FirstAct for Efficacy in ACCase-Tolerant Grain Sorghum FirstAct for Efficacy in ACCase-Tolerant Grain Sorghum

The objective of this study was to compare FirstAct with several tank mix partners for efficacy in herbicide-tolerant grain sorghum. FirstAct (quizalofop) alone or in tank mixtures controlled Johnsongrass 94% or more. However, tank mixing FirstAct with any broadleaf herbicide was generally antagonistic to Palmer amaranth control. Minor sorghum injury was 5% or less by four weeks after postemergence treatment. Sorghum yields increased with all postemergence treatments except with atrazine alone.


Introduction
Postemergence grass control in grain sorghum is currently limited to very few herbicides.Consequently, grass weeds that escape a preemergence herbicide can cause severe yield reductions. FirstAct is a grass herbicide that is studied for use in ACCase-tolerant (Double Team) grain sorghum.The objective of this study was to compare FirstAct with several tank mix partners for efficacy in herbicide-tolerant grain sorghum.

Experimental Procedures
An experiment was conducted to compare FirstAct with various tank mix partners for weed control in acetyl CoA carboxylase (ACCase)-tolerant grain sorghum.All herbicides were applied using a tractor-mounted, compressed CO 2 sprayer delivering 19.4 gpa at 30 psi and 4.1 mph.Application, environmental, and weed information are shown in Table 1.Plots were 10 by 35 feet and arranged in a randomized complete block design with four replications.Soil was a Beeler silt loam with 2.4% organic matter and pH of 7.5.Visual weed control estimates were determined on July 27 and August 24, 2021.These dates were 14 and 42 days after the postemergence treatments (DA-B), respectively.Sorghum injury response was visually estimated on July 27, August 10, and August 24, 2021 (14, 28, and 42 DA-B).Yields were determined on November 23, 2021 by mechanically harvesting the center two rows of each plot and adjusting grain weights to 14.0% moisture.

Results and Discussion
FirstAct applied at 10 oz/a applied postemergence controlled Johnsongrass 94% or more regardless of tank mix partner or rating date (Table 2).Conversely, Palmer amaranth control was generally lower with FirstAct tank mixtures compared to Huskie (bromoxynil/pyrasulfotole) plus atrazine or Kochiavore (2,4-D/bromoxynil/ fluroxypyr) alone postemergence.Minor sorghum necrosis and sprawling occurred with FirstAct plus 2,4-D amine or dicamba, and with Kochiavore at 14 DA-B (Table 3).
Visual sorghum injury declined to 5% or less by 42 DA-B.Grain yields increased 34 to 64 bu/a with all postemergence treatments except atrazine alone.The highest yields occurred when FirstAct alone or FirstAct plus dicamba were applied postemergence.

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Figure 2 .
Figure2.Parallel Plus 32 oz/a applied preemergence followed by FirstAct 10 oz/a applied postemergence.Photo taken 28 days after postemergence application.

Figure 3 .
Figure 3. Parallel Plus 32 oz/a applied preemergence followed by FirstAct 10 oz/a plus Huskie 16 oz/a applied postemergence.Photo taken 28 days after postemergence application.

Figure 4 .
Figure 4. Parallel Plus 32 oz/a applied preemergence followed by FirstAct 10 oz/a plus dicamba 8 oz/a applied postemergence.Photo taken 28 days after postemergence application.

Figure 5 .
Figure5.Parallel Plus 32 oz/a applied preemergence followed by atrazine 16 oz/a applied postemergence.Photo taken 28 days after postemergence application.

Table 1 .
Application, environmental, and weed data for the ACCase-tolerant sorghum trial in Kansas Kansas State University Agricultural Experiment Station and Cooperative Extension Service

Table 2 .
Weed control in the FirstAct sorghum study

Table 3 .
Crop response to FirstAct in the ACCase-tolerant sorghum study