Abstract

Selected Trichoderma and Bacillus isolates were tested as seed treatments with reduced concentrations of tolclofos-methyl against Rhizoctonia solani damping-off using cucumber as test plants. In vitro bioassays using filter paper disc infused with six concentrations [active ingredient (ai)] of tolclofos-methyl (0.005, 0.05, 0.125, 0.25, 0.5 and 1.5 g ai/l) showed that growth of Trichoderma isolates on agar plates were less inhibited at 0.005 and 0.05 g ai/l than 0.125 – 1.5 g ai/l tolclofos-methyl concentrations while Bacillus isolates were not affected by any of the six concentrations. In a greenhouse study with a 0.05 g ai/l tolclofos-methyl concentration, Trichoderma and Bacillus isolates applied alone or in combination to cucumber seeds resulted in a better disease control than the Trichoderma andBacillus treatments used alone. As high as 86% disease control was achieved by combining 0.05 g ai/l tolclofos-methyl with T. harzianum Isolate SYN which was significantly better (P = 0.001) than the 0.05 g ai/l tolclofos-methyl control. In all cases, additive effects of combining 0.05 g ai/l tolclofos-methyl with Trichodermaand Bacillus treatments were observed.

Key words: Active ingredient (ai), bacillus, damping-off, tolclofos-methyl,Trichoderma.