Date of Award
Master of Science
Crop Production and Physiology
The commercialization of 2,4-D- and dicamba-tolerant trait seed technologies will alter how producers utilize auxinic herbicides. The purpose of this research is to evaluate the current recommended pesticide cleanout procedures for removing auxinic herbicides from two types of spray tanks, identify if increased incubation time of auxinic herbicides in spray tanks increases residue amounts after cleanout, and how soybean growth and yield is impacted by reduced rates of auxinic herbicides similar to those that might occur with ineffective tank clean-out procedures. High-density polyethylene pesticide tanks retained higher amounts of auxinic herbicide residues when compared to stainless steel tanks. Increasing the number of times a pesticide tank is cleaned reduced residues of both 2,4-D choline and dicamba. When current manufacturer-recommended spray tank cleanout procedures were utilized, 2,4-D choline residue amounts were lower than dicamba amounts regardless of tank material type. Analytical laboratory data from the auxinic herbicide incubation experiment showed 2,4-D choline residue amounts in high-density polyethylene decreased over time while residue levels in stainless steel tanks remained steady over all incubation time periods. Retained dicamba residues increased over time in high-density polyethylene tanks while dicamba residue amount remained steady over time in stainless steel tanks. Overall, 2,4-D choline residue levels were lower than dicamba residues in both tank material types. Soybean had a higher tolerance to 2,4-D than dicamba across all soybean injury evaluation timings. Mature soybean height was impacted more by dicamba than 2,4-D. Soybean yield loss was greater for soybeans treated with dicamba than 2,4-D, and much lower rates of dicamba caused soybean yield loss when compared to 2,4-D. Proper cleanout procedures after the use of auxinic herbicide minimized herbicide residue retention in pesticide application tanks. Extended incubation of auxinic herbicides in spray tanks should not increase auxinic herbicide residue levels when proper cleanout procedures are used. Due to higher sensitivity of soybeans to dicamba than 2,4-D, low amounts of dicamba residues remaining in pesticide application tanks could lead to soybean injury, height reduction and yield loss
Kevin Ross Mcgregor
Mcgregor, Kevin Ross, "Auxinic herbicide residue impact on soybean [Glycine max (L.) merr.] growth and yield" (2018). Graduate Theses and Dissertations. 16407.