Caltrop (Tribulus terrestris)

Caltrop aka Bindy-eye or Cathead, is a flat, prostrate annual weed that produces spiky burrs. It is common in areas of frequent Spring and Summer rain, and each plant can produce up to 20,000 seeds per plant. It occurs in all Australian states except Tasmania.

After you finish reading this, you will be able to:

• Identify Caltrop, Cathead or Bindy-eye.
• Know the habitat of Caltrop or Cathead.
• Know the best cultural and chemical options for Bindy-eye or Cathead.

 

The seeds of Caltrop germinate after Summer rain, when the maximum air temperature reaches 24°–27°C. Seedlings grow quickly, flower and form new burrs within three to five weeks. Plant growth is rapid, and a deep root system develops in a few weeks. It has a low need for water and can survive for long periods without water.

The fruit of Caltrop consists of a woody burr with sharp, rigid spines, which splits into segments when ripe. Each of these segments has four hard spines, and two of these are shorter than the other two.

Caltrop has numerous prostrate green to reddish brown stems radiating from a crown and central taproot. These stems are long (up to 2 m in length), wiry and covered in fine hairs.

Caltrop is toxic to stock and can cause nitrate poisoning and staggers, and make livestock skin sensitive to light (photosensitive). Caltrop also has allelopathic (inhibitory) effects on other plants, and its spiny burrs damage the feet of livestock and injure humans.

In late Spring and Summer after rainfall Bindy-eye germinates as soil temperatures increase. Through the Summer after rainfall events there is a
succession of germinations. Growth is rapid and in only a few weeks a deep root system develops.

 

Caltrop is an annual prostrate herb that spreads by seeds, and has reddish brown, wiry stems covered with fine hairs. These stems spread out for up to 2 metres from a woody taproot. On the stems, the leaves are made up of several leaflets which are opposite each other. The leaves are fern-like and greyish-green.

Flower: The flowers of Bindy-eye or Cathead are short-lived (lasting a single day), have five petals, and are yellow, and 8 to 15mm in diameter. Caltrop flowers from Spring to Autumn.

Category: Broadleaf (Dicot).

Height: Caltrop is prostrate.

Leaf length: The leaves are 5-12 mm long.

Leaf width: Leaves are 3-5 mm wide and have very small stalks.

Reproduction: Caltrop reproduces from seed. It can regrow from its taproot which can grow to a depth of 2.6 m and has numerous fibrous laterals.

Comments: Caltrop leaves are darker on the upper surface than on the lower and arranged in 4 to 8 pairs of opposite, oblong leaflets. The lower surface of the leaves can appear silvery due to the presence of hairs. A single plant can produce up to 20,000 seeds a season, and this can remain viable for up to 5 years.

Habitat: Caltrop prefers warm-temperate regions on light-textured soils. Where there is little competition, and has become a weed of cultivated crops, lawns, playing fields, roadsides and neglected areas.

Its presence is a strong indicator for low calcium, potassium and organic matter, or high phosphorus, magnesium, iron, and aluminium. More information on lawn and turfgrass weeds is in our weed ID chart.

 

 

 

Both cultural and chemical control will remove Caltrop from your lawn and turfgrass. Using only herbicides as the control method is impractical
and it is better to combine spraying with cultural control.

 

 

Caltrop is a poor competitor. So if your turf is healthy, dense, and actively growing, it goes a fair way toward preventing this weed from becoming established.

Bare areas are its friend, so the best plan is to avoid them, so maintain a dense, full turf canopy to prevent this weed getting a foothold.

If it is present and not too widespread, then hand-pulling Caltrop is effective. However, if you hand-pull this weed, it is important to remove the tap root as otherwise it will regrow. The best way to do this is to pull from the root crown, in order to remove the tap root.

The burrs readily attach to the feet and pelts of pets, shoes, mowers, and any machinery that is placed on it. This means it is important to clean shoes and machinery when you move out of areas of Caltrop infestation.

 

 

 

 

Chemical control is best from March to May and October to December. You need to treat this weed before seeds set, and you need to repeat this every time the seeds germinate. Several post-emergent herbicides are available for Caltrop control. At Gilba Solutions, we recommend ProForce Contra M herbicides. (Don’t use Contra M on Buffalo grass.)

Non selective options include Glyphosate (Rapid Fire 800). If you use this and water quality is an issue then we recommend the use of ProForce Manta Ray.