Effect of metalaxyl on the control of Phytophthora crown rot of almonds

The fungicide Ridomil (5% a.i. metalaxyl), applied at 100 g per tree in spring, winter and autumn in a shallow circular trench around and close to the trunk, prevented the development of trunk cankers and reduced the incidence of dead almond trees caused by Phytophthora cambivora. Metalaxyl prevented infection of healthy trees but did not rejuvenate trees that were declining at the time of application. Bioassays and chemical analysis of soil showed that most of the metalaxyl was concentrated in the top 10 cm of soil. In some soils, 20 mg metalaxyl/kg soil was detected 46 weeks after application.