In tests of LED lights with a peak at 308 nm (UVL308) and 311 nm (UVL311) to control strawberry powdery mildew and strawberry anthracnose, in winter and fall with moderate disease incidence, the preventive value of UVL308 against powdery mildew was 91.9 and 86.9, respectively, much higher than those of UVL311 (74.8, 61.0, respectively). In contrast, in the spring, when the incidence of powdery mildew is high, the preventive value for UVL308 was 62.4 and 64.5 for UVL311, suggesting the need for additional fungicide. Analysis of these results with a generalized linear mixed model showed that the regression coefficient for UVL308 and UVL311 plots against the control plots was −1.82 and −1.55, respectively (P < 0.01). UVL308 was more effective than UVL311 in suppressing anthracnose, but its preventive value was low. Wavelengths between 290 and 310 nm accounted for 55.3% of the total irradiation for UVL308, but only 38.9% for UVL311, which may explain the difference in effectiveness between the two LED lights. Furthermore, no leaf damage was observed in any of the tests. These results indicate that UVL308 is highly effective in suppressing strawberry powdery mildew and effective in suppressing anthracnose. In the future, LED light sources need to be developed to combine the best wavelengths to control both powdery mildew and spider mites, taking advantage of the characteristics of LED light sources that can be adjusted to a narrow wavelength range.

Apple blotch (Marssonina blotch), caused by Diplocarpon coronariae, is a major disease of cultivated apples in Japan. Here we analyzed the impact of the initiation date of primary infection and disease incidence in the previous autumn (>1% of trees had blotch in late October) on the disease incidence of early epidemics (>1% of diseased trees in late August) and late epidemics (>25% of diseased trees in late September) of apple blotch in commercial orchards in three regions of Iwate Prefecture over 25 years (1998–2022). From 1998 to 2016, primary infection typically started after the petal fall stage; however, in 2017–2022, primary infection began during the bloom stage. To investigate the risk factors associated with the occurrence of apple blotch during early and late epidemics, we performed logistic regression analyses with disease incidence of early and late epidemics as response variable and the disease incidence in the previous autumn and the bloom stage infection as explanatory variables. In the orchard-level analyses of 863 orchards, the disease incidence during both early and late epidemics could be explained by a primary infection model that takes into account the presence or absence of infection at the bloom stage and disease incidence in the previous autumn as explanatory variables. Similarly, in regional-level analyses of 75 region–year cases (3 regions × 25 years), a “high” percentage of orchards with disease during late epidemics (>43.3%) could be explained by the primary infection model, with infection at the bloom stage and “high” percentage of the orchards having disease incidence in the previous autumn (>60.9%) as explanatory variables. The goodness of fit for the primary infection model and the secondary infection model at the regional level was high, with a respective accuracy rate of 87% and 88%. These results indicate a strong association of disease incidence during late epidemics with the timing of primary infection in the current year. In particular, infection during the bloom stage infection was identified as a significant risk factor contributing to widespread occurrence of the disease.