Abstract
The preventive effect of benomyl on oak wilt disease was evaluated in Yamagata, Nagano and Niigata prefectures in Japan from 2004 to 2008. In Yamagata, a dilution of benomyl wettable powder in water (a.i benomyl 2 µg/mL) was directly injected into the trunks of non-damaged healthy Japanese oak trees in June. A month later, Japanese oak wilt fungus Raffaelea quercivora was inplanted into the trunks. Twelve weeks later, all of the benomyl-inoculated trees remained alive, and the fungus was recovered from a few of them. Most of the non-injected trees died, and the fungus was reisolated with very high frequency. Benomyl wettable powder diluted with water by five hundred numbers was injected into living trees during a total of fourteen tests on eight fields in three prefectures. As for mortality rate, a clear and significant difference between the examination section using benomyl and the control was not found on Fisher's Exacts test. However, the mortality rates of all the examination districts where benomyl was used were lower than the control areas up to three years after the injections. Therefore, trunk injections of benomyl suggested a higher preventive effect against Raffaelea quercivora.
