Lesser Swinecress (Lepidium didymum)
Lesser Swinecress is known as Hogweed or Annual Ragweed, and is a spreading or semi-erect annual to perennial. It is a member of the Brassica family and so is in the same family as cabbage, kale, and broccoli.
Swinecress tolerates heavy traffic, close mowing, and grows aggressively in turf areas with little competition.
Swinecress, sometimes germinates in the Spring but mainly in the Autumn. It then grows rapidly, and forms a rosette that is up to 200 mm in diameter. As it matures the leaves become more lobed and then pinnate. Lesser Swincress has a distinctive foul cress smell when you crush it.
The leaves of this plant are edible, and have a salty, cress or mustard flavour.
The distribution map for Lesser Swinecress is courtesy of The Atlas of Living Australia.
After you read this, you will be able to:
- Identify Lesser Swinecress or Hogweed.
- Know the habitat of Lesser Swinecress.
- Know the best cultural and chemical options to control Lesser Swinecress.
How to Identify Lesser Swinecress.
When young, Swinecress is easily confused with Bindii, and Common Cotula or Carrot weed.
Category: Broadleaf (Dicot).
Photosynthetic Pathway: C3 Weed.
Flower: Swinecress flowers bloom from February through to October. It has tiny, white, four-petaled flowers on stalks that cluster along the flowering stem. These form a flower head that is about 1 to 4 cm long. The flowering stems mostly arise from where the leaf stalk meets the main stem.
Height: Young Swinecress plants exist as rosettes until it matures and a stem develops.
Lesser Swinecress grows in a prostrate or low-growing fashion. The stems spread to almost 0.5 m along the ground but their tips tend to rise. The lower leaves grow on short stalks, whilst the upper leaves are stalkless and are alternate to one another along the stem.
Leaf length: The leaves are deeply lobed cut, but are not fully divided into leaflets (compound). They are about 1.5 to 7 cm long.
Leaf width: The leaves can be hairy or hairless, and are 4 to 12 mm wide.
Reproduction: Lesser Swinecress spreads only by seed.
Comments: The leaves become increasingly lobed and ultimately pinnate as the plant matures. As Swinecress matures, the prostrate stems form extensive mats on the ground if left alone. These look the same as Wireweed from a distance.
Habitat: You find Swinecress in gardens, turf, along roadsides, and in disturbed areas. It tends to prefers higher rainfall areas.
For more information on weeds check out our weed ID Chart.
How to Control Lesser Swinecress.
You control Lesser Swinecress by cultural and chemical means, but successful management of this weed is best if you adopt an integrated approach.
Cultural Control of Swinecress:
Lesser Swinecress doesn’t like competition so if you maintain a dense turf cover it prevents it from getting a toe-hold.
Manual removal is effective but must be done at least every 8 to 10 weeks. Once the seed pods form, the seed often matures even if you uproot the plant. This means that you should aim to remove all plants offsite that are in flower, rather than leave them on the ground. This ensures that no viable seed remains.
Any soil disturbance often leads to a flush of seedlings.
It is tolerant of mowing in young lawns, but you can control it with selective turf herbicides.
Chemical Control of Lesser Swinecress:
The key to control this weed is to reduce the seedbank and keep it at a low level.
Pre-Emergent Control of Swinecress.
On this basis the pre-emergent herbicide BASF Freehand is worth looking at. This is registered to control Lepidium spp.
In the USA work shows that Isoxaben is especially good for to prevent Swinecress.
Post Emergent Control of Swinecress.
Once it gets a bit larger, you need to use MCPA. However, even this doesn’t work well once Swinecress gets more mature, so it is best to treat it while it is young. Other options include 2,4-D and Dicamba.
Work in India has shown that Topremezone (BASF Pylex Herbicide) gives excellent post emergent control of Swinecress in Chickpeas.
- 2,4-D. This tends to burn the top of White clover but it then grows back.
- MCPA.
- Warhead Trio. Safe on Buffalo grass.
- Contra M herbicide. Don’t use Contra M on Buffalo grass.
- Weed Blast MA. Safe on Buffalo grass.
- Dicamba. Don’t use Dicamba on Buffalo grass.
- Pylex Herbicide. Do not use on warm season turf.
- Stature. Stature Turf Herbicide is safe on all established cool and warm season grasses. Not for home garden use. A non-ionic surfactant is recommended.
Non Selective Control of Wireweed.
- 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 you use Glyphosate, and 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 Swinecress.
- Renegade. Renegade stops germination for up to 12 months, and reduces the need for multiple herbicide applications.
- Numchuk Quad. This gives effective post and pre emergent Swinecress control for up to 12 months.
- Cortex Duo. Cortex Duo gives a rapid knockdown of Swinecress, and residual control for up to 3 months. It is also safe to use around trees.
