Interference Between Soybeans (Glycine max) and Common Cocklebur (Xanthium strumarium) Under Indiana Field Conditions

Abstract

The effects of interference between soybeans and common cocklebur were investigated. Common cocklebur interference reduced soybean growth at each of four sample dates during the growing season. The area of interference surrounding individual common cocklebur plants within the soybean row fluctuated over time with respect to intensity and spatial distribution. Soybean growth was significantly reduced up to 10 cm away from individual cocklebur plants at 6 weeks after planting (WAP), 30 cm at 8 WAP, 20 to 30 cm at 10 WAP, and 40 cm at 12 WAP. The maximum possible distance of cocklebur influence, determined by regression analysis, also varied during the growing season. When areas of interference from adjacent cocklebur plants overlapped, the cumulative influence was found to be additive, especially late in the growing season. Soybean interference caused a 50 to 90% reduction in the size of common cocklebur plants grown within the soybean row compared to plants grown without interference. At harvest, soybean yield was reduced up to 40 to 50 cm within the row from individual cocklebur plants. The maximum distance of interference on one side of individual cocklebur plants was 75 cm. One cocklebur plant reduced soybean yield 16.0% within 1.5 m of soybean row as the result of full-season interference. Interference of common cocklebur plants spaced 60 cm apart within the row overlapped and caused an additive reduction in soybean seed yield. Across all cocklebur treatments, there was a consistent ratio of approximately 1 kg/ha loss in soybean seed yield for each 4 kg/ha of cocklebur herbage produced.