Effective Light-emitting Diode Ultraviolet Wavelengths and Irradiation Conditions for Strawberry Anthracnose Control

Research on plant disease control using fluorescent-type ultraviolet light (UV) lamps is well established; however, UV irradiation conditions using light-emitting diode (LED)-based lamps to control plant diseases remain poorly defined. In this study, we used LED UV lamps of different wavelengths (280, 308, and 330 nm) and investigated the UV irradiation conditions that effectively controlled strawberry anthracnose. The most effective strawberry anthracnose control was achieved with 280 nm irradiation, followed by 308 nm irradiation; 330 nm irradiation had negligible efficiency. The effectiveness of UV irradiation in controlling strawberry anthracnose varied among cultivars. In ‘Tochiotome’ and ‘Sagahonoka’, the incidence of strawberry anthracnose was significantly suppressed by UV irradiation at 280 nm. However, in ‘Benihoppe’, the disease was more severe than that in the other cultivars and did not respond to UV irradiation. Strawberry anthracnose suppression was achieved when UV irradiation was applied before pathogen inoculation, but not when administered solely after pathogen inoculation. Under the specified conditions of lamp height and irradiation duration, namely 110 cm/4.5 h, 110 cm/3 h, 90 cm/3 h, and 80 cm/1.5 h, leaf scorch was minimal, and an anthracnose control effect of more than 30% was observed. Irradiation with 280 nm UV for 2, 4, 7, 10, or 14 days before pathogen inoculation for a duration of 7–14 days was effective at controlling anthracnose. When plants were irradiated with 280 nm UV for 7 days and then infected with pathogen 0–16 days later without UV irradiation, the control effect continued for up to 12 days. This study demonstrated that 280 nm UV LED irradiation effectively controls strawberry anthracnose, affecting the aboveground parts, while also demonstrating irradiation conditions that achieve high control without inducing leaf scorch.