Use of Prochloraz and Benomyl Drenches to Assess the Effects of Fungal Root Pathogens on Growth of Red Clover Under Field Conditions.

Abstract

Prochloraz (1.15 or 3.46 g/m2) or benomyl (3.46 g/m2) were applied as drenches in water to newly sown field plots of red clover (Trifolium pretense) in an experimental block known to contain several soilbome pathogenic fungi. Plants were sampled 6, 12, 18, and 45 weeks after sowing for growth measurements, and fungal populations in roots were determined using a maceration/plating technique. Compared with plants from plots receiving only water, those from fungicide-treated plots had greater shoot weights (from 6 weeks) and root weights (from 18 weeks). The greatest shoot and root weights recorded throughout the experiment were from plots treated with the higher rate of prochloraz. Total numbers of fungal colonies per gram of root were lower in plants from fungicide-treated plots than from untreated plots at all harvests. Of the fungi known to be pathogenic to red clover roots, the numbers of colonies per gram of roots of Cylindrocladium scoparium, Fusarium oxysporum, F. solani, and Trichocladium basicola, but not Verticillium dahliae, were lower in plants from fungicide-treated plots than from untreated plots at one or more harvests.