Learning from Past Attempts: Does Classical Biological Control of Noogoora Burr (Asteraceae: Xanthium occidentale) Have a Promising Future?

Abstract

Noogoora burr (Asteraceae: Xanthium occidentale) is an annual from the Neotropics that is a serious weed of rangeland and agricultural regions in many parts of the world. It was one of the first weeds to be systematically targeted for biological control and there were two major phases in the Australian program; 1929-1940, and 1953-1975. Past attempts at biological control are reviewed to identify opportunities for renewed efforts, and for its historical value. Only one insect species was released in the first phase, but host-specificity restrictions were loosened during the second phase resulting in the release of two other insect species. None have been effective. A fourth agent, released primarily for parthenium weed, has had limited impact. However, the rust, Puccinia xanthii, was accidentally introduced in 1975. It has resulted in complete control of Noogoora burr in much of eastern Australia, but has had little or no impact in far northern Australia. Past failures, judged through hindsight, can be attributed to a failure to identify the full native range, lack of consideration for pathogens prior to 1975, and poor understanding of plant compensatory mechanisms and other challenges that an agent must overcome to be effective. A renewed effort specifically targeting Noogoora burr in far northern Australia holds considerable promise. It should include surveys for new agents within the native range of the Xanthium complex, and a systematic search for isolates of the P. xanthii rust that are climatically adapted to tropical conditions in Australia.