Asthma Weed (Euphorbia hirta)
Asthma Weed is also known as Hairy Spurge or Cat’s Hair. Cat’s Hair is a Summer annual soft leaf plant. It produces several spreading to upright red stems that are up to 40 cm tall. These stems have a cover of yellow hairs and contain a milky sap.
After you read this, you will be able to:
- Identify Hairy Spurge (Euphorbia hirta).
- Know the habitat of Hairy Spurge.
- Know the best cultural and chemical options to control Asthma Weed.
The sap of Asthma Weed is toxic if eaten. It causes photosensitive skin reactions and severe inflammation on contact with the eyes or open cuts.
You often find Euphorbia hirta in turf or in plant beds. However, you can also find it in cracks in pathways and in between pavers.
Being a semi-tropical and tropical warm season weed, Hairy Spurge does not tolerate frosts. I prefers warm and sunny locations but it also grows in dense shade.
Asthma Weed has its name because it is used to treat asthma and several lung diseases. This plant is also effective against worms, dysentery and colic, warts, asthma, bronchitis and dengue fever.
The distribution map is courtesy of The Atlas of Living Australia.
How to Identify Asthma Weed.
Hairy Spurge is an annual stemless or short stemmed weed. It has a tap root, and a basal rosette of leaves that are about 500 mm across. As it grows, it sends out stolons, and quickly spreads across the ground.
The taproot of Euphorbia hirta is up to 60 cm long but is usually only 15 to 20 cm long. The rest of the root is made up of fibrous roots that grow off the main taproot.
Category: Broadleaf (Dicot).
Photosynthetic Pathway: Asthma Weed is a C4 Weed.
Flower: Hairy Spurge flowers from the Spring to the Summer. You find the flowers in in the upper leaf forks. The flowers have a green/yellow/creamy colour that look like dense round clusters.
Height: It grows up to 40 cm high.
Leaf length: Asthma Weed has paired leaves which are 4 to 50 mm long. These leaves have a dark green to red colour with purple markings. They are on short stalks about 1 to 3.5 mm long, and have a fine-tooth margin.
Leaf width: The leaves are 2 to 24 mm wide.
Reproduction:
Asthma Weed reproduces by seed, and its creeping stems that root at the stem joints. When mature, the seed pods explode and disperse the seeds.
A mature plant can produce several thousand seeds over just 8 to 10 weeks. Cat’s Hair germinates at temperatures of between 24 °C and 29 °C, but it can germinate at any time when the temperatures are over 16 °C.
Populations of Asthma Weed can rapidly build up becuase:
- It germinates over a wide temperature range.
- It has a life cycle that takes only about 60 days from germination to seed set.
Comments: Both the upper and lower leaf surfaces have a cover of close-lying hairs. As the plant matures it loses those on the upper leaf surface.
Habitat: Hairy Spurge is a weed of verges, footpaths, lawns, bare areas, and sports fields.
Asthma Weed is a good indicator weed of compact soil, and bare or thin lawns.
For more information check out our weed ID Chart to Identify Weeds by photo.
How to Control Asthma Weed.
You can control Cat’s Hair by cultural and chemical means.
Cultural Control of Asthma Weed.
- If you hand weed it can be effective but you must remove all the roots, and dispose of them to avoid any re-growth.
- This must be done every 2 to 4 weeks because of its fast growth rate, and the ability of Asthma Weed to quickly produce seed once it germinates.
- Due to its prostrate growth habit, mowing is not effective to manage Cat’s Hair.
- Euphorbia hirta thrives in thin or bare areas so grass selection is important. You should take mportant factors such as shade, climate and the amount of wear into consideration.
Chemical Control of Asthma Weed:
Pre-Emergent Control of Euphorbia hirta.
There are currently two products with a Cat’s Hair registration in Australia. These are BASF Freehand and Envu Esplanade.
- BASF Freehand only suppresses this weed.
- Envu Esplanade is a pre-emergent for use around railroads, roadsides, industrial sites and utility corridors.
Overseas there are more options available for Asthma Weed,
- Dithiopyr, Metalochlor, Pendimethalin, Oxadiazon all suppress Cat’s Hair.
- Prodiamine has a label for suppression and long term control.
Post Emergent Control of Asthma Weed.
Most broadleaf herbicides will control this weed, but options in Australia are limited. We have personally had success with the use of ProForce Warhead Trio and saw results within 2 weeks.
Non Selective Control of Asthma Weed.
- Glufosinate-ammonium provides control for 4 to 6 weeks. However, it then regrows and recovers due to the limited movement of glufosinate.
- Glyphosate. You can use Glyphosate but if water quality is an issue then use ProForce Manta Ray.
The following are non-selective but also have a long term residual and stop any re-growth of Euphorbia hirta.
- Renegade. Renegade stops germination of Asthma Weed for up to 12 months. This reduces the need for multiple herbicide applications.
- Numchuk Quad. This gives post and pre emergent Hairy Spurge control for up to 12 months.
- Cortex Duo. Cortex Duo gives a rapid knockdown of Cat’s Hair, and residual control for up to 3 months. It is also safe to use around trees.
Non Selective Control of Asthma Weed.
Product | Active | Chemical Group | Rate/Ha |
Glufosinate 200 | Glufosinate-ammonium | 10 | 1-6L |
Rapid Fire 800 | Glyphosate | 9 | 0.9-1.35 Kg |
Numchuk Quad | Terbuthylazine + Glyphosate + Amitrole Oxyfluorfen | 5 + 9 + 34 + 14 | 20-25L |
Cortex Duo | Nonanoic Acid + Oxyfluorfen | 14 | 7L/1000L |
Renegade | Bromacil | 5 | 3.5-6.5Kg |
