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Significance of Thinned Fruit as a Source of the Secondary Inoculum of Monilinia fructicola in California Nectarine Orchards

May 1997 , Volume 81 , Number  5
Pages  519 - 524

Chuanxue Hong , Department of Plant Pathology, University of California Davis, Kearney Agricultural Center, Parlier, 93648 ; Brent A. Holtz , University of California Cooperative Extension, Madera, 93637 ; and David P. Morgan and Themis J. Michailides , Department of Plant Pathology, University of California Davis, Kearney Agricultural Center, Parlier, 93648



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Accepted for publication 10 February 1997.
ABSTRACT

The significance of thinned fruit as a source of secondary inoculum in the spread of brown rot, caused by Monilinia fructicola, under semi-arid weather conditions of the San Joaquin Valley in California, was investigated in seven nectarine orchards in 1995 and 1996. Between 6 and 60% (depending on the orchard) of thinned fruit showed sporulation by M. fructicola. Brown rot was significantly less severe at preharvest (five orchards) and postharvest (one orchard) on fruit harvested from trees in plots from which thinned fruit were completely removed than on those in plots from which thinned fruit were not removed. M. fructicola sporulated more frequently on thinned fruit placed into irrigation trenches than on those left on the dry berms in tree rows. The incidence of preharvest fruit brown rot increased exponentially as the density of thinned fruit increased on the orchard floor. These results suggest that thinned fruit left on the floor of nectarine orchards can be a significant inoculum source of secondary infections. Removal or destruction of thinned fruit should reduce brown rot in nectarine and possibly other stone fruit orchards under semi-arid California conditions.


Additional keywords: disease control, epidemiology, Prunus, stone fruits

© 1997 The American Phytopathological Society