Abstract
Occurrence of Japanese pear rust on Japanese pear trees planted in the flat and extensive rice field (about 5km×4km) was generally severe in the area within 100m away from the infected trees of Chinese juniper as rust inoculum and gradually decreased with increase of distance up to 1, 500m. Under the climatically satisfactory condition to dispersal of sporidia such as heavy rainfall and strong wind, the trees planted within 1, 000m were rather severely diseased. The following relationships were detected between the distance of sporidial dispersal (x) and the percentage of diseased leaves (Y):Y=124.297e-0.002x in 1977, and Y=54.361e-0.002x in 1979. Therefore, it is concluded that the distance of sporidial dispersal for practical control may be about 1, 500m.
