Asthma Weed (Euphorbia hirta)
Asthma Weed is also known as Hairy Spurge or Cat’s Hair. Hairy Spurge is an annual soft leaf plant, that produces a few spreading to upright reddish stems that are up to 40 cm tall. Its stems have a cover of yellow hairs and contain a milky sap.
After you read this, you will be able to:
- Identify Asthma Weed and Hairy Spurge.
- Know the habitat of Hairy Spurge or Cats Hair.
- Know the best cultural and chemical options to control Cat’s Hair.
The sap is toxic if ingested, and causes photosensitive skin reactions and severe inflammation on contact with eyes or open cuts.
You often find Asthma Weed in turf or in plant beds. However, you can also find it growing in sidewalk cracks and between pavers.
Being a semi-tropical and tropical warm season weed, Hairy Spurge does not tolerate frosts, and prefers warm and sunny locations. However, it will also grow in dense shade.
Asthma Weed has its name because it treats asthma and several lung diseases. This plant is effective against several diseases, such as 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.
Asthma Weed or 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 wide. As it grows, it sends out stolons, and quickly spreads across the ground.
The taproot of Asthma Weed is up to 60 cm long but is usually 15 to 20 cm long. The rest of the root is made up of secondary fibrous roots that grow off the main taproot.
Category: Broadleaf (Dicot).
Photosynthetic Pathway: Asthma Weed is a C4 Weed.
Flower: Hairy Spurge flowers from Spring to Summer. The flowers are in the upper leaf forks, and the green/yellow/creamy coloured flowers 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 creeping stems that root at the stem joints. When the seed pods mature they explode to disperse the seeds.
A mature plant produces several thousand seeds over the course of just 8 to 10 weeks. Hairy Spurge germinates best at temperatures between 24°C and 29°C, but germination occurs at any time when the temperatures are over 16°C.
Its wide rage of germination temperatures, coupled with a life cycle that takes only about 60 days from germination to seed set, means an Asthma Weed populations can rapidly build up.
Comments: Both the upper and lower leaf surfaces have a cover of close-lying hairs. As the plant matures it loses the upper leaf hairs.
Habitat: Hairy Spurge is a weed of verges, footpaths, lawns, bare areas, and playing 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 in your lawn.
You can control Cat’s Hair by cultural and chemical means.
Cultural Control of Asthma Weed:
- Hand weeding is effective but you must remove all the roots of Asthma Weed, and dispose of them to avoid re-growth. This must be done regularly (every 2 to 4 weeks) because of this plants fast growth rate, and its ability to quickly produce seeds once it germinates.
- Due to its low prostrate growth habit, mowing is not an effective management tool for Asthma Weed.
- Asthma Weed thrives in thin or bare areas so grass selection is important. Factors such as shade, have an important role in this, as to does the climate and the amount of wear.
Chemical Control of Asthma Weed:
Pre-Emergent Control of Asthma Weed.
There are currently two options for products with a Hairy Spurge or Asthma Weed registration in Australia. These are BASF Freehand and Envu Esplanade.
- BASF Freehand only suppresses this weed as a Pre-emergent herbicide.
- Envu Esplanade is a pre-emergent herbicide 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 Asthma Weed.
- Prodiamine has a label for suppression and long term control.
Post Emergent Control of Asthma Weed.
Most broadleaf herbicides will control this weed, although registered 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, but it 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 re-growth of Asthma Weed.
- 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 Asthma Weed, and residual control for up to 3 months. It is also safe to use around trees.
