Khaki weed is a summer-growing, mat forming perennial (long lived) herb that produces numerous spiny burrs and is a problematic weed in recreational reserves.
Description
Khaki weed (Alternanthera pungens) is a creeping herb that forms a dense mat with a perennial woody taproot (main root) and annual above-ground growth.
The lateral stems are reddish with soft, silky hairs. The stems grow up to 60 cm long and can develop roots where stem nodes touch the soil.
The leaves are numerous and grow in opposite pairs of unequal size up to 4 cm long. The oval shaped leaves are green with short stalks and are sparsely haired.
Flowers are inconspicuous and appear mainly in summer and autumn. They occur in clusters in the axils of the leaves and are surrounded by sharply-pointed, chaff- coloured bracts.
The fruit is a prickly, chaff-coloured burr about 1 cm long. Mature plants can produce hundreds of burr covered seeds which can remain viable for many years.
Seeds germinate in the spring but can also germinate in response to summer rain. New growth from seed and established tap roots, develops over spring and summer. All above-ground growth dies off over autumn with plants going dormant through winter.
Impacts
Khaki weed is most problematic in recreational and lawned areas, as the spiny burrs readily penetrate skin and can cause injury to feet of humans and animals.
Khaki weed also impacts on irrigated pastures and production systems. It competes well and benefits from summer moisture. Burrs degrade wool quality and if inadvertently eaten, the spiny burrs can damage the mouths of stock.
Distribution
Khaki weed is native to Central and South America.
It prefers light soils, warm conditions and high soil moisture over spring and summer.
In the the Adelaide area, khaki weed is found predominantly across the urban environment on road verges, footpaths, in reserves with grassed areas and in private gardens. Plants may also be found in caravan parks, camp sites and picnic areas.
Seed-burrs spread easily by attaching to feet, footwear, tyres, clothing and fleece and are easily transported with mowing equipment and machinery.
Management
Khaki weed is a declared and notifiable weed under the Landscape South Australia Act 2019. The sale of khaki weed or contaminated goods; and its movement on a public road are prohibited. It is the responsibility of the land owner to destroy and control these plants on their property. Infestations must be reported to the regional Landscape Board.
We require the destruction of all plants and can assist landholders with the appropriate removal of identified plants.
Control methods
A long-term control program is required to control khaki weed because of the abundant and persistent seeds and robust taproot. An effective control strategy will include both mechanical and chemical control.
Survey for plants throughout spring to early autumn, to control any germination in response to summer rain.
Hand pulling
For a small number of plants and in areas of lawn, hand hoeing and hand pulling (with gloves) can be effective if the crown and the taproot is removed.
Cultivation
Used in pasture areas or irrigated horticulture, turning soil over to a depth of at least 15 cm with farm machinery can be useful for treatment of seedlings and regrowth. Cultivation can also spread seed so best to cultivate before seed set and clean equipment before moving to uninfested areas.
Chemical
Herbicides should be applied when the weeds are actively growing and before seed set. Control treatments must be applied annually and persistently throughout the growing season until the infestation is eradicated.
For advice on chemical options please refer to Controlling declared weeds in SA.
Main banner image courtesy of Harry Rose, WikiMedia Commons.
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