University of Nebraska-Lincoln Extension, Institute of Agriculture and Natural Resources

July 7, 2006

Research update: How soybean row spacing affects velvetleaf competitiveness

Velvetleaf, also know as button-weed, is an important annual weed in row crops throughout the Midwest. Its fast growth rate allows it to compete with crops for growth limiting resources such as light, nutrients and water. Velvetleaf competitiveness, however, can be reduced by modifying cultural practices, including narrow row planting. Narrowing the row spacing allows the canopy to close earlier than with wide rows, resulting in higher shading effects on the weeds. Other factors, such as the time of velvetleaf emergence relative to the crop emergence, also can influence the outcome of crop and weed competition. It is logical to expect that the later emerging weeds will be less competitive than weeds emerging with the crop. This knowledge of weed relative emergence can be used when making management decisions.

We conducted field studies in eastern Nebraska at two locations in 2002 and 2003 to determine the influence of soybean row spacing and relative time of weed emergence on velvetleaf and soybean growth and competition. This study is also a Master's thesis project for Shawn Hock. Soybean was planted in 7.5- and 30-inch rows. Velvetleaf was hand planted at soybean planting (VP), emergence (VE), and 1st trifoliate (V1) stage. Observations were made throughout the growing season to determine the effects of row spacing and relative emergence on growth and development of both the crop and the weed.

The results from this study showed that velvetleaf produced much less dry matter and had about 60% less leaf area in narrow rows than in wide rows. By producing less dry matter and leaf area the weed takes fewer resources from the crop. Velvetleaf emerging at the cotyledon stage (VC) of soybean produced 65% more dry matter than the velvetleaf that emerged at the V1 (1st trifoliate) stage of crop.

Soybean yields were higher in the narrow rows, and when velvetleaf emerged later in the season. Soybean grown in 7.5-inch rows yielded 4 bushels more than soybeans in 30-inch rows. Soybean yields were also reduced by 47%, 38%, and 15% when grown with velvetleaf emerging at the VC, V1, and V3 soybean stages, respectively.

Practical implication of this study is that planting narrow row soybeans will increase the crop competitiveness against weeds, including velvetleaf. Also, an early season field scouting of weed emergence patterns relative to the crop growth stage can help determine management strategies. For example, earlier emerging weeds will require earlier weed removal.

This study was partially funded by the North Central Regional Weed Science grant.

Stevan Knezevic
Extension Weeds Specialist

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Published by University of Nebraska-Lincoln Extension in the Institute of Agriculture and Natural Resources Cooperating with the counties and the U.S. Department of Agriculture.
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