The impact of gorse thrips, ryegrass competition, and simulated grazing on gorse seedling performance in a controlled environment

Biological control agents of weeds are often used in conjunction with other management practices to reduce the negative impacts of invasive weeds. When assessed in a factorial glasshouse experiment, a combination of gorse thrips, ryegrass competition, and simulated grazing (manual clipping) resulted in a gorse seedling mortality of 93% compared to no mortality in the untreated control. Mortality was 23 and 33% when ryegrass competition was combined with one additional factor of either thrips or grazing, respectively. Individual factors and the combination of gorse thrips and grazing did not cause any seedling mortality. The shoot dry weight of gorse seedlings was reduced by ryegrass competition (96%), simulated grazing (74%), and gorse thrips (57%). The root dry weight of gorse seedlings was also reduced by simulated grazing (70%) and gorse thrips (60%) but the effect of ryegrass competition was not measured. The interactions between treatments and the role of multiple control tactics within an integrated weed management program are discussed.