate leaf pattern, the clincher is to look underneath the leaves for clusters of thorns.   At first glance it is easy to confuse other low growing plants for tribulus terrestris. While they may look similar, they DO NOT produce goat head thorns.   Despite the similarities, tribulus terrestris is quite distinctive and quickly becomes identifiable, even when growing among other plants.
 
A Pie-in-the-Sky Proposal
Successful goat head mitigation is achievable. One person can make a significant difference, and many people working together can make a community free from the invasive noxious weed— tribulus terrestris Challenge: Each person who walks a dog, rides a bicycle, or has tracked home a thorn and sees a patch of puncture vine in their neighborhood along a public right-of-way — spend just one hour removing those vines (and monitor the same area the following year). 



PULLING GOAT HEAD VINES 
Puncture vines can be pulled with the root intact, particularly if vines are small and green and soil is loose or damp (some people advocate flooding an area with water before pulling). While effective, pulling vines may present unfortunate encounters between fingers and thorns (which even pierce thick gloves).  It is just as effective to cut the taproot and then pick up the vine with a pair of pliers to put in a bag.  Bladed tools like knives and hand weeders work well to cut the root, as do trowels, shovels and hoes.

While pulling the vines is a very effective and environmentally friendly way to subdue tribulus terrestris, other methods may also be useful, particularly in very large areas. Goatheads.com (http://www.goatheads.com/) has information about herbicide sprays, puncture-vine eating weevils, a propane weed-burner (for loose and dry goat head thorns on the ground), and thorn resistant shoes for dogs.
 
Bent Fork 2016-4 - August/September 2016

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