Detection frequency of Phytophthora citricola and P. cactorum from European beech trees in New York

Phytophthora canker, caused by Phytophthora citricola and P. cactorum, is a serious disease of mature European beech in the northeastern United States. Detection of the pathogen via isolation has often proven difficult, and low isolation frequencies have further hindered understanding of the disease. The objectives of this study were to determine whether frequency of pathogen detection was independent of method (isolation on selective medium and ELISA), season (spring, summer, fall, winter), or location (4 sites in NY) and to further characterize factors (such as host cultivar and canker aspect on tree) which may affect disease development. Two hundred eleven mature trees were examined, 86 (41%) of which were cankered. Of the 86 cankered trees sampled from the summer, fall, and winter sampling dates, Phytophthora was more frequently detected by ELISA (74%) than by isolation (35%). Isolation frequency was not independent of season. Phytophthora was most easily isolated in the fall, when 27 (37%) of 73 tested trees yielded cultures. Conversely, detection frequency by ELISA was independent of season, with 71-82% of the cankered trees testing positive at each sampling period. Frequency of detection was independent of location, regardless of the method used. No effects of host cultivar or trunk canker aspect on canker frequency were detected.