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Oxalis-Horned

HORNED OXALIS

Oxalis corniculata
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Oxalis-Horned

DESCRIPTION

This species of oxalis is the larger one and is the one of more concern. The other smaller, common relative that looks similar is creeping oxalis (Oxalis exilis), which is a native oxalis.

Horned oxalis is a perennial weed species that grows low to the ground.

The flowers are yellow, and grow up to about 1cm in diameter, sometimes singly, but more often in clusters of from two up to five flowers per stalk. It flowers from December to January in most locations.

Leaves are trifoliate, which means they are made up of three leaflets each of which is notched on the outer end. This forms the classic ‘three-leafed-clover’ shape. The leaves are generally up to 20mm across.

The similar native creeping oxalis mentioned above also has yellow flowers and trifoliate leaves but it’s smaller in all respects (e.g. the flowers are normally only up to 10mm across). The creeping oxalis flowers are also smaller, and nearly always appear only singly rather than in clusters.

Horned oxalis spreads readily because of its stolon's, which is a stem that creeps along the ground and produces new roots at the stem nodes. This allows the plant to form quite dense patches in pastures, turf and lawns. The plant also spreads via seeds, but does not have the underground bulbs found on some other similar species (e.g. fishtail oxalis, Bermuda buttercup, pink shamrock and others)

There have been reports from Australia of sheep being poisoned by horned oxalis, though nothing similar reported in New Zealand.

HABITAT

Horned oxalis is found across most of the world, and is common throughout New Zealand. It particularly favours gardens as well as closely grazed pastures. It also appears in lawns, ornamental and sporting turf, though the smaller, native creeping oxalis is more common in those locations in NZ. 

HERBICIDES TO CONTROL OXALIS

Horned oxalis, like most of the oxalis species, is able to tolerate most of the commonly used selective herbicides, and results with common sprays like Rainbow & Brown MCPA750 and WHACK – 2,4-D 800 can be very disappointing, as can treatment with sprays containing clopyralid.

The one well-proven herbicide active ingredient is triclopyr, whether alone or in combination with picloram.  However the products containing picloram as well as the triclopyr (e.g. GrassMate) will cause severe clover damage, whereas those containing triclopyr alone are far less damaging to clover, especially at the moderate application rates required as follows:

Spot Spraying Herbicides to Kill Oxalis
  • TRICLO Herbicide – 2ml/10m2
  • LawnMate – 12ml/1L water will suppress oxalis but is is unlikely to completely eliminate it. You may need to apply multiple times over a season to weaken the plant. NOT APPROVED FO USE ON PASTURE OR CROPLAND.
Boom Spray Herbicides

In all cases when spraying, for best results add SprayWetter  penetrant at 10ml/10L water to ensure thorough penetration of the herbicide into the plant.