The cutting depth required to control calotrope (Calotropis procera) plants using mechanical techniques
Shane Campbell A C D , Laura Roden A B , Christopher O'Donnell A C and Melinda Perkins CA Tropical Weeds Research Centre, Biosecurity Queensland, Department of Agriculture and Fisheries, PO Box 976, Qld 4820, Australia.
B 694 Aremby Road, Bouldercombe, Qld 4702, Australia.
C The University of Queensland, Gatton Campus, Qld 4343, Australia.
D Corresponding author. Email: shane.campbell@uq.edu.au
The Rangeland Journal 42(2) 129-134 https://doi.org/10.1071/RJ20035
Submitted: 4 May 2020 Accepted: 15 June 2020 Published: 9 July 2020
Abstract
Calotrope (Calotropis procera (Aiton) W.T. Aiton) is an exotic woody weed that has invaded northern Australia’s rangelands since being introduced in the early 1900s. To expand the range of control options beyond herbicide-based methods, we undertook a stem/root cutting experiment that helped quantify the potential for using mechanical control techniques. Individual, medium-sized (1.72 ± 0.03 m high) calotrope plants were cut off at ground level (0 cm) or below ground (10 or 20 cm) using either a pruning saw or mattock respectively. All calotrope plants cut at ground level reshot vigorously. After four months they had more than twice the number of stems (7.4 ± 0.54) of the uncut control plants and by 12 months they were only 26 cm shorter than the control plants. In contrast, all plants cut at 10 or 20 cm below ground were killed. Some mortality also started occurring in the control and ground level (0 cm) treatments after eight months, but appeared to be associated with a dieback phenomenon. Nevertheless, the results demonstrate the potential to use equipment that severs the root system below ground, such as blade ploughs and cutter bars. A subsequent stick raking demonstration achieved moderate plant mortality (72%) after 13 months, yet produced a six-fold increase in original plant density as a result of new seedling emergence. This finding supports the view that mechanical disturbance will often promote seedling recruitment, and land managers need to have the capacity to undertake follow-up control practices to avoid exacerbating the problem.
Additional keywords: invasive species, rangeland management, rubber bush, woody weed.
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