Caltrop (Tribulus terrestris).

Caltrop aka Bindy-eye or Cathead, is a prostrate, warm season annual weed that has spiny burrs. It is common in areas of frequent Spring and Summer rain, and is in all Australian states except Tasmania.

In NSW it is common in the Central West slopes and North West slopes because:

• They have good Summer rainfall.
• High Summer temperatures and sunlight intensity.
• The soils are fertile.

After you read 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.

 

Why is Caltrop a Problem?

Caltrop is a problem weed because:

• Each plant produces up to 20,000 seeds.
• Its seeds remain viable for up to 5 years.
• It is adapted to a wide range of climates.
• It has a very deep taproot that is up to 2.6 m long.
• It has a low water requirement and survives for long periods without any water.
• Cathead also has allelopathic effects on other plants.
• The spiny burrs of Caltrop damage the feet of livestock and injure humans.
• Caltrop is toxic to stock, and causes nitrate poisoning and staggers. The nitrate poisoning makes the skin of livestock sensitive to light (photosensitive).

 

How to Identify Caltrop.

Caltrop is an annual prostrate herb that spreads by seeds, and has red to brown, wiry stems with a cover of fine hairs. The stems spread out for up to 2 m from a crown. The stems leaves are made up of several opposite leaflets.

Flower: The flowers of Bindy-eye or Cathead only last a single day, and have five yellow petals, that are 8 to 15 mm in diameter. Caltrop flowers from Spring to Autumn.

Category: Broadleaf (Dicot).

Photosynthetic Pathway: Caltrop is a C4 Weed.

Height: Caltrop is prostrate.

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

Leaf width: Cathead leaves are 3 to 5 mm wide, and have very small stalks.

 

Caltrop Reproduction.

• Caltrop reproduces from seed that germinate after Summer rain. In drought conditions as little as 25 mm of rain is enough for the seeds to germinate. This small amount of rain maintains a Tribulus community for 8 weeks.
• It needs relatively high temperatures to germinate, and a daily maximum temperature above 29°C is ideal. When the maximum air temperature is 24° to 27°C there can be several germinations
• At these temperatures, germination begins within 6 to 8 hours and does not need light. Seedlings germinate from a depth of up to 5 cm in sandy soils, but not this deep in heavy soils.
• Caltrop produces up to 20,000 seeds a season, and these are viable for up to 5 years.
• The fruit of Caltrop comprises a woody burr with sharp, rigid spines, which splits into segments when ripe. Each of these segments has four hard spines, and two are shorter than the other two.
• When Caltrop fruit is on the ground, one of the spines always points upwards. These attach to animals, tyres, and shoes.
• Once the seedlings emerge, they flower within 3 weeks. They then continue to flower for several months if the plants are not killed by drought.
• Caltrop or Bindy-eye also regrows from its deep taproot if shoot damage occurs from cultivation or herbicides.

 

Comments: The uppersides of Caltrop leaves are darker, and arranged in 4 to 8 pairs of opposite, oblong leaflets. The undersides appear silvery due to the presence of hairs.

Habitat: Caltrop is a weed of warm regions and light soils. You find it in crops, lawns, sportsgrounds, and waste areas.

Caltrop indicates low soil Ca or high P, Mg, Fe, and Al.

More information on 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. This is because Cathead does not tolerate shade.

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 you can handpull Caltrop. 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.

 

There are a succession of germinations with this weeds over the Summer, and its growth is rapid. This means that more than one spray application may be necessary, and you should time spray applications so that the majority of the weed has been sprayed before seeding occurs.

Thankfully, there are several options for Caltrop control as it has not evolved resistance to herbicides. The problem with Caltrop is not being able to kill it. Instead its the rapid seed germination, and the succession of germinations that occur when suitable conditons exist.

Chemical control is best from March to May and October to December.

 

Pre-Emergent Control of Caltrop.

There are several pre-emergent options for Cathead.

• Pendimethalin (ProForce Battalia 435),
• S-Metalochlor.
• BASF Freehand Herbicide suppresses it.

 

Post Emergent Control of Caltrop.

Several post-emergent herbicides are available for Caltrop control. If multiple germinations occur several repeat sprays are needed. This is because the plant only needs a month to produce viable seed.

The best time to spray for Cathead or Caltrop is in the Spring and Autumn, when the plants are small, actively growing and not under stress.

• 2,4-D. This tends to burn the top of Caltrop but it then grows back.
• Warhead Trio. Safe on Buffalo grass.
• Contra M herbicide. Don’t use Contra M on Buffalo grass.
• MCPA.
• Weed Blast MA. Safe on Buffalo grass.
• Casper Turf. Registered in South Africa for Caltrop. Don’t use Casper Turf on Buffalo grass.
• Dicamba. Don’t use Dicamba on Buffalo grass.
• Slinger 240.

 

Non Selective Control of Caltrop.

Non selective options for Caltrop include:

• Glufosinate-ammonium provides control for 4 to 6 weeks, but it regrows and recovers due to the limited movement of glufosinate.
• Glyphosate. You can use Glyphosate to control Cathead but if you use Glyphosate, and water quality is an issue then use ProForce Manta Ray.

 

The following are non-selective but also have a long term residual, and stop re-growth of Caltrop.

• Renegade. Renegade stops the germination of Bindy-eye for up to 12 months, and reduces the need for multiple herbicide applications.
• Numchuk Quad. This gives effective post and pre emergent Cathead control for up to 12 months.
• Cortex Duo. Cortex Duo gives a rapid knockdown of Caltrop, and residual control for up to 3 months. It is also safe to use around trees.