Integrated management of Harrisia cactus - the importance of understanding every tool in the box

Abstract

Harrisia cactus has been an ongoing concern since its recognition for negatively impacting grazing and natural areas in the Brigalow Belt Bioregion of Queensland during the 1950s. Initial attempts to control the weed using chemicals such as arsenic pentoxide proved to be hazardous, expensive, and ultimately ineffective. In the early 1970s, a search for biological control agents was conducted in Argentina, leading to the release of four insects in Queensland. By the 1990s, two of these insects had successfully established themselves and eradicated most Harrisia at the release locations within dense infestations in central Queensland. This success was largely attributed to the Harrisia mealy bug (Hypogeococcus pungens), with assistance from a stem-boring beetle (Nealcidion cereicola). However, recent surveys indicate the persistence of numerous dense, localized Harrisia cactus infestations throughout central Queensland, which are expanding despite the presence of the mealy bug. Similarly, although the biocontrol agent is well-established in the southern Brigalow Belt, the density and spread of the weed is increasing. Local councils and landowners across the state invest substantial amounts of money in the chemical control of Harrisia cactus. Nevertheless, it is widely recognized that while this method effectively kills above-ground plant parts, large established plants can regenerate from underground tubers, necessitating continuous monitoring for regrowth and ongoing chemical application. There are clearly limitations to current best practice management of Harrisia cactus and alternative methods should be explored before the situation deteriorates further. In the last four years, we have probed the limitations of relying solely on biocontrol or chemical control and explored alternative management methods, such as livestock grazing, controlled burning, and the management of invasive animal seed dispersers. Our research highlights the importance of understanding the strengths and weakness of each potential method, being flexible in their application, monitoring results and changing tactics when required.