Persistence of Aschersonia aleyrodis, a fungal pathogen of whitefly, was studied on cucumber, gerbera and poinsettia. Germination capacity and infectivity of conidia, which stayed on the plants for up to 1 month, were assessed. Average germination of conidia on the leaves was low (< 14%), whereas most of the conidia transferred from the leaf to water agar were viable, even after having been on the leaf surface for 1 month. Germination capacity was highest on cucumber, followed by poinsettia and lowest on gerbera. On cucumber leaves, conidia stayed viable and were able to infect 90% of whitefly nymphs 31 d after spore application. On gerbera, germination capacity decreased considerably from 80% (day 0) to 40% (day 31). This was reflected in nymphal mortality, which declined from 75% to 40%. Despite the high germination capacity (60%) of conidia on poinsettia after an exposure of one month, nymphal mortality decreased from 70% at the day of spore application to 10% after 3 d at leaf surface, and remained low throughout the monitoring period. Relations between germination capacity, infectivity and the host plant environment such as phyllosphere microorganisms, secondary plant metabolites and microclimate are discussed.