By Stevan Knezevic, Extension Weeds Specialist
University of Nebraska



Velvetleaf, also know as a 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, water, and nutrients. Velvetleaf competitiveness can be reduced by modifying cultural practices such as row spacing.



Narrowing row spacing allows canopy to close earlier than it would in wide rows, resulting in a higher shading effect on the weeds. Other factors, such as the timing of velvetleaf emergence relative to crop emergence, also can influence the outcome of crop and weed competition.



Generally, weeds emerging with the crop will compete more with the crop than weeds emerging later. This knowledge of weed relative emergence can be used when making management decisions.



Velvetleaf field trials



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 was 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 showed that velvetleaf produced much less dry matter and had about 60-percent-less leaf area in narrow rows than in wide rows. By producing less dry matter and leaf area, the weed uses fewer resources. Velvetleaf emerging at the cotyledon stage (VC) of soybean produced 65-percent more dry matter than the velvetleaf that emerged at the V1 (1st trifoliate) stage.



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 reduced by 47 percent, 38 percent, and 15 percent when grown with velvetleaf emerging at the VC, V1, and V3 soybean stages, respectively.



Applying the research on-farm



The practical implication of this study is that planting narrow row soybeans will increase the crop's 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 a North Central Regional Weed Science grant.



SOURCE: University of Nebraska.