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Knowledge of the spatial distribution of weed infestations over regional scales is essential for effective management of source populations and to assess future threats. To this end, the distributions of Nassella trichotoma across a study area in south-east New South Wales, Australia, were analysed using the geographically local Getis-Ord G(i)* spatial hotspot clustering statistic. The clustering of N. trichotoma observations was analysed at three infestation levels: presence (at any density), patch level and the occasional plant level. The results indicate that there are c. 578 km(2) of cells containing N. trichotoma in strongly clustered infestations, 11.2 km(2) within weakly clustered infestations distinct from the main clusters, and 55 km(2) that are not clustered. There are 117 km(2) of strongly clustered patch level cells, 3 km(2) in distinct but weak clusters, and none outside of a cluster area. Of the occasional plant level cells, 329 km(2) are strongly clustered, 6.2 km(2) are in distinct but weak clusters, and 19 km(2) are not clustered. These results provide a mechanism by which control efforts can be prioritized. The analysis approach described in this paper provides a consistent, quantitative and repeatable approach to assess weed infestations across regional scales and can be applied to any weed species for which spatial distribution data are available.