Numbers of airborneMonilinia laxaconidia were related to the maturity of the sporodochia, the nature of the host structure bearing them, and the presence or absence of rain or fog. Hirst spore traps collected more airborne conidia during rains and on rainy days than on dry days among prunaceous hosts during the spring of 1966 and 1967. Numbers of conidia were greatest (6440ensp;mminus;3ensp;hminus;1) in the first 3ndash;4ensp;h of rain, while in dry periods, numbers were greatest (1200ensp;mminus;3ensp;hminus;1) when ambient humidity was lowest and temperature and wind speeds were highest. Fruit mummies, twig cankers, limb cankers, pedicels, and peduncles all bore sporodochia. Rains washed off successive crops of conidia, and with 52ensp;800 conidia cmminus;2were collected directly below a sporulating peach fruit mummy. The significance of these dispersal periods in disease development and control is discussed.
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