Sewage sludge effect on management of Phytophthora nicotianae in citrus

Abstract

Greenhouse and field experiments evaluated the effect of sewage sludge incorporation to the soil against Phytophthora nicotianae in cravo lemon plants. Six sludge doses, ranging from 0 to 30% (v/v), were tested per assay on plants at different developmental stages and with different pathogen inoculum levels. The increase in sewage sludge dose resulted in pH reduction, electric conductivity and soil microbial activity increases (evaluated by FDA hydrolysis and microbial respiration), and reduction in P. nicotianae recovery, both from the soil and from the plant roots. The pathogen recovery was significant and negatively correlated with soil microbial activity and electric conductivity. Better plant development was observed with sludge incorporation up to 20%. These results indicate that the incorporation of sewage sludge can suppress P. nicotianae, by nonchemical management of the pathogen and is a potential means of disposal of this residue.