Relationship of Soil Temperature and Moisture to Development of Phytophthora Root Rot of Azalea

Temperature and moisture effects on development of Phytophthora root rot of azalea caused by Phytophthora cinnamomi was compared for plants growing in containers and a landscape bed in both sun and shade environment. Symptoms of Phytophthora root rot developed earlier and disease severity was greater on plants grown in the landscape bed where soil temperature and moisture in the root zone of infected plants favored disease development. Disease severity was similar for plants in the bed regardless of exposure to the sun or shade. In container culture, disease severity was greater on plants in the shade where medium temperature was lower and moisture was greater, than on similar plants exposed to the sun.