Cocklebur Identification: And Why It Is Seriously Toxic

The burr is the identification

Cocklebur burrs are oval, roughly one to two centimetres long, hard, brown when ripe, and covered in stiff hooked spines. Each burr contains two seeds. They are painful to handle and they cling to anything fibrous.

Burdock burrs are much larger, rounder, and covered in hooked scales rather than spines. They look like a small brown velcro ball. Burdock leaves are also enormous and woolly white underneath, where cocklebur leaves are triangular and rough.

Burweed and Noogoora burr are also Xanthium species with similar burrs, so the genus is easy once you have the burr. The species comes down to leaf shape and where it is growing.

If you have found the burr, you are nearly done. The leaf confirms it.

The plant itself

The toxicity, without softening it

Cocklebur contains carboxyatractyloside, and it is most concentrated in the seeds and the young seedlings. The seedling stage is the dangerous one, because seedlings emerge in bare ground and pasture, look like ordinary seedlings, and are attractive to grazing animals.

The clinical picture is severe: liver damage, vomiting, weakness, and death in livestock within a day or two of a significant dose. Cattle and horses are the usual victims, and pigs and sheep are also affected. Documented losses are common where cocklebur grows in pasture or gets into hay and grain.

For people, the risk is lower simply because nobody eats it, but the seeds are toxic and children should not be handling burrs and then putting fingers in their mouths. Wash your hands after handling.

The other practical risk is physical rather than chemical. The spines are painful, they break off in skin, and they cause infections if not removed.

Getting rid of it

• Wear thick gloves and eye protection. The burrs hurt and the plant is toxic.
• Pull before the burrs form. That is the single most effective thing you can do, because one plant left to seed produces hundreds of burrs.
• Bag it and put it in the rubbish, not the compost and not the green waste. Burrs survive composting and green waste gets spread on land.
• Do not strim or slash it. Strimming scatters burrs and spreads the problem.
• If livestock are on the paddock, remove the plants before they seed and keep animals off the area while seedlings are emerging.
• Check hay and grain for burrs before feeding it, because contamination is a common route onto a property.
• Follow up. The seeds stay viable in the soil for years, so expect seedlings for several seasons.

Why the burr is so effective

The hooked spine is one of nature's better designs. Each spine has a tiny hook at the tip that catches in fur and fabric and releases only when pulled in the right direction.

Velcro was developed by studying exactly this mechanism, and burdock rather than cocklebur is usually credited. The principle is the same.

The practical consequence is that cocklebur spreads along animal trails, fence lines, paddock gates and anywhere a dog walks. If you find it in one corner of a property, check the routes in and out, because that is where it arrived and where it is going next.

Most of the plants on this site are a curiosity. Cocklebur is not. This is one where getting it wrong has killed cattle and horses, and where the seedlings are a genuine hazard because they come up in pasture and look like nothing in particular.

The plant spreads by burrs — the hooked, spiny things that stick to socks, dog fur and tractor tyres. That is the part people pick up and photograph, and it is also the part that makes the identification easy.

So the burr comes first, then the toxicity, then how to get rid of it.