Residual herbicide treatments reduce Andropogon gayanus (Gamba Grass) recruitment for mine site restoration in northern Australia

Abstract

Summary Weed invasion is a major threat to Australian tropical savannas, and controlling weeds is essential for successful re‐establishment of native species on disturbed sites. Gamba Grass (Andropogon gayanus) is an African grass which has invaded large areas of tropical savanna across northern Australia. Current management strategies in northern Australia focus on fire and glyphosate to effectively control mature plants; however, re‐establishment of infestations from the soil seed bank remains a major challenge to eradication efforts. This study focused on the effects of soil seed bank treatments on Gamba Grass recruitment on a mine site in northern Australia. Adult Gamba Grass plants within test plots were killed with glyphosate to exclude resource competition. Chemical, physical and biological treatments were then applied, and the treatment effects on subsequent Gamba Grass seedling emergence and survival quantified. Seedling emergence was significantly reduced by three of the four residual herbicide treatments tested. The most effective herbicide treatments, dalapon and sulfometuron, reduced emergence by 90% compared to the standard glyphosate treatment alone. This equated to a reduction in Gamba Grass seedling emergence from 1 seedling/m2 to 1 seedling 10 m−2, a major improvement for Gamba Grass management. These residual herbicide treatments significantly reduced the population density of Gamba Grass for at least 5 months after emergence. The physical and biological treatments did not have a significant effect on seedling emergence. This significant reduction in Gamba Grass seedling emergence and survival can substantially improve Gamba Grass management. Reducing re‐colonisation from the soil seed bank using residual herbicides provides a valuable management tool for land managers, integrating readily with established strategies for controlling the mature plants.

Do Weeds Hinder the Establishment of Native Plants on a Reclaimed North American Boreal Mine Site?

“…Weed invasion on mine sites post-reclamation is an ongoing management issue worldwide, particularly if weeds dominate to the point of altering the desired plant community. For example, the introduced forb Tripleurospermum perforatum (scentless chamomile) is establishing and dominating on reclaimed well sites in Alberta [1,2], Andropogon gayanus (Gamba grass) is invading reclaimed mine sites in northern Australia [3], and the encroachment of a non-native shrub, Elaeagnus umbellate, is dominating coal mining reclamation sites across the eastern United States [4]. These species, and many others around the world [5,6], inhibit revegetation of desirable species post-disturbance and are considered detrimental to the reclamation goal of a native plant community.…”