Abstract
Thionazin and mesulfenfos belonging to nematicides were injected into ll-year-old Japanese black pine, diseased with pine wilt disease by the inoculation of pine wood nematode 2, 5, and 6 weeks before the nematicides treatment, with the following results. In the standing trees, the following were observed : 1) Recovery of pine resin exudation and high survival rate in the thionazin- and mesulfenfos-injected trees two weeks after the nematode inoculation, 2) Recovery from the stagnation of thickening growth in the recovered trees, 3) Partial death of trees in the recovered and survived trees, and 4) Surrounding with under-bark necrosis composed of innerbark and cambium in the base of the dead branches of the partially died trees. In the cross-section, no water conducted vascular patch or brown colored stains from pith were observed. Under-bark necrosis occurred where brown colored stains were found till the annual rings made in the year when curative experiments were conducted. The results of the curative nematicides injection experiment showed that there are two disease development stages. In the first stage, recovery from the disease can be expected with the nematicides treatment because it is reversible as cambium cells remain alive despite the cessation of pine resin exudation and the stagnation of thickening growth. However, in the second stage, the possibility of recovery with nematicides treatment falls rapidly because of the development of brown colored stains which cause the death of cambium to extent from part to the whole body.
