Goat head seeds

Goat head or Puncture Vine (Tribulus terrestris)-Time to Get Rid of the Them

This noxious weed, an invasive species from southern Eurasia and Africa, is a menace to people, pets, livestock and bike tires. Known for their horrible spiny seeds, these pea-sized mace balls are sharp enough to puncture thin-walled tires of bikes and wheelbarrows and inflict great pain to any creature that steps on them. Hungry livestock will eat the poisonous plants when pastures are overgrazed.

2020 infestation of goat head weed next to the sidewalk along the south edge of Franklin Miles Park. The seeds will create a huge problem for dog walkers as the seeds will spread out all over the place including the sidewalk.

Even with the feeble start to our monsoon season, the rain has caused the seeds to germinate and the goat head population has gone from zero to sixty in just a few short weeks. Now is the time to get out there and weed them out. If you wait more than a few more weeks, the goat head seeds will have already started to ripen ensuring that they will be a hazard and keep coming around each summer. Seeds can live in the soil for at least 5 years, so don’t let this weed grow unchecked or you’ll have a very difficult time getting rid of it.

Goat head vine grows from a single taproot at the center of the plant. Being an annual, if you cut off the plant from the root or pull it, that will kill the plant. A 2 person team approach is very productive. One person standing cuts the plant from the root with a shovel (it only takes one well-placed slicing chop under the center of the plant) and the second person picks them up and bags them.

Some folks say they will just spray the weeds with an herbicide, but that doesn’t kill the seeds or prevent the dying plants from ripening seed before they perish. Physically removing the plants is mandatory.

To keep them from coming back, a deep layer of heavy mulch (but not straw), 2 to 3” thick will prevent the seeds from germinating and smother any small seedlings that might have been overlooked when pulling/cutting them.

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Northern Arizona Invasive Plants

a northern arizona homeowner’s guide to identifying and managing invasive plants


Common name(s): Goathead, puncturevine

Scientific name: Tribulus terrestris

Family: Caltrop family (Zygophyllaceae)

Reasons for concern: This plant easily outcompetes native plants, resulting in dense monocultures and a reduction in native plant diversity very important to wildlife and pollinators. The seeds germinate quickly and can lie dormant in the soil for many years, prolonging the life of an established population. Sharp burrs cause serious injury to people, pets, wildlife, bicycle and vehicle tires, and livestock, and are easily spread by vehicles, pedestrians, and animals, resulting in even larger populations.

Classification: Non-native. Included on the Arizona Noxious Weed List as a Class C noxious weed, which means it is widespread and “may be recommended for active control based on risk assessment.”

Botanical description: Mat-forming, fast-growing broadleaf plant.

Leaves: Each small, hairy leaf is subdivided into 4 to 8 pairs of smaller leaflets, opposite each other on stems.

Stem(s): Grows low to the ground, forming dense mats 2 to 5 feet in diameter. Can grow almost erect in dense vegetation. Hairy, trailing stems radiate out from a central point at the taproot.

Flowers: Bright yellow, with five petals. Appear in the axil, where the leaf meets the stem. Open only in the morning. Blooms July through September.

Seeds: Seedpod is a cluster of 5 flat spiny burrs, containing up to 5 seeds. It breaks apart at maturity.

Roots: Deep taproot branching into network of fine rootlets.

Native to: Southern Europe

Where it grows: Dry or gravely sites. Roadsides, waste places, pastures, fields, railroad tracks. Prefers dry, well-drained, sandy sites below 7,000 feet in elevation.

Life cycle: Summer annual

Reproduction: By seed Goathead habit.

Weedy characteristics: Goathead thrives in hot and dry conditions where other plants cannot. Its dense mat smothers out other species. It can start flowering within 3 weeks of germination, and continues to flower all summer. Depending on the moisture available, it typically produces 200 to 5,000 seeds in one growing season. Seeds can remain dormant in the soil for 5 years. Its roots are hard to remove.

Control strategies: Do not let them flower and go to seed! Prevent the seeds from spreading. Seedlings are easy to remove by hand pulling, and older plants can be pulled or dug out. Rake or sweep up any burrs that may have dropped. Tilling can be effective before seed production. Frequently monitor a population for new plants. Plant desirable native species to outcompete invasives. Herbicides are effective on small, actively growing plants. Contact your local county extension office for more information on chemical control.

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