Conidial discharge by C. caryigenum from heavily diseased pecan leaf and nut shuck (involucre) tissue was studied under controlled exposure to relative humidity (RH), temperature, vegetative wetness (VW) and IR radiation. Spore release was minimal as RH decreased from near saturation to 40%, but further decrease stimulated considerable spore discharge which was enhanced by exposure to IR (> 40 .mu.E .cntdot. m-2 .cntdot. s-1). Sustained periods of constant RH < 40% also favored spore release but were less favorable than RH that fluctuated above and below 40%. Spore release was stimulated by short (.apprx. 1 min) IR exposures and brief (2-min) RH changes. Spore release was recorded only as the specimen dried off or when leaf wetness was maintained < 15%. Vibration triggered spore release at low RH, especially when specimens were exposed to IR, but vibrational effects were considerably less effective than those reported previously for other hyphomycetes.