Foxtail Management in Smooth Brome Hay Meadows

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Introduction
Smooth bromegrass (Bromus inermis) is a major hay and pasture crop in eastern Kansas, occupying approximately 1.2 million acres (Figure 1), and yielding up to three tons or greater of dry matter (Lamond et al., 1992) per growing season with good rainfall and adequate fertilization. Since 2007, a perceived or noted decline in smooth bromegrass yield as well as increased foxtail [primarily yellow (Setaria pumila) and giant (S. faberi)] competition in the summer months has been observed. Two field studies in the spring of 2020 evaluated and compared (1) the efficacy of spring and post-harvest applied herbicides, (2) their effect on the smooth bromegrass, and (3) their control of foxtail species in established smooth bromegrass hay meadows.

Procedures
The effects of early spring and post hay harvest applications of pendimethalin (Prowl H2O), S-metolachlor (Dual II Magnum), and metsulfuron (Escort XP) on smooth bromegrass injury, yield, and foxtail and other weed control/suppression were evaluated. Site descriptions and conditions at the time of herbicide application are listed in Table 1. The seven treatments in each experiment were arranged in a randomized complete block design with three replications. Herbicide treatments (Table 2) were applied using a CO 2 backpack sprayer with a 4-nozzle boom with 8002ER nozzles at 35 psi delivering 20 gallons/a of solution. Individual plots were 10-× 25-ft and the treated area was the center 7 × 25 ft of the plot. Crop injury (CI) and foxtail suppression (%) were assessed approximately every 10-14 days after herbicide applications. Two 18-× 18-in. quadrats were clipped from each plot at 3 in. in height on June 5, weighed on an electronic scale, and placed in a dryer at 104°F for 48 hours. Samples were removed and weighed immediately on the same electronic scale. Dry matter percentage was calculated and used to calculate forage dry matter yields/a.

Results
Dry matter yield response trends to treatments were similar, so forage yields from the two sites were combined for analysis ( Figure 2). Foxtail control and brome injury responses were also similar at both locations ( Figure 3). Prowl H2O applied early in the spring resulted in 97% foxtail control, compared to only 47% and 34% control provided by Dual II Magnum and Escort XP, respectively. Post-harvest herbicide applications provided minimal, non-significantly different levels of foxtail control (Figure 3). When data collection ceased in early September, foxtail suppression was unacceptable in all plots (data not shown).
Escort XP applied in early spring (Figure 3) resulted in 28% visual injury to the brome, minimal foxtail control, and 62% less dry matter production compared to the untreated check ( Figure 2). Smooth brome injury was likely exacerbated by below-average temperatures, including six freeze events that occurred the week after spring application (http://mesonet.k-state.edu/).
With the exception of early spring-applied pendimethalin, herbicides did not adequately control foxtail in the short term and caused visible, but not always statistically significant smooth brome injury.
Herbicides did not reduce the late-summer foxtail infestation, despite apparent suppression eight weeks after the early spring application.

Future Research
Based on these results, this work will be repeated in 2021 with refinement of treatments. Prowl H2O will be applied per labeled rates either at greenup or at greenup and after cutting. Smooth bromegrass injury from the Escort XP treatment was unacceptable on cooperators' hay meadows and will be dropped from this study.

Kansas State University Agricultural Experiment Station and Cooperative Extension Service
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