Emergence and Yield of Fungicide‐Treated Soybean Seed Differing in Quality1

Abstract

AbstractCurrent recommendations that soybean (Glycine max L. Merr.) seeds be treated with fungicides if they are of poor quality or to be planted in cool, wet soils, are too vague for the grower to be sure when treatment is warranted in the upper Midwest. This paper evaluates the effects of fungicide treatments on seeds with different quality characteristics under more precisely‐defined soil conditions than in previously reported studies. Seedlots of ‘Cumberland’, ‘Wells’, and ‘Williams’ with inferior quality due to age, damage, small size, or infection by Phomopsis spp. were treated with captan {N(trichloromethyl)‐thio]‐4 cyclohexene‐1,2‐dicarboximide}, carboxin‐thiram (5,6‐dihydro‐2‐methyl‐1, 4 oxathiin‐3‐carboxanilide, 17%; tetramethylthiuram disulfide, 17%), metalaxylN‐(2,6‐dimethylphenyl)‐N‐(methoxyacetyl) alanine methyl ester) or untreated. These were tested for emergence and yield in the field on two soil types [a poorly drained Webster silty clay loam (fine‐loamy, mixed, mesic, Typic Haplaquolls), and a well drained Clarion loam (fine‐loamy, mixed, mesic, Typic Hapludolls)] at three different planting times in both 1980 and 1981. Captan and carboxin‐thiram seed treatments were equally effective in increasing emergence in the laboratory and field of soybean seedlots with more than 15% Phomopsis spp. infection, but metalaxyl did not. No seed treatment consistently improved field emergence of seeds with reduced quality because of mechanical damage, age, or size. There were no obvious differences in fungicide performance in relation to planting dates or soil types. Increased yield in response to fungicide seed treatment was detected only in the 50% Phomopsis‐infected seedlot. We conclude that fungicide seed treatment cannot be justified on seeds of low quality for reasons other than disease under most of the soil conditions likely to occur in the upper Midwest. These results suggest that performance of seedlots with Phomopsis spp. infection exceeding 15% will be improved by fungicide seed treatment.