Updated October 3, 2025:
Two small-plot field trials were established at the Ashland Bottoms Experiment Field near Manhattan, KS in May and June of 2024 to evaluate control of large (12" to 15") Palmer amaranth by
2,4-D and Enlist applied in various combinations, sequences, application intervals, and environmental conditions. In the first experiment, initial results suggest that acceptable Palmer amaranth control can be achieved when two applications are made, regardless of herbicide combination, sequence, or application interval. However, single applications provided less control of Palmer amaranth. Soybean yield was similar for all treatments. These results were presented as a poster at the North Central Weed Science Society meeting in December 2024. In the second experiment, results suggest that applications made using 20 GPA provided more consistent control of large Palmer amaranth, although the differences were not statistically significant. This trial also suggests that Delta T is an suitable predictor of weed control, with delta T greater than 5 C resulting in less than 90% weed control, and delta T less greater than 8 C resulting in less than 75% weed control. Both experiments have been repeated in 2025 at Ashland Bottoms and Hays (FY26 funds).
The susceptibility of pigweed samples from 25 soybean fields were screened in greenhouse evaluations during January to March of 2025. Glufosinate (Liberty), 2,4-D, dicamba, and flumioxazin (Valor) were sprayed at typical use rates when pigweeds were 4" to 6" tall and monitored for 4 weeks. Two waterhemp populations, one from CK and one from JF county had over 60% survivors following glufosinate applications. Information about these populations is being shared with the registrant and will be investigated further. Seven additional populations (five waterhemp and two Palmer amaranth) had 30 to 59% survivors; populations from these locations will be screened again in the next two to three years. Two waterhemp and three Palmer amaranth populations had 30 to 59% survivors following 2,4-D application. These locations will be monitored again in the future as well. No populations had 30% or more survivors following dicamba application. However, at least one plant in each population survived application of at least one herbicide. These results well be presented as a poster at the North Central Weed Science meeting in December 2025 and incorporated into Extension presentations during the winter of 2025/2026.
Two small-plot field trials were established at the Ashland Bottoms Experiment Field near Manhattan, KS in May and June of 2024 to evaluate control of large (12" to 15") Palmer amaranth by
2,4-D and Enlist applied in various combinations, sequences, application intervals, and environmental conditions. In the first experiment, initial results suggest that acceptable Palmer amaranth control can be achieved when two applications are made, regardless of herbicide combination, sequence, or application interval. However, single applications provided less control of Palmer amaranth. Soybean yield was similar for all treatments. In the second experiment, results suggest that applications made using 20 GPA provided more consistent control of large Palmer amaranth, although the differences were not statistically significant. This trial also suggests that Delta T is an suitable predictor of weed control, with delta T greater than 5 C resulting in less than 90% weed control, and delta T less greater than 8 C resulting in less than 75% weed control.
The susceptibility of pigweed samples from 25 soybean fields were screened in greenhouse evaluations during January to March of 2025. Glufosinate (Liberty), 2,4-D, dicamba, and flumioxazin (Valor) were sprayed at typical use rates when pigweeds were 4" to 6" tall and monitored for 4 weeks. Two waterhemp populations, one from CK and one from JF county had over 60% survivors following glufosinate applications. Information about these populations is being shared with the registrant and will be investigated further. Seven additional populations (five waterhemp and two Palmer amaranth) had 30 to 59% survivors. Two waterhemp and three Palmer amaranth populations had 30 to 59% survivors following 2,4-D application. No populations had 30% or more survivors following dicamba application. However, at least one plant in each population survived application of at least one herbicide; several populations and 10 to 20% survivors of more that one herbicide.