Evaluating management strategies for aphid-transmitted yellow dwarf viruses in perennial ryegrass seed production

Epidemiology and management of aphid-transmitted yellow dwarf viruses (YDVs) have received international attention in small grain crops over the past century. However, focused research regarding YDV management in grass seed production systems, including perennial ryegrass (Lolium perenne L.), is limited. An integrated pest management program is needed to reduce the impact of the aphid-YDV complex in perennial grass seed crops. The objectives of the study were to evaluate the effects of nitrogen fertilizer rate, and the timing and frequency of foliar insecticide applications on aphid abundance, YDV disease incidence, and seed yield in two perennial ryegrass cultivars in small-plot field trials from 2021 to 2024. Trade-offs in economic returns across treatment combinations and YDV detection using remote sensing were also observed. Aphid and natural predator densities varied across foliar insecticide treatments. The high nitrogen rate increased YDV incidence across three field seasons in both cultivars. Seed yield and economic returns were greatest for the less susceptible cultivar when fully protected with one insecticide treatment per season (autumn, spring, and summer). A higher than recommended nitrogen rate did not increase seed yield across treatment combinations in first-year stands; however, an increase was observed in second and third-year stands when YDV infection averaged >50%. Selecting resistant cultivars and reducing aphid populations during the autumn and spring aphid flights is critical for maximizing seed yield potential in perennial ryegrass. Furthermore, a lower nitrogen rate can be used in first-year stands to save input costs with no impact on seed yield potential.