Controlling weeds in cropland fields is typically a costly and time-consuming task, but researchers at Kansas State University are working to help producers reduce those costs and curb the impact of weed control measures on the environment.
The research involves a new concept called "site-specific weed management." The idea is to match control measures to the normal patterns of weed growth, said Anita Dille, K-State Research and Extension weed ecologist.
"Weeds are almost never distributed evenly in fields – they grow better in certain areas," Dille said. "Our goal is to target postemergence herbicide applications to those areas where weeds are present, instead of the entire field."
In 2003, Dille and her team started researching variable rate spraying across fields.
"Many times, spraying the full rate of herbicide in high-density weed areas and spraying a lower rate in less-dense areas was sufficient to maintain crop yields," she said.
In some cases, spraying was not needed in sections of fields where weeds were absent.
Currently, Dille and other researchers are expanding on the research to include more weed species and a larger variety of herbicides. By determining the number of weeds and the variety of weed species in a field, Dille said they can predict yield loss and evaluate the cost-effectiveness of implementing variable rate spraying.
Making a map of where the weeds grow is one of the biggest challenges in site-specific weed management, the agronomist said. Global positioning systems (GPS) and scouting software can be particularly useful when scouting a field, because time and money isn't wasted converting hand-drawn maps to a computer.
Other site-specific weed management practices are also being examined, such as variable-rate preemergence herbicide applications, Dille said.
"Different soil types support different weed densities and may interact with herbicide rates and chemistries, so a variable rate of soil-applied herbicide can be applied according to soil type. To acomplish this, on-the-go tools have been developed to measure different soil textures while driving across a field," she said.
Another up-and-coming technology is the WeedSeeker (registered trademark) Automatic Spot Spray System from NTech Industries, Inc. (http://www.ntechindustries.com). This is also an on-the-go machine, connected to a hooded sprayer, Dille said. When a weed passes through an optical sensor under the hood, it prompts the nozzles to spray the herbicide.
Eventually, the weed specialist said, satellite sensing could determine weed patterns and densities in the field. Satellite measurements create a color signature for weeds, which could help with mapping challenges.
In addition to spraying, narrowing rows and/or increasing the crop seeding rate in weed-prone areas could also prove to be effective weed control measures.
"Dense crop planting in weedy areas could choke and shade out weeds," Dille said. In that way, variable-rate planters could be used for site-specific weed management.