Tall-growing (up to 2.5 m tall when growing in maize) annual herb
Two growth forms, either erect and single stemmed, or very branched and spreading, depending on whether it is growing in competition or in the open
Leaves are dark green, sometimes mottled purple and similar in shape to grape leaves
Stems have short coarse hairs and may be covered with purple blotches
Flowers are inconspicuous in the leaf axils
Fruit are woody burs that  are covered in hooked spines which can attach to livestock wool or hair and clothing
Each bur contains two seeds and each plant can produce many hundreds of burs
Burs are commonly dispersed by livestock, people, farm equipment, in seed or feed, in gravel or soil and by water movement
Burs have air pockets around the spines which allow them to float and be spread in water.
Biology
Origin
Originally from North America
In Australia, first recorded at Noogoora station in Queensland (hence the name ‘Noogoora bur’).
Ecology
Prevalent in temperate regions, usually in fertile soils, occurring as a weed of cultivation, cropping and along roadsides
A relatively new weed to New Zealand, found on cropping properties in the Waikato and Bay of Plenty. It could become a major problem in both crops and pasture if allowed to spread
Often found close to water courses and areas where soil has been disturbed on previously infested land
Seeds germinate mainly in late spring, with ongoing germination occurring in summer
Generally grows in summer, up to 1.5 m high or up to 2.5 m in maize
Flowering is triggered by day length and occurs after the longest day of the year (January to March)
After producing seeds, the plant dies off in autumn. Although dead, it can remain standing and carry its burs for many months
Late germinating or shaded plants produce burs very quickly when they are still quite small, sometimes when only a few centimetres tall
Each bur contains two long thin seeds. Both seed can germinate simultaneously but more often only one seed germinates. When this happens the second seed usually decays or occasionally persists until the next season
The plant contains chemicals that can impede the growth and germination of neighbouring plants (allelochemicals).
Dispersal
Burs are covered in hooked spines which can attach to livestock and clothing
Burs are commonly dispersed by livestock, people, farm equipment, in seed or feed, and in gravel or soil or in moving water
Burs have air pockets around the spines which assist in dispersal by water as it enables them to float. Because of this Noogoora bur can be widespread and abundant near waterways, or after spring and summer floods.
Impacts
The large seed germinates into a fast growing and highly competitive weed that can cause significant losses in many crops
Seeds are poisonous to stock, particularly pigs and cattle
The fruit (small woody ‘burs’) easily entangle in sheep’s wool and decrease fleece quality
Plants can compete with pasture species and carry fungal diseases capable of infecting horticultural plants
Noogoora bur has been targeted for eradication by several Regional Councils including Waikato and Bay of Plenty. As such it is illegal to propagate and knowingly spread this plant and all sightings must be reported to the respective councils.
Control
Noogoora bur is moderately to highly susceptible to most pre and post-emergence herbicides used for control of broadleaf weeds in maize. The difficulty in managing this weed is due to its ability to continue germinating throughout the summer months
In pasture plants can be controlled by hand pulling or spot treating with Tordon Pasture Boss (aminopyralid + triclopyr or Tordon 2G prills (picloram).
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