Abstract
AbstractPalmer 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’s 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.
Highlights
Palmer amaranth is a summer annual broadleaf weed belonging to the Amaranthaceae family and is one of dioecious species among pigweeds (Steckel 2007)
Human activities in the 20th century such as agricultural development, within- and between-field operations, and seed and equipment transportation have led Palmer amaranth to spread to the northern United States (Culpepper 2006)
Year-by-treatment interaction for multiple herbicide-resistant (MHR) Palmer amaranth control 21 d after PRE (DAPRE) was not significant (P > 0.05); data were combined for both years, while Palmer amaranth control estimates 14 d after early-POST (DAEPOST) and 28 d after latePOST (DALPOST), Palmer amaranth density, and soybean yield were significant (P < 0.05); data were presented separately for both years
Summary
Palmer amaranth is a summer annual broadleaf weed belonging to the Amaranthaceae family and is one of dioecious species among pigweeds (Steckel 2007). Since the first report of Palmer amaranth in Virginia in 1915 beyond its native habitat in the southwest United States, it has become one of the most problematic and troublesome weeds in agronomic cropping systems in the United States (Culpepper et al 2010). Palmer amaranth is an obligate outcrossing, wild pollinated species (Sosnoskie et al 2012), resulting in wide genetic diversity (Jhala et al 2021; Oliveira et al 2018). In a 2-yr field study in Kansas, Horak and Loughin (2000) reported that Palmer amaranth had the highest plant dry weight, leaf area, water-use efficiency, and growth rate (0.10 to 0.21 cm per growing degree day) compared to redroot pigweed (Amaranthus retroflexus L.), tumble pigweed (Amaranthus albus L.), and waterhemp [Amaranthus tuberculatus (Moq.) Sauer]
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