Interested Members of the University Community are invited to attend the Final Oral Examination for the Degree of Master of Science of Andrew Laplante of the Department of Plant Agriculture

Date: Monday, October 3, 2022
Time: 9:00 AM
Location: Room 307 Crop Science Building

Thesis Title: “Factors Influencing Soybean Tolerance to Diflufenican”

Advisory Committee
Dr. François Tardif, Advisor
Dr. Darren Robinson
Mr. Allan Kaastra

Examination Committee
Dr. Manish Raizada, Chair
Dr. François Tardif
Dr. Darren Robinson
Dr. Peter Sikkema

ABSTRACT

Diflufenican (DFF) is a selective contact and residual herbicide under development by Bayer Crop Science for use in corn and soybean. It represents an under-utilized mode of action (Group 12) and is a novel active ingredient for field crop production in North America. DFF is highly selective on Amaranthus spp., and its registration is intended to target these species and be an important tool to slow the evolution and impact of herbicide resistant weeds. Throughout the initial field testing, differences in soybean tolerance to DFF were observed at several field locations. It was thought that cultivar selection, cultural practices, and environmental conditions may all influence tolerance. Field and growth room studies were conducted to determine whether: 1) soybean cultivars demonstrate differential tolerance to DFF; 2) cultural practices can be manipulated to influence soybean tolerance to DFF; 3) significant rainfall events influence phytotoxicity by splashing herbicide on soybean seedlings. Results indicate that no differences in tolerance exist among soybean cultivars. Instead, it is thought that physiological differences in growth rate and emergence relative to significant rainfall events generate the observed differences in phytotoxicity among cultivars. The importance of significant rainfall events to DFF activity in soybean was further demonstrated using simulated rainfall within a novel methodology designed to test the rain splash potential of herbicides. Significant phytotoxicity was only observed when simulated rainfall was applied, as opposed to a drip irrigation system. This was also consistent with observations from DFF field trials indicating that rainfall timing and intensity are the predominant factors that determine soybean phytotoxicity following preemergence applications of DFF. Preplant applications of DFF one week prior to planting were able to significantly reduce phytotoxicity and resulted in no yield loss, even at high field doses. By utilizing preplant applications, DFF can be used at a higher field dose to achieve improved Amaranthus control, while also maintaining crop safety.