Controlling Rhizoctonia solani in Cucumber Using Compost of Agro-Industrial Residues

This work evaluates the suppressivity of two composts from agro-industrial residues, towards Rhizoctonia solani in cucumber. Composts were prepared with orange wastes, olive marc, and grass clippings (2: 1: 1, v/v), following two composting methods: static pile with forced ventilation and mechanically turned pile (naturally ventilated). The composts were tested for suppressivity after 151, 375 and 700 days of composting. A commercial peat based substrate was used as control substrate (high moor peat, Klasmann Deilmann, Germany), previously incubated at 25 degrees C and 60 degrees C. Cucumber (Cucumis sativus L. 'Negrito') was used as test plant, sown with and without inoculation of Rhizoctonia solani. Germination percentage, disease severity and disease incidence were determined for each substrate. Disease severity and disease incidence of Rhizoctonia solani in the composts were lower than in peat. Composts showed suppressivity against Rhizoctonia solani in cucumber, from 5 months to 2 years old, with a somewhat lower suppressivity on 375 days old compost. The composting method produced no significant differences regarding disease expression. The studied composts remained suppressive for almost 2 years, and can be used to biologically reduce the effects of Rhizoctonia solani, thus contributing to a more sustainable agriculture. Results suggest that the variations observed in biological control capacity were more influenced by pH and EC of the composts, than by other factors (fiber content or microbial populations).