Crop Protection 22 (2003) 1093–1097 Effect of sewage sludge on the rot and seedling damping-off of bean plants caused by Sclerotium rolfsii I. dos Santos a , W. Bettiol b, * a Centro Federal de Educa@ * ao Tecnol ! ogica do Paran ! a, CP 571, Pato Branco PR 85503-390, Brazil b Embrapa Meio Ambiente, CP 69, Jaguari ! una SP 13.820-000, Brazil Received 23 April 2002; received in revised form 1 May 2003; accepted 27 May 2003 Abstract The effect of sewage sludge at concentrations of 12.4, 24.8, 37.2, and 49.6t/ha on the severity of diseases caused by Sclerotium rolfsii upon the emergence, final stand and plant dry matter weight, the soil’s electric conductivity and microbial activity was studied in beans grown under field conditions on a dystrophic Red Yellow Ultisol. Soil was infested with 100 g/m 2 of unhulled rice containing the pathogen. Sewage sludge reduced the incidence and the severity of the diseases caused by S. rolfsii and increased emergence and the final stand of the bean plants in three bean cropping seasons. Microbial activity, measured through the hydrolysis of fluorescein diacetate and the release of CO 2 , and the electric conductivity were directly proportional to the concentration of sewage sludge. For all cropping seasons, emergence and final stand of plants were positively correlated with the microbial activity in the soil and with the soil’s electric conductivity. Sludge concentrations did not influence survival of the sclerotia for a 120-day period. No problem was detected with regard to plant development. r 2003 Elsevier Ltd. All rights reserved. Keywords: Phaseolus vulgaris; Biosolids; Organic matter; Microbial activity; Suppressive soil 1. Introduction Application of sewage sludge interferes with the soil’s physical, chemical and biological properties, and among the latter are those related to plant diseases. In this regard, incorporation of sewage sludge into the soils reduced the incidence or the severity of Sclerotinia drop on lettuce, caused by Sclerotinia minor (Lib.) de Bary (Millner et al., 1982; Lumsden et al., 1986); root rot on sorghum and sugarcane, caused by Pythium arrheno- manes Drechsler (Bettiol and Kr . ugner, 1984; Dissa- nayake and Hoy, 1999); root rot on peppers, caused by Phytophthora capsici Leonian (Lumsden et al., 1983); Fusarium wilt on cucumber and basil, caused by Fusarium oxysporum Schlecht (Lumsden et al., 1983; Ferrara et al., 1996); damping-off caused by Rhizoctonia solani K . uhn and Pythium ultimum Trow on peas and cotton (Lewis et al., 1992); dollar spot on creeping bentgrass and annual bluegrass turf, caused by Sclero- tinia homoeocarpa F.T. Bennett (Nelson and Craft, 1992); root rot caused by Pythium graminicola Subram on creeping bentgrass (Craft and Nelson, 1996); root rot of beans, cotton and radish, caused by R. solani (Lumsden et al., 1983); damping-off in cucumber seedlings, caused by Pythium aphanidermatum (Edson) Fitzp. (Santos et al., 2000); and damping-off and rot in the collar of bean plants, caused by Sclerotium rolfsii Sacc. (Santos and Bettiol, 2001). On the other hand, Kim et al. (1997) reported that sewage sludge did not interfere with the incidence of root and crown rot, caused by P. capsici on bell pepper, nor did it reduce the pathogen population in the soil. However, there are reports also of increased diseases as a consequence of sewage sludge incorporation, for example the corn stalk rot caused by Fusarium (Bettiol, 2000), and root rots caused by P. ultimum and Thielaviopsis basicola (Berk & Broome) Ferraris in beans, peas, and cotton (Millner et al., 1982). The way by which sewage sludge reduces the severity of diseases, according to reports found in most papers, seems to be related to an increase in microbial activity in the soil and to the microbiota itself comprised in the ARTICLE IN PRESS *Corresponding author. Tel.: +55-019-867-8700, fax: +55-019-867- 8740. E-mail address: bettiol@cnpma.embrapa.br (W. Bettiol). 0261-2194/03/$-see front matter r 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0261-2194(03)00140-6