VIEW ARTICLE

Ecology and Epidemiology

Cranberry Cottonball: Dispersal Periods of Primary and Secondary Inocula of Monilinia oxycocci, Host Susceptibility, and Disease Development. P. G. Sanderson, Department of Plant Pathology, University of Wisconsin, Madison 53706, Present address: Mid-Columbia Agricultural Research and Extension Center, Oregon State University, Hood River, OR 97031; S. N. Jeffers, Department of Plant Pathology, University of Wisconsin, Madison 53706. Phytopathology 82:384-392. Accepted for publication 21 October 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/Phyto-82-384.

In 1987–1989, airborne ascospores and conidia of Monilinia oxycocci, the causal agent of cranberry cottonball, were trapped, and selected environmental parameters were monitored in a heavily infested commercial cranberry bed. In each year, each type of spore occurred in a single dispersal period that lasted 25–35 days. Single, distinct spore showers that lasted 10–14 days occurred in each dispersal period. Ascospore dispersal periods began just before or at budbreak and continued until 0–7 days before bloom. Conidium showers began 32–33 days after initiation of ascospore showers. The presence of ascospores and conidia in the air exhibited a diurnal periodicity. Ascospores were trapped predominantly between 1000 and 2100 h, with a peak occurring between 1600 and 1800 h. Conidium concentrations peaked between 1000 and 1800 h. Temperature of the duff and upper canopy and relative humidity correlated best with the daily presence of airborne ascospores during the peak period of dispersal. These three variables and wind speed correlated best with the daily presence of airborne conidia during the peak period of dispersal. Percentage of bloom and of shoots with symptoms of primary infection were highly correlated with conidium shower intensity in both 1988 and 1989. Trap plants were placed in the field during the periods of ascospore dispersal in 1989 and 1990 and conidium dispersal in 1989. Shoots that were beginning to expand and had several nodes visible were most susceptible to infection by ascospores. Shoots inoculated with conidia did not develop tip blight symptoms. Ascospores were shown for the first time to infect flowers and cause typical cottonball fruit rot. In the field, fruit rot incidence did not change over time as berries developed, and airborne inocula were not present after bloom. This evidence supports previous observations that fruit rot results only from infection of flowers during bloom.