Asthma Weed (Euphorbia hirta)
Asthma Weed is also known as Hairy Spurge or Cat’s Hair. It is a weed of the semi-tropics and tropics, and does not tolerate frosts.
This is a Summer annual weed that has very soft leaves. It produces several red stems that can be up to 40 cm tall or spread close to the ground. These stems have a cover of yellow hairs and contain a milky sap.
- It has its name because people use it to treat asthma and lung diseases.
- This plant is also works against worms, dysentery and colic, warts, asthma, bronchitis and dengue fever.
Why is Asthma Weed a Problem?
- Although it is a short lived plant, it is fast-growing, and outcompetes plants for water, light and nutrition.
- Each plant produces hundreds of seeds, which disperse easily.
- It has a quick life cycle. This means it can quickly produce seeds.
- It is very adaptable to environmental conditions. It tolerates poor soils, high temperatures, and even shade.
- The sap of this weed is toxic if eaten. It causes photosensitive skin reactions, and severe inflammation on contact with the eyes or open cuts.
- It is a host for several fungal pathogens and insect pests.
After you read this, you will be able to:
- Identify Hairy Spurge (Euphorbia hirta).
- Know the its habitat.
- Know the best way to control this weed.
The distribution map is courtesy of The Atlas of Living Australia.
How to Identify Asthma Weed.
- Hairy Spurge is an annual weed with none to shot stems.
- It has a tap root, and a basal leaf rosette that is about 500 mm across.
- The taproot of Euphorbia hirta can be up to 60 cm long but it 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.
- As it grows, it sends out stolons, and then quickly spreads across the ground.
Category: This is a Broadleaf (Dicot) weed.
Photosynthetic Pathway: It is a C4 Weed.
Flower: Hairy Spurge flowers from the Spring to the Summer, with the flowers being in the upper leaf forks. The flowers have a green/yellow/creamy colour and they look like dense round flower clusters.
Height: It grows up to 40 cm high.
Leaf length: This 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 of Asthma Weed are 2 to 24 mm wide.
Reproduction:
- It reproduces by seed, and by its creeping stems that root at the stem joints.
- When the plants are 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 tends to germinate at temperatures of between 24°C and 29°C.
- However it can germinate at any time when the temperatures are over 16°C.
Populations can rapidly build up because:
- It germinates over a wide temperature range.
- It has a life cycle that takes only about 60 days from when it germinates to seed set.
Comments: Both the upper and lower leaf surfaces have a cover of close 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. You must remove all the roots, and dispose of them to avoid any re-growth.
- You must hand weed every 2 to 4 weeks. This is because of its fast growth rate, and the ability of this weed to quickly produce seed once it germinates.
- Due to its prostrate growth habit, mowing is not an effective way to manage Cat’s Hair.
- This weed thrives in thin or bare areas. This means that grass selection is important. You should consider factors such as shade, climate and the amount of use the area gets when you choose your turf grass.
Chemical Control of Asthma Weed:
Pre-Emergent Control.
There are currently two products with a label for this weed in Australia. These are BASF Freehand and Envu Esplanade.
- BASF Freehand only suppresses this weed.
- Envu Esplanade is for use around railroads, roads, industrial sites and utility corridors.
Overseas there are more options to choose from:
- Dithiopyr, Metalochlor, Pendimethalin, and Oxadiazon all suppress Cat’s Hair.
- Prodiamine has a label for its suppression, and long term control.
Post Emergents For Asthma Weed.
Most post emergents will control this weed, but the options in Australia are limited. We have personally had success with the use of ProForce Warhead Trio and saw results within 2 weeks.
Non Selectives For Asthma Weed.
- Glufosinate-ammonium provides control for 4 to 6 weeks. However, it then tends to grow back due to the limited movement of glufosinate.
- Glyphosate. If water quality is an issue then use ProForce Manta Ray.
The following are non-selective. They also have a long term residual, and stop any re-growth of this weed.
- Renegade. Renegade stops germination of this weed for up to 12 months. This reduces the need for several chemical 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. It then has a 3 month residual. It is also safe to use near trees.
Non Selectives For Asthma Weed.
Product | Active Ingredient | Group | Use Rate/Ha |
Glufosinate 200 | Glufosinate-ammonium | 10 | 1 to 6 L |
Rapid Fire 800 | Glyphosate | 9 | 0.9 to 1.35 Kg |
Numchuk Quad | Terbuthylazine + Glyphosate + Amitrole Oxyfluorfen | 5 + 9 + 34 + 14 | 20 to 25 L |
Cortex Duo | Nonanoic Acid + Oxyfluorfen | 14 | 7 L/1000L |
Renegade | Bromacil | 5 | 3.5 to 6.5 Kg |
