VELVETLEAF (ABUTILON THEOPHRASTI) INTERFERENCE IN SOYBEANS (GLYCINE MAX) AS INFLUENCED BY ROW WIDTH, TILLAGE SYSTEM AND DISEASE (COMPETITION, WEED DENSITY, NO-TILL, VERTICILLIUM DAHLIAE)

GERALD LELAND WILEY, Purdue University

Abstract

Field trials were established in 1981, 1982, and 1983 to determine the effects of row width and tillage system on velvetleaf (Abutilon theophrasti Medic.) competition in soybeans Glycine max (L.) Merr. 'Amsoy 71' . Soybeans were grown in 25 and 76 cm row spacings under conventional and no tillage conditions. In both tillage systems, soybeans grown in narrow rows suppressed the growth of velvetleaf when compared to those grown in wide rows. Tillage system influenced the growth of soybeans and velvetleaf, but did not affect their relative competitiveness. Soybeans grown with no tillage produced significantly greater seed yield in two of the three years, as did soybeans grown in narrow rows. The results suggest that a narrow row, reduced tillage production system provides soybeans with a competitive advantage over velvetleaf. During these studies, velvetleaf was relatively non-competitive at densities ranging from 2.5 to 40 plants/m('2). Subsequently, the velvetleaf was found to be infected with Verticillium dahliae Kleb. and additional trials were established in 1983 and 1984 to determine the effects of disease, and to evaluate further and influence of row width, on velvetleaf competition in soybeans. Healthy velvetleaf, at densities of 2.5 to 40 plants/m('2), significantly reduced the dry weight of soybean leaves, stems, pod and seed, and in the leaf area index, pod number, and seed yield of soybeans grown in both row widths. Soybeans grown in narrow rows reduced the growth of velvetleaf when compared to those grown in wide rows. The magnitude of growth and yield reduction caused by velvetleaf was dependent upon weed density, but was influenced by growing season, row width, and soil type. Of the velvetleaf exhibiting disease symptoms, V. dahliae was isolated from 65 to 97% of the plants tested. Some velvetleaf plants were also found to be infected with Macrophomina phaseolina Goid. Of the velvetleaf plants exhibiting wilt symptoms, 96% were found to be infected with both pathogens concurrently. Only 4% of the soybean plants tested were infected with V. dahliae and none were infected with M. phaseolina. Diseased velvetleaf, at densities of 2.5 to 40 plants/m('2), caused 1.5 to 8.5% reduction in the seed yield of soybeans, while healthy velvetleaf reduced soybean seed yield by 18.5 to 52.5%. V. dahliae reduced the leaf area and dry weight of velvetleaf by 60%, and height by 36%, when compared to healthy plants. No definite pattern of disease incidence could be attributed to row width or tillage effects.

Degree

Ph.D.

Subject Area

Plant propagation

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