A Precision Weed Management Approach to Minimize Impacts.

By bringing together information about weed spatial distribution and competitiveness, sprayer application technologies, and economics, we can begin to develop a precision weed management approach that minimizes our agricultural footprint. A number of challenges arise; one, get good information about the spatial distribution of weed populations and two, ensure that adequate weed control is obtained. We have proposed a two-pass system: variable or low rate soil-applied herbicide, followed by a map-based, foliar-applied herbicide. Soil texture, organic matter, and pH can interact with soil-applied herbicides and determine the amount of chemical available for plant uptake compared to that bound to soil particles. This would still require application across the entire field. The next level of sophistication would be to tie in occurrence of weed seed bank populations. Precision application of postemergence herbicides is possible with a map of weed populations across the field. The challenge is to obtain an accurate map (weed species and density) at an appropriate resolution (grid cell = boom section or individual nozzles). Once we have an accurate weed species and density map, the “economically optimal rate” to apply in each grid cell was determined using algorithms programmed into a spreadsheet. The economically optimal rate may be below-label, however research has determined that below-label rates are effective as part of an IWM plan including timeliness of application, match rate to weed species and density, and establishing competitive crops. Other researchers have suggested using remote or on-the-go-sensing as information sources for making weed maps. Obtaining an accurate weed species and density map is a critical limiting component of implementing precision weed management; however it is clearly an approach that focuses our efforts on where the weeds occur and protects the areas where weeds do not occur.