Japanese oak wilt disease carried by Platypus quercivorus has been growing since the 1980s. Although climate conditions are sometimes mentioned as an explaining this expansion, there is no statistical analysis to support this notion. Given this, we examined the relationship between the annual number of killed oak trees and climate conditions with a single regression analysis that was based on the results of damage surveys conducted in Kyoto City and Maizuru City, Kyoto Prefecture. As a result, we found that, in both areas, there is a tendency for the number of killed oak trees to increase in line with increases in the maximum temperature during the coldest period (i.e., from January to February). Additionally, in Kyoto City, there is a tendency for damage to increase correspondingly with higher amounts of spring precipitation. Moreover, in Maizuru City, there is a tendency for the number of killed oak trees to increase correspondingly with increases in the number of days that have a low temperature of at least 20°C between June to July. However, results supporting the common opinion that high temperature and light rain in summer promote Japanese oak wilt disease were not obtained.

The pathogenicity and infection route of a frosty mildew fungus Redheadia quercus in leaves of 10 fagaceous tree species were investigated by inoculating onto the detached leaves. The fungus developed discolored areas in the leaves of deciduous Quercus, Castanea and Fagus and evergreen Quercus, Castanopsis and Lithocarpus species, and was reisolated from the areas except Q. dentata. The result showed that the fungus may have pathogenicity to a wide range of both deciduous and evergreen fagaceous tree species. Microscopic observations revealed that the fungus invades the host leaves through stomata.

To evaluate the effectiveness of trunk injection of nematocide to the endangered pine species, Pinus armandii var. amamiana, we injected a liquid formulation of morantel tartrate into 44 living trees and monitored their survival and health for 7 years. While several untreated P. armandii var. amamiana and P. thunbergii trees died due to pine wilt disease at the three study sites in Tanega-shima, all but one of the treated trees survived and the pinewood nematode was not detected in the dead tree. None of the treated and untreated trees at the two study sites in Yaku-shima died due to pine wilt disease. The concentration of nematocide in the treated trees at 1 to 3 years after initial administration ranged from 4.0 to 210.4ppm, which is sufficient for preventing pinewood nematode multiplication. No symptom of injury caused by the administrated nematocide was observed. The results showed that the trunk injection of nematocide was effective for preventing pine wilt disease of P. armandii var. amamiana, and was thus useful for in situ conservation of this endangered tree species.