Effects of herbicide and water availability on the bulbils of the invasive terrestrial plant Furcraea foetida

Abstract

Invasive terrestrial plant, Furcraea foetida (Mauritius hemp) originates from central and South America and is invasive in South Africa. The species predominantly reproduces asexually by producing copious bulbils that facilitate spread (especially down slopes). In this study, we investigated the efficacy of a herbicide (viz. fluroxypyr/ picloram), both in situ and ex situ, to control bulbils of F. foetida. Additionally, given the increasing evidence that suggests that climate change could alter the growth and physiology of invasive alien plant species, and hence their management, we also investigated bulbil responses to reduced water availability. For the in situ herbicide investigation, three study sites were selected along the coast of KwaZuluNatal (South Africa) and seventy herbicide-treated and seventy untreated bulbils (per site) were monitored. There was 0–13% bulbil survival in herbicide-treated bulbils compared to 100% survival in control bulbils in situ after four weeks. In bulbils that survived, the herbicide appeared to limit rooting, which might also limit recruitment. For the ex situ experiment, we planted herbicide-treated bulbils, that were subjected to different durations of herbicide exposure, in a shade house and found that all herbicide-treated bulbils died after 28 days. The irrigation experiment showed no negative physiological effects on root length, plant height, chlorophyll content and leaf area in bulbils subjected to a water deficit. However, it should be noted that the final biomass was significantly higher in water-deficit treated plants (2.83 g) compared to the normally irrigated plants (0.82 g) indicating that the species may be adapted to arid climates. This study found that [2.5%] fluroxypyr/picloram is effective against F. foetida bulbils, suggesting that chemical control by targeting the bulbils is a potential management option to minimise spread and invasiveness. The study also suggests that F. foetida has the potential to tolerate drought conditions in subtropical KwaZulu-Natal, which advocates for the prioritisation of managing populations in arid regions of South Africa.