What Is Mustard Weed?
Mustard Weed can grow upright as it matures, reaching heights of up to 80cm in Australian pastures and roadsides. In home lawns, it typically appears as a smaller plant with a basal rosette of jagged, deeply lobed leaves and purple-tinged stems. As it develops, it produces bright yellow flowers.
Crushing or disturbing the leaves releases a distinct mustard-like aroma. Because it spreads rapidly through its seeds, the most effective control method is a selective post-emergent herbicide, followed by a pre-emergent program to prevent future germination.
Mustard Weed thrives throughout temperate regions of Australia—particularly Victoria, New South Wales, South Australia, and southern Western Australia. It often invades lawns that are thin, stressed, or poorly maintained, and it can affect all popular warm-season grasses including Buffalo, Couch, Bermuda, Kikuyu, and Zoysia.
Most growth occurs in autumn and winter as soil temperatures cool. The weed matures quickly and can produce thousands of seeds by early spring. These seeds spread easily when the plant is disturbed and can remain viable in the soil for several years, making long-term management essential.
The best time to remove Mustard Weed is early—before it flowers and sets seed. For small, manageable outbreaks, hand pulling works well when the soil is moist. Ensure the entire taproot is removed.
Regular mowing before flowering can help reduce seed production, though it won’t eradicate existing plants.
For widespread infestations or mature plants, selective herbicides are commonly used. Products containing Dicamba and MCPA, such as Contra M Duo, are registered for controlling Mustards but are not safe for Buffalo lawns.
To maximise effectiveness, apply herbicides with a surfactant such as Wetter 600 to help the product adhere to the leaves.
For stubborn or isolated weeds, a non-selective herbicide like PCT Glyphosate 360 can be applied carefully. Because it kills any plant it touches, avoid blanket spraying—spot-treating with a sponge or brush is a safer option.
Always follow manufacturer directions regarding protective equipment and re-entry periods. Apply on dry, low-wind days to avoid drift onto healthy turf.
Options like vinegar or boiling water may scorch the foliage but rarely penetrate the taproot or affect the seed bank. As a result, regrowth is common within weeks.
Preventing Mustard Weed from reappearing starts with a quality pre-emergent herbicide. Pre-emergents form a barrier in the soil that prevents weed seeds from germinating.
Products containing Prodiamine (e.g., Spartan liquid, Onset GR granules) or Oxadiazon (e.g., Echelon Duo, Oxafert) can provide up to six months of protection against a wide range of invasive weeds.
Using pre-emergents not only reduces the need for repeated treatments but also helps maintain a denser, healthier lawn that’s more resistant to future weed invasions.
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