Site-Specific Weed Management in Corn (Zea mays)1

Site-specific weed management can increase crop production efficiency by minimizing herbicide input costs without compromising crop yields. A reduction in herbicide inputs resulting from site-specific weed management may also decrease the probability level of nonpoint pollution compared with conventional herbicide applications. A 4.5-ha field was selected to compare site-specific and conventional weed management techniques in 1997 and 1998 at Knoxville, TN. Variable rate applications (VRAs) of atrazine preemergence (PRE) followed by dicamba postemergence (POST) were investigated for the reduction of herbicide inputs and their resulting impact on weed control and corn yield. VRAs of atrazine were on the basis of weed density data collected in 1996. VRAs of dicamba were according to common cocklebur density evaluations within the field. Compared with conventional applications, atrazine usage was decreased by 43 and 32%% in the site-specific application treatments in 1997 and 1998, respectively. VRAs of dicamba reduced herbicide inputs by greater than 45%% for 1997 and 1998. Corn yields were similar for the conventional and site-specific treatments in both years. On the basis of these data, site-specific herbicide applications have the greatest potential and least risk for managing weeds when POST or PRE ++ POST variable rate herbicide applications are used.Nomenclature: Atrazine; dicamba; common cocklebur, Xanthium strumarium L. ##³ XANST; corn, Zea mays L. ‘‘Dekalb 689’’.Additional index words: Brachiaria platyphylla (Griseb.) Nash, broadleaf signalgrass, geographical information systems, global positioning systems, variable rate application.Abbreviations: DGPS, differential global positioning system; GIS, geographic information system; OM, organic matter; POST, postemergence; PRE, preemergence; VRA, variable rate application.