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Soybean response to weed interference and defoliation

Published online by Cambridge University Press:  12 June 2017

Charles F. Grymes
Affiliation:
Department of Plant Pathology and Crop Physiology, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge, LA 70803
David J. Boethel
Affiliation:
Department of Entomology, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge, LA 70803
B. Rogers Leonard
Affiliation:
Macon Ridge Research Station, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Winnshoro, IA 71295–5719
David L. Jordan
Affiliation:
Crop Science Department, North Carolina State University, Raleigh, NC 27695–7620
John S. Russin
Affiliation:
Department of Plant Pathology and Crop Physiology, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge, LA 70803

Abstract

Field experiments were conducted in Louisiana over 2 yr to evaluate the influence of full-season interference from johnsongrass, common cocklebur, or hemp sesbania at densities of 2.5, 0.5, and 2.0 plants m–1 of row, respectively, and simulated insect defoliation of soybean on weed and soybean growth. Defoliation at R2 (full bloom) and R5 (beginning seed development) soybean growth stages was accomplished by removal of zero, one, or two leaflets per soybean trifoliate, which approximated 0, 33, and 66% defoliation, respectively. Height and dry weight of all weeds were not affected by soybean defoliation level or defoliation stage. Soybean height 3 wk after defoliation at R5 was not influenced by weed interference, soybean defoliation level, or defoliation stage in either year. Averaged across soybean defoliation levels and stages in 1994, johnsongrass, common cocklebur, and hemp sesbania reduced soybean yields 30, 15, and 14%, respectively. In 1995, johnsongrass reduced soybean yield 35%. As soybean defoliation level increased, a linear decrease in soybean yield was observed. Averaged across weeds and soybean defoliation stages, 33 and 66% defoliation reduced soybean yield 6 and 20% in 1994 and 12 and 33% in 1995, respectively. Defoliation at R5 resulted in 10% lower yield than defoliation at R2 in one of two years. Yield reduction due to combinations of weeds and soybean defoliation was additive.

Information

Type
Weed Biology and Ecology
Copyright
Copyright © 1999 by the Weed Science Society of America 

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