Caltrop (Tribulus terrestris) is a summer growing weed that reproduces from seed. It is a major contaminant of produce and is dangerous to animals.
- prostrate weed with green to red-brown stems that radiate for up to 2 metres from the central taproot
- leaves consist of several pairs of opposite leaflets, 5-12mm long and 3-5mm wide, leaves may be hairy or almost smooth
- upper surface of the leaves is grey-green, undersides are paler
- flowers are 8-15mm in diameter with five bright yellow petals
- flowers open in the morning and close or shed their petals that afternoon
- fruit is a woody burr 1cm diameter, with sharp rigid spines to 6mm long
- ripe fruit splits into 5 wedge-shaped segments with two pairs of spines, containing up to 4 seeds
- seeds are yellow, ovoid in shape and 2-5 mm long
- taproot is long, slender and branched, there are many fibrous lateral roots.
Why is it a problem?
- burrs can damage animal feet and injure humans
- burrs can also contaminate produce such as dried fruit and wool
- toxic to stock and can cause nitrate poisoning, photosensitisation and staggers
- may also chemically inhibit the growth of some other plants.
- Eyre Peninsula – widespread with broadacre infestations
- Northern pastoral – common in most towns
- Northern agricultural districts and Yorke Peninsula – widespread
- Murray Mallee – widespread
- South East – common in all towns and in north, scarce in south
- Central region – widespread on the Adelaide Plains.
- most abundant on light sandy soils but will grow on almost any soil type
- seeds germinate after late spring and summer rains and the plant grows rapidly flowers appear within three weeks of germination, fruits in 5-6 weeks
- flowering continues for several months
- plants die off in autumn or early winter, as they are sensitive to frost
- Caltrop seeds germinate in several batches (staggered germination) throughout the summer, making control very difficult.
How it spreads
- mainly spread by seed, burrs attach to animals, clothing and machinery.