Recent data from the Agricultural Resource Management Survey (ARMS) suggest that glyphosate resistant weeds are more prevalent in soybean than in corn production. Glyphosate, known by many trade names (including Roundup), has been the most widely used pesticide in the United States since 2001.
It effectively controls many weed species and generally costs less than the herbicides it replaced. Overall, glyphosate was used on a higher proportion of soybean than corn acres, and it was used alone (not in combination with other herbicides) on a substantially higher proportion of soybean acres.
Using glyphosate alone contributes to resistance. Many soybean fields are managed with glyphosate alone, because the next best alternative herbicides are more expensive, less effective, and/or can cause significant injury to soybean plants.
Source:usda.gov