Cabbage Refuse Piles as Sources of Inoculum for Black Rot Epidemics. C. G. Kocks, Department of Phytopathology, Wageningen Agricultural University, P.O. Box 8025, 6700 EE Wageningen, the Netherlands. J. C. Zadoks, Department of Phytopathology, Wageningen Agricultural University, P.O. Box 8025, 6700 EE Wageningen, the Netherlands. Plant Dis. 80:789-792. Accepted for publication 25 March 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0789.

During three consecutive years, the effects of cabbage refuse piles infected with the bacterium Xanthomonas campestris pv. campestris on black rot epidemics in cabbage were investigated. Field plots of cabbage were infested by placing old (4 month old) or fresh (2 week old) refuse piles in the center. Infection of the plots from seed and from unknown sources in or around the plots could be excluded by appropriate experiments, farm history analysis, and visual observation. Black rot development in the plots was far more intensive with fresh than with old refuse piles. During all 3 years, cabbage plots infested with old refuse piles had 1% diseased plants per plot and an average of 0.02 diseased leaves per plant. In contrast, fresh refuse piles resulted in 30 to 70% diseased plants and 1.0 to 3.5 diseased leaves per plant. Typical disease foci developed around the fresh refuse piles. Black rot development was positively correlated to the number of days with rainfall between 0600 and 0900 h during May and June. Refuse piles are common in Dutch growing areas and thus may be serious sources of inoculum for black rot epidemics.