ISHS Acta Horticulturae 470: II International Symposium on Pistachios and Almonds
DIVERSE SYMPTOMS AND TREE LOSSES CAUSED BY PHYTOPHTHORA SPP. IN CALIFORNIA ALMONDS |
| Authors: | G.T. Browne, M. Viveros |
| Keywords: | Phytophthora, P. cactorum, P. citricola, P. megasperma, crown and root rot, Prunus |
| Abstract:
The role of Phytophthora spp. in almond tree mortality was investigated in several California almond districts. In the Sacramento and upper San Joaquin Valleys, tree losses due to crown rot were prevalent during the spring and summer of 1996 and 1997. P. megasperma was commonly isolated from the dying trees, which were often of nonbearing age. In the lower San Joaquin Valley, tree losses occurred in several mature almond orchards during 1994–97 and were associated with rapidly advancing aerial cankers as well as crown rot. In one of the orchards, 9% of the trees died in 1994, another 2% died by 1996, and many remaining trees were symptomatic in 1997. In five other orchards, tree losses due to the lethal cankers ranged from less than 1% to more than 10%. Laboratory isolations and pathogenicity tests implicated P. cactorum and P. citricola as causal agents of the crown rot and cankers. Field observations provided evidence for an aerial as well as a subterranean mode of attack by P. citricola, whereas P. cactorum predominately attacked the root crown. The new finding of lethal aerial cankers in addition to crown rot suggests that multiple control strategies may be needed to protect against these Phytophthora diseases of almond. | |
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