Form: herbaceous — annual
Status: present in WA
Yellow burr weed (Amsinckia spp.) is native to North and South America. Yellow burr weed grows vigorously on a wide range of soil types, including sandy surfaced mallee soils, black clays and red loams. The three species of Amsinckia are declared plants throughout WA. Their features are similar so for practical purposes they can be treated as one weed.
Yellow burr weed is an erect herb reproducing only from seeds. It germinates over an extended period in the autumn and winter, making it very difficult to control by cultivation.
Stems: Bristly erect stems up to 70 centimetres high.
Leaves: Dark green to grey-green true leaves, with fleshy prominent midribs and rough surfaces. The rosette leaves are oval up to 15 centimetres long by four centimetres wide while the leaves of the flowering stems are narrower. Leaves are sessile (stalkless) and arranged alternately on the stem. All leaves are covered with short stiff hairs and feel rough to the touch. It has Y-shaped cotyledons (seed leaves).
Flowers: The small flowers are yellow to orange, and numerous. They are formed on one side of a 10-15 centimetres curved spike at the ends of the branches.
Seeds: Four hard rough angular seeds about 2.5 millimetres long, surrounded by a husk covered with stiff bristles are formed on each flower. The seeds fall to the ground when ripe.
Agriculture and economic impact
Yellow burr weed is a major weed of cereals in northwest United States, the Wimmera and Mallee districts of Victoria and in New South Wales. Isolated infestations have been found occasionally in the cereal growing areas of WA.
Yellow burr weed competes vigorously with cereals for light and nutrients, mainly nitrogen, having a serious impact on yields.
The plant contains poisonous alkaloids which cause liver damage. Pigs, cattle and horses have been poisoned by eating contaminated seed; however, sheep and poultry are relatively resistant.
Declared pest category
The Western Australian Organism List (WAOL) contains information on the area(s) in which this pest is declared and the control and keeping categories to which it has been assigned in Western Australia (WA). Search for yellow burr weed in the WAOL us.ing the scientific name Amsinckia
Requirements for land owners/occupiers and other persons
Requirements for land owners/occupiers and other persons if this pest is found can be sourced through the declared plant requirements link.
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Pest and Disease Information Service (PaDIS)
Yellow burr weed is resistant to control by the phenoxy (hormone) herbicides. Control methods for this declared plant can be found through the yellow burr weed control link.