By Scout Nelson
Farmers often work long hours to complete field operations, but new research suggests that stopping herbicide spraying before nighttime may improve weed control. A study at South Dakota State University compared herbicide applications made at 12:00 p.m. and 9:00 p.m. to measure how the time of day affects weed control in soybean fields. The results continued to show that daytime spraying provides stronger weed control than nighttime applications.
Eric Jones, Assistant Professor and SDSU Extension Weed Management Specialist, along with Eric Jones, Philip Rozeboom, Jill Alms, and David Vos, conducted the research to evaluate the performance of Enlist One (2,4-D choline) and Liberty (glufosinate) when applied alone or in a tank mix. The research, repeated in 2026, confirmed for the third consecutive year that herbicides applied at 12:00 p.m. cause greater weed injury than applications made at 9:00 p.m.
During the study, Enlist One was applied at 32 fluid ounces per acre, while Liberty was applied at 43 fluid ounces per acre, along with 3 pounds of ammonium sulfate per acre using 20 gallons of spray solution per acre. Seven days after treatment on June 26, 2026, researchers again observed that weeds treated during the day showed much greater damage than those sprayed at night.
Researchers explained that field conditions often make it difficult for farmers to spray at the ideal time. Wind, rainfall, high temperatures, and equipment problems may delay fieldwork. As a result, many producers continue spraying later in the day to finish the job while weather conditions remain favorable.
The study reminds farmers that extending spraying into the night may reduce herbicide performance by as much as 20%, based on findings collected over the past three years. Some herbicide labels, including Liberty, also require applications to stop before sunset.
Photo Credit: istock-sandramatic
Categories: South Dakota, Crops, Soybeans