Semanotus japonicus is the most severely damaging pest of Cryptomeria japonica plantations. Larvae of S. japonicus feed on the inner bark and sapwood, causing heavy losses of wood quality and price and occasional tree mortality. Resinosis by host trees and attack by natural enemies such as parasitoid wasps dominate as larval mortality factors. Populations of S. japonicus are usually established in C. japonica plantations 5-10 years after planting, reach peak abundance when the plantations are 10-20 year-old, and subsequently decline rapidly. Plantations located at lower altitudes and with larger radial increment are more susceptible to the infestation by S. japonicus. Trees resistant against S. japonicus have been selected in an extensive breeding program and their offsprings will soon be supplied. Although several preventive and control measures are proposed, the practical effectiveness of these measures has not been confirmed. Finally, potential directions for future research are discussed.
Japanese larch trees approximately 10 years old were inoculated with Ceratocystis laricicola at the Experimental Forests in Yatsugatake, Agricultural and Forestry Research Center, University of Tsukuba, Kawakami-mura, Nagano Prefecture. After the inoculation, development of the external symptoms, size of lesions on the inner bark, staining and dried zones of sapwood, disturbance of water conduction in sapwood, development of C. laricicola in sapwood and change of the xylem pressure potential of the inoculated trees were examined every week. Ceratocystis laricicola grew in sapwood radially and longitudinally. Sizes of lesions on the inner bark and blue stained and dried sapwood increased with time. There was no water conduction in the blue stained and dried sapwood. The xylem pressure potential gradually decreased. The external symptoms appeared 14 days after inoculation and at this time some of the trees were already dead. Sapwood area in which water conduction was disturbed reached more than 85% in the transverse section near the inoculation point in the dead trees. Results of this experiment indicated that C. laricicola grew in the sapwood and stopped water flow, and consequently external symptoms of the larch trees developed.
In September 1995, diseased leaves with lesions characterized as anthracnose were found on shoe flower (Hibiscus rosa-sinensis) planted on the roadside in the city of Naha, Okinawa Prefecture, Japan. These lesions were light-brown and irregular-shaped, and black and globose acervuli were formed on their surface. The lesions enlarged fast, and consequently the leaves became yellowish and finally fell off. The conidia produced in the acervuli were falcate, and are 24.5-28 µm×2.8-4 µm in size. Their pathogenicity as anthracnose was also confirmed by the inoculation test. The pathogen of these lesions was identified as Colletotrichum capsici (Sydow) Butler & Bisby, and the shoe flower anthracnose caused by this is new to Japan.