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Effects of Environment on Infection of Florists’ Carnation by Gibberella zeae. R. W. Stack, Department of Plant Pathology, Cornell University, Ithaca, NY 14853, Present address of senior author: Department of Plant Pathology, North Dakota State University, Fargo, ND 58102; R. K. Horst(2), P. E. Nelson(3), and R. W. Langhans(4). (2)Department of Plant Pathology, Cornell University, Ithaca, NY 14853; (3)Department of Plant Pathology, The Pennsylvania State University, University Park, PA 16802; (4)Department of Floriculture and Ornamental Horticulture, Cornell University, Ithaca, NY 14853. Phytopathology 68:423-428. Accepted for publication 14 September 1977. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-423.

Experiments were done to determine the effects of temperature, light, and humidity on infection of carnation by Gibberella zeae, causal agent of Fusarium stub dieback. The incidence of infection was the same at 13 or 18 C, but was significantly higher at 24 C. Severity of infection also was greater at 24 C than 18 C and was less at 13 C than 18 C. Incidence of infection was significantly lower at 50% relative humidity than at higher humidities. Intermittent wetting or presence of a saturated atmosphere for a short period following inoculation increased infection frequency. The combination of high temperature (24 C) and intermittent high humidity resulted in the greatest incidence and severity of infection. Growing plants at high light intensity prior to inoculation resulted in more disease than in plants grown at lower intensity. These results explain the common observation that Fusarium stem rot and stub dieback is frequently a problem in early summer in the eastern United States where conditions of temperature, humidity, and light are most favorable for infection and pathogenesis of carnation by G. zeae.