Kudzu (Pueraria montana var. lobata) is an invasive plant and the target of a classical biological control program in the United States. Experiments using simulated herbivore damage were undertaken to study how kudzu might respond to biomass removal by potential biocontrol agents, including defoliators, shoot-clippers, and root borers.
Results/Conclusions
In a two-year study on established field plants, 75% leaf removal significantly decreased internode distance and increased the total number of stem nodes compared to 50% leaf clipping, 50 and 75% shoot clipping, drilling one or two 10-cm holes into root crowns, and no damage. Results from a second field site were less clear, and observations suggested that light exposure may influence plant response to herbivory. A greenhouse study comparing three light treatments (0, 60, and 100% direct light) and two damage treatments (weekly 50% leaf removal and no damage) was conducted to address this issue. There was no difference in aboveground biomass production for plants grown in 100% light, but plants in 60% light with 50% leaf removal and plants in 0% direct light produced significantly less biomass than plants in 100% light. A two-year experiment conducted in an open agricultural field exposed plants to full light, and treatments (50 and 75% leaf and shoot clipping, and control) were applied to transplanted greenhouse-grown plants once a week for 8 weeks. In 2008, leaf clipping (50 and 75%) and 75% shoot clipping reduced biomass production; leaf clipping decreased internode distance; and 75% leaf clipping decreased the total combined length of vines per plant. In 2009, plants produced less aboveground biomass, root biomass, and smaller internode distances when subject to 50 and 75% leaf clipping. Of the damage types investigated, leaf damage proved capable of suppressing kudzu growth, while shoot clipping had less of an effect. Suppression is expected to vary with light exposure, and further analysis is required to determine if plant survival was influenced by the amount of light received. The preliminary results of this work suggest that evaluation of potential biocontrol agents should focus on host-specific defoliators, and that planting trees to increase shade in areas invaded by kudzu may enhance biological control.