Control of acetolactate synthase inhibitor/glyphosate-resistant Palmer amaranth (Amaranthus palmeri) in isoxaflutole/glufosinate/glyphosate-resistant soybean

Palmer amaranth is the most problematic and troublesome weed in agronomic cropping systems in the United States. Acetolactate synthase (ALS) inhibitor and glyphosate-resistant (GR) Palmer amaranth has been confirmed in Nebraska and it is widespread in several counties. Soybean resistant to isoxaflutole/glufosinate/glyphosate has been developed that provides additional herbicide site of action for control of herbicide-resistant weeds. The objectives of this study were to evaluate herbicide programs for control of ALS inhibitor/GR Palmer amaranth and their effect on Palmer amaranth density and biomass, as well as soybean injury and yield in isoxaflutole/glufosinate/glyphosate-resistant soybean. Field experiments were conducted in a grower\u27s field infested with ALS inhibitor and GR Palmer amaranth near Carleton, Nebraska, in 2018 and 2019. Isoxaflutole applied alone or mixed with sulfentrazone/pyroxasulfone, flumioxazin/pyroxasulfone, or imazethapyr/saflufenacil/pyroxasulfone provided similar control (86%-99%) of Palmer amaranth 21 d after PRE (DAPRE). At 14 d after early-POST (DAEPOST), isoxaflutole applied PRE and PRE followed by (fb) POST controlled Palmer amaranth by 10% to 63% compared to 75% to 96% control with glufosinate applied EPOST in both years. A PRE herbicide fb glufosinate controlled Palmer amaranth 80% to 99% 21 d after late-POST (DALPOST) in 2018, and reduced density 89% to 100% in 2018 and 58% to 100% in 2019 at 14 DAEPOST. No soybean injury was observed from any of the herbicide programs tested in this study. Soybean yield in 2019 was relatively higher due to higher precipitation compared with 2018 with generally no differences between herbicide programs. This research indicates that herbicide programs are available for effective control of ALS inhibitor/GR Palmer amaranth in isoxaflutole/glufosinate/glyphosate-resistant soybean

Evaluating Evapotranspiration and Management of Glyphosate-Resistant Palmer amaranth (\u3ci\u3eAmaranthus palmeri\u3c/i\u3e S. Watson)

Palmer amaranth (PA) is the most problematic weed in agronomic cropping systems in the United States. Acetolactate synthase (ALS) inhibitor-/glyphosate-resistant (GR) PA has been confirmed in Nebraska and is widespread in several counties. Soybean resistant to isoxaflutole/glufosinate/glyphosate has been developed to provide additional herbicide sites of action for control of herbicide-resistant weeds. The objectives of this study were to evaluate herbicide programs for control of ALS inhibitor/GR PA and their effect on PA density and biomass, as well as soybean injury and yield in isoxaflutole/glufosinate/glyphosate-resistant soybean. A PRE herbicide fb glufosinate controlled PA 80%–99% 21 d after late-POST in 2018 and reduced density 89%–100% in 2018 and 58%–100% in 2019 at 14 d after early-POST. Weed-crop competition models offer a significant tool for understanding and predicting crop yield losses due to crop-weed interference. Within current empirical models, weed biological characteristics are unknown, which limits understanding of weed growth in competition with crops and how that competition affects crop growth parameters. The objective of this study was to determine the effect of center-pivot and subsurface drip irrigation on the average evapotranspiration (ETa) of PA grown in corn, soybean, and fallow in south central Nebraska. Results suggest irrigation affects subplot ETa differences early in the growing season, but crop system and progression of plant growth with available water have a greater effect on ETa differences than irrigation type later in the growing season. Thus, crop management will likely have greater effects on PA ETa values than irrigation practices alone. This study provides base data on weed evapotranspiration and its relation to weed morphological features for future use in mechanistic weed-crop competition models.Velvetleaf is another troublesome broadleaf weed that competes with agronomic crops for resources such as soil moisture. The objective of this study was to determine the effect of degree of water stress on the growth and fecundity of velvetleaf using soil moisture sensors under greenhouse conditions. The results of this study demonstrate that velvetleaf can survive ≥ 50% field capacity (FC) continuous water stress conditions, although with reduced leaf number, plant height, and growth index compared to 75% and 100% FC. Advisors: Amit J. Jhala, Suat Irma