Theses and Dissertations

Issuing Body

Mississippi State University


Shaw, R. David

Committee Member

Koger, H. John

Committee Member

Byrd, D. John

Committee Member

Madsen, D. John

Committee Member

Newman, E. Michael

Date of Degree


Document Type

Dissertation - Open Access


Weed Science

Degree Name

Doctor of Philosophy


College of Agriculture and Life Sciences


Department of Plant and Soil Sciences


A survey was conducted by phone to nearly 1,200 growers in six states (Illinois, Indiana, Iowa, Mississippi, Nebraska, and North Carolina) in 2005. The survey measured producers’ cropping history, perception of glyphosate-resistant (GR) weeds, past and present weed pressure, tillage practices, and herbicide use as affected by the adoption of GR crops. The objectives of this study were to determine the effect of GR crop use on producers’ tillage practices; changes in herbicide use patterns after adoption of a GR crop; effect of grower awareness of GR weeds on sources of information growers’ use; and growers’ perceptions on resistance management based on knowledge of GR weeds in their farming operation. The adoption of GR cropping systems contributed to large increases in the percentage of growers using no-till and reduced-till systems. Tillage intensity declined more in continuous GR cotton and GR soybean (45 and 23%, respectively) than in rotations that included GR corn or non-GR crops. Tillage intensity declined more in the states of Mississippi and North Carolina than in the other states, with 33% of the growers in these states shifting to more conservative tillage practices after the adoption of a GR crop. This was in part due to the lower amount of conservation tillage adoption in these states prior to GR crop availability. With respect to herbicide use patterns, frequently used herbicides for fall applications were 2,4-D and glyphosate; these herbicides were often used for preplant, burndown weed control in the spring. As expected, crop rotations using GR crops had a high percentage of respondents that made one to three POST applications of glyphosate per year. Overall, glyphosate use has continued to increase, with concomitant decreases in utilization of other herbicides. Concerning grower awareness of GR weeds and perceptions of resistance management in 2005, the majority of the growers (88%) were aware of a weed’s potential to develop resistance to glyphosate, while 44% were aware of state-specific, documented cases of glyphosate weed resistance. Growers that have had experience with GR weeds were more knowledgeable about resistance management practices that could be used to mitigate them.



grower survey. resistance management||glyphosate-resistance