Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/7/2004
Publication Date: 1/5/2005
Citation: Wilkerson, G.G., Price, A.J., Bennett, A.C., Krueger, D.W., Roberson, G.T., Robinson, B.L. 2005. Evaluating the potential for site-specific herbicide application in soybean (glycine max). Weed Technology. 18:1101-1110. Interpretive Summary: Soybean growers typically control weeds by applying a single or combination of herbicides at a single rate to an entire field. Growers could save money if herbicides were applied in a site-specific manner, varying herbicides and rates depending on the weed species present within areas of a field. An experiment was conducted to evaluate the potential for site-specific herbicide application in soybean as well as determine if limited, and thereby cheaper, weed scouting data could be used to identify fields that might benefit from site-specific weed management. Results show that site-specific weed management increased weed control and saved money. Results also show that sampling as few as 10 spots per field may provide enough information to identify fields that would benefit from site-specific herbicide application.
Technical Abstract: Field experiments were conducted on two North Carolina research stations in 1999, 2000, and 2001; on-farm in Lenoir, Wayne, and Wilson Counties, North Carolina in 2002; and on-farm in Port Royal, VA in 2000, 2001, and 2002 to evaluate possible gains from site-specific herbicide applications at these locations. Fields were scouted for weed populations using custom software on a handheld computer linked to a Global Positioning System (GPS). Scouts generated field specific sampling grids and recorded weed density information for each grid cell. The decision aid HADSSTM was used to estimate expected net return and yield loss remaining after treatment in each sample grid of every field under differing assumptions of weed size and soil moisture conditions, assuming the field was planted with either conventional or glyphosate resistant (GR) soybean. The optimal whole-field treatment (that treatment with the highest expected net return summed across all grid cells within a field) resulted in average theoretical net returns of $79 and $139/ha for conventional and GR soybean, respectively. When the most economical treatment for each grid cell was utilized in site-specific weed management, theoretical net returns by $13 (conventional) and $4.50/ha (GR) and expected yield loss after treatment was reduced by 10.5% and 4%, respectively. When the most effective treatment for each grid cell was utilized in site-specific weed management, theoretical net returns decreased by $18 (conventional) and $4/ha (GR) and expected yield loss after treatment was reduced by 27% and 19%, respectively compared to the whole-field optimal treatment. Site-specific herbicide applications could have reduced the volume of herbicides sprayed by as much as 70% in some situations, but increased herbicide amounts in others. On average, the whole-field treatment was optimal for only 35% (conventional) and 57% (GR) of the grid cells.