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Disease Control and Pest Management

Economic Evaluation of Fungicides for Control of Alfalfa Foliar Diseases. S. C. Broscious, Former graduate research assistant, Department of Plant Pathology, University of Illinois at Urbana-Champaign, Urbana 61801; H. W. Kirby, Associate professor, Department of Plant Pathology, University of Illinois at Urbana-Champaign, Urbana 61801. Phytopathology 78:934-939. Accepted for publication 8 February 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-934.

Benomyl, copper hydroxide, or mancozeb were applied to 10 consecutive cuttings of the alfalfa cultivar Phytor from 1983 through 1985 using various schedules. Disease severity at harvest was reduced by all fungicide:schedule combinations. Disease control improved as the number of applications per cutting was increased. All treatments except mancozeb or benomyl applied 10 days before harvest and all copper hydroxide treatments had higher yields than the control. Several treatments had higher stand densities than the control at the end of the study. Zero, one, two, or three applications of mancozeb at weekly intervals beginning after 1014 days of regrowth were evaluated in 1985 on three cuttings of the alfalfa cultivars Raidor and Vernal. All fungicide treatments reduced area under disease progress curve and final disease severity. Dry matter yield of the control was lower than the fungicide treatments, which were not statistically different from each other. The most profitable treatment was a single application of mancozeb after 1014 days of regrowth with a 215% return on investment and net marginal return of $20.58/ha. Maximum yield reduction in an individual trial was 52% and mean loss to foliar pathogens over all trials was approximately 15%. In both studies, Phoma medicaginis and Stemphylium botryosum were the predominant pathogens with Colletotrichum and Leptosphaerulina spp. present at lower levels.