Determining the growth responses of Phyla canescens to shoot and root damage as a platform to better-informed weed-management decisions

Understanding the responses of invasive plants to control methods is important in developing effective management strategies. Lippia (Phyla canescens (Kunth) Greene : Verbenaceae) is an invasive, perennial, clonal forb for which few control options exist for use in the Australian natural and agro-ecosystems it threatens. To help inform management decisions, lippia's growth responses to damage it may experience during proposed control measures, i.e. cutting, crushing, twisting, were assessed in three glasshouse experiments using either whole plants or plant pieces. Plants quickly recovered from severe damage through growth from shoot and root buds at stem nodes. After shoot and root removal, the relative growth rate of the remaining plant was twice that of controls, suggesting tolerance to damage. Lacking buds, root pieces and isolated stem internodes were incapable of responding. Crushing and cutting individual ramets and plant pieces induced the largest responses, including release of axillary buds on damage or removal of apical buds, but full recovery was not achieved. Lippia will be difficult to control because of its ability to rapidly propagate from stem fragments possessing undamaged or damaged nodes; thus, the full impact of control methods that increase fragmentation (e. g. grazing) should be assessed before implementation. Our results also suggest that the most effective biological agents will be those that limit lippia's vegetative growth and spread, such as shoot-or crown-feeding insects.