Evaluation of Phenamacril and Ipconazole for Control of Rice Bakanae Disease Caused by Fusarium fujikuroi

This study evaluated the use of phenamacril and ipconazole, alone and in mixtures, for the control of rice bakanae disease caused by Fusarium fujikuroi. Mixtures were studied with the goal of reducing the selection of fungicide-resistant field isolates of the fungus. When tested alone, both phenamacril and ipconazole exhibited high antifungal activity against F. fujikuroi mycelial growth; the average EC 50 value for 19 field isolates was 0.1544 μg/ml for phenamacril and 0.0472 μg/ml for ipconazole. A 2:1 mixture of phenamacril and ipconazole caused a slightly synergistic (greater than additive) inhibition of mycelial growth. Inhibition of F. fujikuroi sporulation was highest for ipconazole alone, intermediate with the 2:1 mixture, and lowest for phenamacril alone. Inhibition by phenamacril and ipconazole alone or by the 2:1 mixture was substantially lower for spore germination than for mycelial growth or sporulation. When the total fungicide concentration was <24 g of a.i./100 kg of treated rice seeds, the fungicides, whether alone or in the 2:1 mixture, were not phytotoxic to seeds or seedlings of two rice cultivars. In a greenhouse experiment, the 2:1 mixture of phenamacril and ipconazole at 6 g of a.i./100 kg of treated seeds provided 100% control of rice bakanae disease on two cultivars. Overall, the results indicate that the use of a 2:1 mixture of phenamacril and ipconazole should control rice bakanae disease while reducing the occurrence of fungicide resistance in F. fujikuroi.