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

Authors: Dorman, Seth; Rivedal, Hannah; ANDERSON, NICOLE - Oregon State University; MALISZEWSKI, DAVID - Oregon State University; Temple, Todd

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/14/2025
Publication Date: 4/16/2025
Citation: Dorman, S.J., Rivedal, H.M., Anderson, N.P., Maliszewski, D., Temple, T.N. 2025. Evaluating management strategies for aphid-vectored yellow dwarf viruses in perennial ryegrass seed production. Plant Disease. https://doi.org/10.1094/PDIS-12-24-2655-RE.
DOI: https://doi.org/10.1094/PDIS-12-24-2655-RE

Interpretive Summary: Management of aphid-vectored yellow dwarf viruses (YDVs) has received significant international attention in small grain crops. However, focused research regarding disease management in perennial grass seed production systems, including perennial ryegrass, is limited. Outbreaks of YDVs in perennial ryegrass seed crops in Willamette Valley, Oregon, the leading producer of cool-season grass seed worldwide, have been attributed to significant reductions in seed yield and stand longevity. An integrated pest management program is needed to reduce the impact of aphid-vectored YDVs in perennial ryegrass seed production. The study's objectives were to evaluate the effects of cultivar selection, nitrogen fertilizer rate, and the timing and frequency of foliar insecticide applications on aphid abundance, YDV disease incidence, and seed yield. Trade-offs in economic returns across treatment combinations and treatment effects on natural predator populations were also observed. A small-plot field trial of perennial ryegrass grown for seed was established in Corvallis, Oregon, from 2021 to 2022. Treatments included two cultivars ('Fastball' and 'Top Gun II'), two nitrogen rates (low and high application rates), and five foliar insecticide timing applications (untreated control and applications in the 'fall,’ 'spring,’ 'fall + spring,' and 'fall + spring + summer'). Flight activity of winged aphid vectors was predicted by ordinal date in the fall and spring. Aphid and natural predator populations varied across foliar insecticide treatments. Cultivar selection and a high nitrogen rate increased YDV disease incidence across two field seasons. Yield reductions were pronounced in the second year. Seed yield and economic returns were greatest for the less susceptible cultivar when fully protected with 'fall + spring + summer' insecticide treatments. A high nitrogen rate did not increase seed yield across treatment combinations in a first-year stand, although a significant increase in seed yield was observed in the second year when YDV infection averaged >50%. Selecting resistant cultivars and reducing aphid populations during the fall and spring flights is critical for maximizing seed yield potential in perennial ryegrass grown for seed. Continued research on host-plant-resistant cultivars in perennial grass seed crops is needed. Our findings are the first to provide management strategies for controlling YDV disease in perennial grass crops grown for seed and will inform ongoing research on host plant resistance in this production system.

Technical Abstract: Epidemiology and management of aphid-vectored yellow dwarf viruses (YDVs) have received significant international attention in small grain crops over the past century. However, focused research regarding disease management in perennial grass seed production systems, including perennial ryegrass, is limited. Outbreaks of YDVs in perennial ryegrass seed crops in the Willamette Valley, Oregon, the leading producer of cool-season grass seed worldwide, have been associated with significant reductions in seed yield and stand longevity. An integrated pest management program is needed to reduce the impact of the aphid-YDV virus vector complex in perennial ryegrass seed production. The objectives of the study were to evaluate the effects of cultivar selection, nitrogen fertilizer rate, and the timing and frequency of foliar insecticide applications on aphid abundance, YDV disease incidence, and seed yield. Trade-offs in economic returns across treatment combinations and treatment effects on natural predator populations were also observed. A small-plot field trial of perennial ryegrass (Lolium perenne L.) grown for seed was established in Corvallis, Oregon, from 2021 to 2023. Treatments included two cultivars ('Fastball' and 'Top Gun II'), two nitrogen rates (134.5 and 224 kg ha-1), and five foliar insecticide applications (untreated control and applications in the 'fall,’ 'spring,’ 'fall + spring,' and 'fall + spring + summer'). Flight activity of winged aphid alates was predicted by ordinal date in the fall and spring. Aphid and natural predator densities in field plots varied across foliar insecticide treatments. Cultivar selection and a high nitrogen rate increased YDV disease incidence across two field seasons. Significant yield reductions were pronounced in the second year. Seed yield and economic returns were greatest for the less susceptible cultviar when fully protected with 'fall + spring + summer' insecticide treatments. A high nitrogen rate did not increase seed yield across treatment combinations in a first-year stand, although a significant increase was observed in the second year when YDV infection averaged >50%. Selecting resistant cultivars and reducing aphid populations during the fall and spring aphid flights is critical for maximizing seed yield potential in perennial ryegrass grown for seed. Research on YDV-resistant phenotypes and resistance mechanisms in perennial grass seed crops is needed. Our findings are the first to provide an integrated pest management framework for controlling YDV disease in perennial grass crops grown for seed and will inform ongoing research on host plant resistance in this production system.