INTERACTIONS OF FUNGICIDE AND INSECTICIDE COMBINATIONS AGAINST RHIZOCTONIA DAMPING-OFF AND ROOT-ROT IN CANOLA

In growth chamber pot experiments with soilless mix infested with an i solate of Rhizoctonia solani AG2-1, two seed-dressing insecticides (cl oethocarb and gamma-HCH) and two granular insecticides (carbofuran and terbufos) were tested alone and in combination with five seed-dressin g fungicides (carboxin, cyproconazole, furmecyclox, iprodione and tolc lofos-methyl) against pre-emergence damping-off and post-emergence see dling root rot in canola cv. Westar (Brassica napus). Each fungicide p rovided almost complete control of damping-off, but, against post-emer gence root rot, furmecyclox, iprodione and tolclofos-methyl gave far b etter control than carboxin and cyproconazole. Cloethocarb and carbofu ran increased the incidence of damping-off and, when used in combinati on with fungicides, lowered the disease control against damping-off an d root rot. Gamma-HCH and terbufos decreased the incidence of pre-emer gence damping-off, and terbufos also reduced post-emergence root rot. Combined treatments with gamma-HCH and terbufos gave better control ag ainst damping-off than either gamma-HCH or terbufos alone. Disease con trol by fungicides against both damping-off and root rot was enhanced by the use of either gamma-HCH or terbufos together with fungicide tre atments. Fungicide combinations with gamma-HCH and terbufos were at be st additive in their activity for overall disease control. Maximum dis ease control with insecticide-fungicide combinations was achieved when terbufos granules were applied at the time the pots were sown with fu ngicide + gamma-HCH-treated seed. Adding terbufos granules to the trea ted seed 1-4 wk before seeding, resulted in a considerable loss of eff icacy of each of the five fungicide + gamma-HCH seed treatments.