Weevil-Minded Goathead Control

Southwest Yard & Garden

By Dr. Marisa Thompson with guest contributor Dr. Leslie Beck

 

Deceptively "cute" yellow flowers and compound leaves of the dreaded puncturevine. Photo from Quay County Cooperative Extension Service (https://aces.nmsu.edu/county/quay/weeds/common-weeds-of-quay-cou.html).

Question: I moved here from Massachusetts last August and was late in identifying the cute plant with the yellow flowers as the source of so much pain for myself, my daughter, and my cats. I heard about weevils that attack this weed. Should I try to get some?

- Pamela

Answer: It sounds like you’re experiencing the joys of puncturevines (aka goatheads). Welcome to the Land of Enchantment! Note: “goatheads” is pronounced “goat-heads,” not “goa-theads” like my friend said when she first moved here.

Those pretty yellow flowers are deceptive. The only good thing about getting a few dozen goatheads stuck in the soles of your shoes is the opportunity to do a little sarcastic tap dance. I call it the Puncturevine Shuffle.

The NMSU Extension Weed Specialist Dr. Leslie Beck, NMSU Extension Entomology Specialist Dr. Carol Sutherland, and I have written several columns about puncturevine problems, including “The Early Bird Catches the Weed,” “Get Your Goat(heads): Control Puncturevine Before it Controls You,” and “Dodder: To Kill or Not to Kill” (those are clickable links!).

I invited Dr. Beck to tell us more about this weevil wonder that’s offering a glimmer of hope in our collective consciousness: “Ah yes, puncturevine. It is definitely the time of year for goathead inquiries—and injuries. Your interest in the puncturevine weevil as a biocontrol agent is understandable. When it comes to weed management, biological control is a good tool to have in your tool belt, if available for your target weed. There are actually two puncturevine weevils: one that bores into the stem and one that eats the seeds. Alas, they just don’t cause enough damage at a quick enough pace to control the weed all by themselves. The stem weevil doesn’t stop the development of flowers (which quickly form seeds). And the seed weevil, probably already in your soil feeding on goathead seeds, are not feeding at a fast enough pace to prevent germination. 

[I'm not sure which is the lesser of two weevils. ;) ]

“Long story short, you most likely already have both of these biocontrol weevils feeding on your puncturevine as we speak, and they’re helping, but they won’t have the ability to control the weed by themselves. It’s not ecologically smart for the little buggers to kill their host and then be without habitat or sustenance. Thus, they don’t. As a result, I wouldn’t recommend trying to find additional populations of the weevils to introduce into your yard. They are already pretty prolific in New Mexico.

“Luckily, puncturevine is one of those summer annual weeds that responds well to physical damage and removal without the use of herbicides. They have a shallow root system, and the stems cannot root as they spread, so the entire mat of a single plant can be traced easily back to the central taproot and removed. [Easily, but not painlessly.]

“The important thing to consider with summer annual weeds like puncturevine is to manage them before seeds develop. When you see flowers, think of them as a red alert to kill the plant now before it’s too late and a new generation of seeds has been sown. This is especially important for puncturevine since the seed can live for 7 or more years in your soil prior to producing a plant.”

Multiple garden tools can help with puncturevine control, from hula hoes (aka scuffle or stirrup hoes) to weed-whackers. Wear personal protective equipment if you use a powered weed-whacker, or you’ll be sorry—those devil seeds fly like ninja stars. I’m a big fan of the Hori Hori gardening knife and the heron weeder, formerly known as the hooke ‘n crooke, and I get a spark of joy when flipping goathead mats upside down to shrivel in the sun with the exposed taproots pointing straight up in the air.

Dr. Beck warns, “It will be pretty labor-intensive at first, but if you are consistent in your practices in removing the plant before seed production you will notice the populations diminishing and getting easier to manage as the years progress.”

           

           

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook page (@NMDesertBlooms)

Please copy your County Extension Agent and indicate your county of residence when you submit your question!

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms.