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Ecology and Epidemiology

Ecology and Epidemiology of Pecan Downy Spot. W. D. Goff, Former graduate research assistant, Department of Plant Pathology and Physiology, Clemson University, Clemson, SC 29634-0377; C. E. Drye, and R. W. Miller. Associate professor and professor, Department of Plant Pathology and Physiology, Clemson University, Clemson, SC 29634-0377. Phytopathology 77:491-496. Accepted for publication 12 September 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-491.

Conidia and ascospores of Mycosphaerella caryigena were trapped in a Stuart pecan orchard throughout the season. Ascospores were present before bud break in the spring. Maximum release occurred in late April, after which numbers dropped until few were trapped after mid-June. Conidia were present in low numbers in the spring and early summer. Maximum numbers of conidia were trapped in late June and early July with smaller numbers released the remainder of the season. Maximum conidial production on diseased leaves occurred at 18–25 C and at a relative humidity of 90–98%. Some conidia were produced throughout the range of the test, from 70 to 100% and from 11 to 32 C. Conidial germination and leaf penetration occurred at temperatures of 20, 26, and 31 C and with maximum germination and penetration at a relative humidity of 99–100%. Light was not essential for either conidial production or germination. Disease incidence was highest in the lowest parts of the tree. This difference was most distinct in early season and became less as the season progressed.