All stems of geranium (Pelargonium X hortorum) stock plants inoculated with Botrytis cinerea and incubated in a dew chamber under conditions conducive for disease development within 12 hr of excising cuttings (stem wounding) became blighted. Disease incidence maxima were 38 and 29% when plants were inoculated 1 and 3 days, respectively, after stem wounding and placed in an environment of low relative humidity (RH < 60%) before incubation in a dew chamber. The area under the incidence of stem blight disease progress curve (AUDPC) revealed a minimum of 1 day in an environment of low RH between stem wounding and subsequent inoculation and incubation in a dew chamber was necessary to significantly limit stem blight incidence. When averaged, at least 94% of the stems became blighted when plants were exposed to an environment of low RH for 1 day after inoculation, before incubation in a dew chamber. When plants were inoculated and subjected to an environment of low RH for 3, 5, and 7 days before incubation in a dew chamber, an average of 69, 85, and 50% of the stems, respectively, became blighted. According to the AUDPC data, when inoculated plants were placed in an environment of low RH for a minimum of 1 day before incubation in a dew chamber, stem blight incidence was significantly limited. The AUDPC data indicated that the longer inoculated plants were maintained in an environment of low RH before incubation in a dew chamber, the lower the stem blight incidence.
