Optimization of timing and frequency of application of the antagonist Ulocladium atrum for management of gray mold in potted rose under high disease pressure

One to four applications of the antagonist Ulocladium atrum 302 were made to determine the effective timing and frequencies of applications needed to reduce the sporulation of Botrytis cinerea on potted roses under conditions conducive to development of gray mold. Potted rose foliage is maximally susceptible to B. cinerea infection when cuttings are rooted, just after rooting when vapor pressure deficits are changing and during and just after trimming of vegetative growth. Three independent trials were performed, with eight blocks each, and efficacy of treatments was assessed 2 weeks after the final application. A single application of U. atrum significantly reduced disease incidence and sporulation, but increasing numbers of applications increased effectiveness. No effect was observed on pathogen’s sporulation until the third application date, subsequent to wounding and the incomplete removal of senescent tissues. Hence, under conditions of high disease pressure, application of U. atrum can be delayed until cuttings are well established and fresh infection courts become available due to horticultural practices.