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Use of glyphosate, the active ingredient in a herbicide that can be applied to growing crop plants produced from genetically modified seeds has increased dramatically. The use of glyphosate is a widely accepted weed control alternative, but the genetically modified crops have not been well received in some import markets. In this study, we conducted a multi-year study using an herbicide applicator that sensed the presence of green plant material and applied herbicide to the area where the plant material was located. The herbicide was applied under a hood to reduce weed competition with the crop plants (either corn or soybeans) in the rows adjacent to the hoods. Replicated treatments were conducted to evaluate weed infestation level, the amount of herbicide applied, the level of control achieved, and the plots were harvested at maturity to compare yields. Statistical analysis was used to compare weed control and yields among the plot treatments for each crop.

Postemergence broadcast application of a selective herbicide weed control treatment in corn can be expected to provide a higher level of broadleaf weed control than the under-hood application of the nonselective (glyphosate) herbicide. In soybeans, the relative level of weed control varied among treatments from year to year in response to environmental conditions, timing of application, weed pressure, etc. Yields of both corn and soybeans varied significantly among weed control treatments, but the highest yield was not associated with a particular treatment.

The use of the under-hood sensor-controlled application technology can result in significant savings (up to 80%) in the amount of glyphosate used to control weeds in corn and soybeans in the upper US Cornbelt in a particular year, and over time, can average about 45%. When a preplant incorporated grass herbicide is not included in the weed control program, glyphosate savings will average about 20%, but the cost of the total weed control program is lower than any of the other treatments included in this study, and comparable to the cost of blanket application of glyphosate for weed control in genetically modified corn and soybean crops.