Crop/weed outcomes from site-specific and uniform soil-applied herbicide applications

While uniform broadcast application (BC) of soil-applied herbicides is the norm, advances in geospatial technologies have enabled the deployment of site-specific herbicide application (SS). Since there are several, largely-untested decision rules for SS herbicide use, the objective of this work was to evaluate crop/weed outcomes and isoxaflutole use for a number of BC and SS strategies. Field experiments were established where isoxaflutole dose response functions were quantified from early-season Zea mays (L.), Sorghum bicolor (L.) Moench., and Abutilon theophrasti Medic. response data at multiple plots (64 in 1999; 62 in 2000) throughout a variable field. These data were then used to infer crop and weed outcomes from simulated application strategies, While BC and SS strategies that relied on the product label were similar in terms of total herbicide use, extent of crop tolerance, and A. theophrasti efficacy, the SS strategy resulted in a significant redistribution of herbicide. Using biologically effective doses (ED) resulted in the highest efficacy and herbicide use was highly species-dependent. By using a historical weed map of the field to guide herbicide application, herbicide use could be reduced some 20-48% when following the product label where seedlings were present, or >90% when using the ED for A. theophrasti. In order to maximize the potential agronomic benefits of SS, biological and spatial information of both the weed and soil should be taken into account.