Black Medic (Medicago lupulina)
Black Medic is also known as Yellow Trefoil. It is an aggressive, prostrate Summer annual, and forms a dense, mat-like cover across turf. It germinates in the late Spring, and then continues to grow through the heat of the Summer, before it diesoff once the weather cool down.
After you finish reading this, you will be able to:
- Identify Black Medic or Yellow Trefoil.
- Know what conditions favour Yellow Trefoil.
- Know the best cultural and chemical options to control Black medic or Yellow Trefoil.
Although not directly toxic to livestock, if they eat enough of it, Black Medic causes serious gastric issues.
it is often mistaken for White Clover or Yellow Wood Sorrel.
Differences between Black Medic and other Trifoliate Leaf Weeds.
Black medic and White Clover grow in similar sites and are often found growing together in turf. It is also mistaken for Creeping oxalis.
Spreading | Trifoliate | Leaf Shape | Tooth at Tip of Leaf | Toothed Leaf Margins | Annual/ Perennial | Soil Conditions | Habitat | Flowers | |
Black Medic | Yes | Yes | Oval serrated | Yes | Yes | Summer Annual | Low pH | Full sun | Yellow |
Creeping Oxalis | Yes | Yes | Heart shape | No | Smooth | Perennial | High pH | Shade | Yellow with 5 petals |
White Clover | Yes | Yes | Smooth rounded | No | Yes | Perennial | High pH | Open areas | White |
The distribution map is courtesy of The Atlas of Living Australia.
More information on common lawn weeds is in our weed ID chart. What they reveal about soil conditions is in our blog on indicator weeds.
How to Identify Black Medic.
Black medic is an indicator weed of low soil N in lawns as it outcompetes weak grass. Although classed as a cool season Summer annual, in mild Winters some plants may survive to act as perennials.
It spreads easily by seed and will form large colonies if left undisturbed. Black Medic is a low-growing weed and has three heart shaped trifoliate leaves.
It spreads up to 0.75 m prostrate across the ground.
Category: Broadleaf (Dicot).
Photosynthetic Pathway: C3 Weed.
Flower: Yellow Trefoil has single round yellow flowers or flowers in clusters of up to four.
Height: It grows up to 10 to 60 cm in height.
Leaf length: The leaves of medic are 12 to 18 mm long.
Leaf width: Leaf width is 3 to 10 mm wide.
Reproduction: Black Medic reproduces by seed. Immature plants flower within six weeks of emergence. It produces seeds throughout the growing season. and a single plant produces up to 6,600 seeds. These seeds remain viable in the soil for several years.
Comments:
- Coarse hairs cover the leaves, and the root system has a coarse branched taproot that may form nodules. These nodules add nitrogen to the soil.
- Black Medic has a symbiotic relationship with Rhizobium bacteria. These form root nodules, and fix atmospheric N.
- The leaves of Black Medic have shallow teeth towards their tips, and dark spots near their centre.
- Each leaflet has a small spur at its tip.
Habitat: This weed is a good indicator of soil problems. It thrives in drought, low N, well-drained, compact soils and bare areas. Black Medic is tolerant of a wide range of mowing heights. It is often found in disturbed areas or lawns, as well as in fields and pastures.
How to remove Black Medic from your lawn.
Cultural Control of Black Medic.
- Manage Black Medic through good turf management practices that encourage a dense stand of turf, and make it difficult for Black Medic to persist.
- Hand pull or use a weeding tool and make sure that you remove the large taproot.
- As it favours compact soils, soil aeration can also help manage this.
- Also, bare in mind that keeping N up to your turfgrass helps deter this weed.
- Black Medic does not grow well in shade so if you adopt practices that increase turf competition it will help to manage this weed. These include mowing at the right height for the turf species present and watering as and when required.
Chemical Control of Black Medic.
- ,Treatment is best in the late Spring to early Summer and in the early to late Autumn.
- The best time to apply post-emergent herbicides is as early in the season as this is when plants are small.
- You may need several applications to get the best results.
Pre-emergent Herbicides for Black Medic.
- The herbicide Dithiopyr provides some pre-emergent control in lawns but is not registered for this in Australia for this.
- Oxadiazon and Prodiamine do not work well to prevent this weed.
- Isoxaben (Gallery) is an excellent pre-emergent for Black Medic but has limited ares where it can be used.
Post Emergent Herbicides for Black Medic Control.
The most important factor to effectively control Black Medic is to apply post-emergent herbicides when the plants are small. Treatment is best over the entire area rather than spot treating.
There are several post-emergents for Black Medic:
- 2,4-D.
- Duke 100WG.
- ProForce Recondo.
- Contra M and Warhead Trio.
- Quinclorac. Not registered in Australia.
- Casper Herbicide is registered to control Burr Medic (Do not use Contra M and Casper on Buffalo grass).
Table of Black Medic Post Emergent Herbicide Rates.
Product | Active | Chemical Group | Rate/Ha | Comments | ||||
Casper | Prosulfuron + Dicamba | 2 and 4 | 800g-1Kg | Apply from Autumn to Spring. Use high rates in cool months or if high weed pressure. Control takes 4 to 6 weeks. Use an NIS at a rate of 0.25 to 0.5% v/v. | ||||
2,4-D | 2,4-D | 4 | 1.8-3.2 | Wet foliage thoroughly. DO NOT mow lawn for 1 week before and at least 1 weed after application. DO NOT use on Buffalo grass (WA only). | ||||
Duke | Iodosulfuron | 2 | 100g | Always use an NIS or Overtake Oil. Use in 200-500 L/ha water. | ||||
Recondo | Trifloxysulfuron | 2 | 225g | Use an NIS at 0.25% v/v (1000 g ai/L), 0.42% v/v (600 g ai/L) or Overtake Oil at 1%v/v. Ensure uniform placement onto leaves & into crowns. Water volume is 400 to 800 L/ha. You may need a repeat application in 4 to 6 weeks. Allow at least 6 weeks before overseeding. You may see discolouration on Qld Blue and Zoysia. | ||||
Warhead | MCPA + Clopyralid + Diflufenican | 4 + 12 | 5 L | You may see discolouration on kikuyu, carpet grass and Queensland blue. Avoid overlapping. Use an NIS. | ||||
Contra M. | Dicamba + MCPA | 4 | 6.5 L | Apply in 250-400L water. DO NOT use on Buffalo grass. After use do not mow for 2 days before or after application or fertilize within two weeks. | ||||
Non Selective Control of Black Medic.
You cannot use any of these on lawns or turf areas to selectively remove Black Medic.
- 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.
These are non-selective but also have a long term residual and stop any re-growth of Yellow Trefoil or Black Medic.
- Renegade. Renegade stops germination of Black Medic for up to 12 months. This reduces the need for multiple herbicide applications.
- Numchuk Quad. This gives post and pre emergent control of Yellow Trefoil for up to 12 months.
- Cortex Duo. Cortex Duo gives a rapid knockdown of Black Medic, and residual control for up to 3 months. It is also safe to use around trees.
