What is Puncturevine?
Puncturevine (Tribulus terrestris) is a summer annual forb, and is native to Europe. The plant is prostrate or ascending, spreading into mat forming cover.
How to Identify Puncturevine
The stems are trailing and can grow to 1 1/2 to 5 feet long. Leaves are formed into leaflets, with each leaflet containing 5 to 8 oval leaves. The leaves are hairy and opposite. The flowers appear in July through October. They have five petals and are yellow in color. Each flower node will produce a fruit, at maturity the fruit will break into 5 seed capsules. Each seed capsule will produce 2-4 seeds. Each capsule is hard and contains many spines, almost tack like. The shape of the seed capsule has been referred to as a “goathead.” The seeds will propagate after the first moisture of the spring and then any wet period following. Seeds can stay viable for 4 to 5 years.
Effects of Puncturevine
In spite of its generally prostrate habit, puncturevine is a serious competitor with crops, particularly in dry conditions where its ability to extract moisture from great depths is an advantage. The seed capsules can cause injury to humans, animals, and tires. Seeds can be found in hay, which may cause injury to animals. The capsules can also become entangled in wool, and decrease the quality.
The most successful biological control agents for puncturevine are Microlarinus lareynii, a seed feeding weevil, and Microlarinus lypriformis, a stem boring weevil. M. lareynii and M. lypriformis have been collected from established colonies around the state. Redistribution of M. lareynii and M. lypriformis is available upon request. Microlarinus are normally shipped mixed together in containers of 100-200 adults depending on availability, which can vary year to year.
- Are puncturevine weevils the right answer to my puncturevine problem?
Every situation is different, but in general, if you have only a few puncturevine plants in your yard it is much easier to pull the plants before they set seed or just take a shovel and pop the plant out at the base before seed set. You don't usually have to pull them out by the roots. Since puncturevine is an annual plant and only reproduces from seed, if the plant has already put a lot of energy into growing and may even be flowering, it will usually not have enough energy to regrow from that severed root crown. The weevils are used more for larger acreages that have too many puncturevine to pull or treat. Remember that a biocontrol agent does not usually eliminate a weed completely because it will have nothing to feed on, so there will almost always be a few weeds left, but they will hopefully be reduced to a manageable level.
- What else do puncturevine weevils attack?
Puncturevine is the only plant in Colorado that the weevils will attack. They cannot reproduce on other plants found in Colorado.
- Will the weevils kill puncturevine?
The stem weevil can slow the growth of the puncturevine plant, but will not usually kill the plant. Since each puncturevine plant can produce thousands of seeds that may remain dormant for several years, this can be a very difficult weed to control.
- How long will it take to control my puncturevine?
As with all biocontrol agents, Microlarinus can take several years to show results and will probably never totally eliminate puncturevine. With time, and along with the use of other integrated pest management tactics such as hand pulling of plants before seed formation, puncturevine weevils can bring the weed population down to an acceptable level.
- How can I order puncturevine weevils and is there a charge?
You can place an order on the Request-A-Bug page. Puncturevine weevils sell for $30 per release of 100 weevils.
- What is the best release site?
Release the weevils directly onto growing puncturevine plants. We do not recommend releasing the weevils onto plants that will be sprayed with herbicides.