Epidemiology and Economic Impact of Impatiens Necrotic Spot Virus: A Resurging Pathogen Affecting Lettuce in the Salinas Valley of California

Abstract

The Orthotospovirus impatiens necrotic spot virus (INSV) is a thrips-transmitted pathogen of lettuce that has rapidly emerged as a serious threat to production in the Salinas Valley of Monterey County, California. As a first step toward understanding the severity of the virus, we utilized Spatial Analysis by Distance IndicEs (SADIE) to characterize the distribution and progression of INSV outbreaks and thrips infestations in two commercial lettuce fields. In both fields, INSV incidence rapidly increased from 15.86% ± 1.77 to 80.24% ± 2.60 over the course of 7 weeks and aggregated at specific edges in both fields as early as 3 weeks after planting (Ia = 1.63, Pa = 0.0100, and Ia = 1.53, Pa = 0.0300). In one of the fields, thrips populations aggregated in areas that also experienced the most INSV (Ia = 1.2435, Pa = 0.0400, week 3; Ia = 1.4815, Pa < 0.0001, week 6; Ia = 1.5608, Pa < 0.0001, week 9), while in the second field, thrips were distributed randomly despite the aggregated effects that were observed for INSV incidence. Economic analysis estimated that the virus accounted for over $475,000 in losses for the two fields, while stakeholder surveys documented over 750 fields that experienced INSV infection during the 2021 season in Monterey County alone. These studies enhance our knowledge on the epidemiology of thrips and INSV under current lettuce production practices in the Salinas Valley, while elucidating the economic consequences and broader challenges that are associated with managing thrips-transmitted viruses.