Low effectiveness of biocontrol of Rhizoctonia solani in poinsettia

摘要

Two experimental trials to control Rhizoctonia solani on poinsettia (Euphorbia pulcherrima cv. Cortez) were carried out during August-November 2001. The following biological products were tested: Bacillus subtilis F3, Trichoderma spp., Trichoderma harzianum T39 and Trichoderma harzianum T22 [application rates not specified]. A chemical fungicide, tolclofos-methyl, was applied as a control drench (125 g/100 litres) after transplanting. In the first trial antagonists were added to the substrate before artificial inoculation with the pathogen. In the second trial, antagonists were either mixed into an infected substrate (previously inoculated with 1.0, 2.5, or 5.0 g of infected wheat kernels per kg of substrate), or used as a root dip for cuttings ofpoinsettia before they were potted into the infected substrate. The results showed high and constant effectiveness of tolclofos-methyl, while the different strains of Trichoderma harzianum and Bacillus subtilis showed very low activity against the pathogen.