Weed Control with Single and Split Herbicide Applications in Corn Weed Control with Single and Split Herbicide Applications in Corn

The objective of the study was to compare season-long weed control from single and sequential herbicide applications in corn. Kochia control was 90% or more late in the season, and did not differ among herbicides. All herbicides except Lumax EZ provided 90% or more Russian thistle control by the season’s end. Palmer amaranth control was lowest when Bicep II Magnum was applied preemergence (PRE) and followed by Lexar EZ postemergence (POST), and when Acuron was applied PRE and again POST. Compared to the untreated control, corn receiving herbicide treatments yielded more than three times as much grain, but yields did not differ among herbicides.


Introduction
Early season weed control in corn is critical to prevent competition during crop establishment.Herbicides with residual activity are typically used near planting time to achieve this, but extending the length of residual activity can be accomplished by delaying some of the preemergence herbicide until after the crop emerges.The objective of this study was to compare single preemergence herbicide treatments with sequential split applications for efficacy in corn.

Experimental Procedures
An experiment was conducted at the Kansas State University Southwest Research-Extension Center near Garden City, KS, to evaluate single versus split application of herbicide premixtures (Table 2) for efficacy in corn.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 7.6.Visual estimates of weed control were taken on June 24 and August 14, 2020.These dates were 34 and 85 days after the postemergence treatments (DAB).Corn yields were determined on October 1, 2020, by mechanically harvesting the center two rows of each plot and adjusting grain weights to 15.5% moisture.

Results and Discussion
Early season control of all weed species was 90% or more with all preemergence (PRE) herbicides, and did not differ between treatments (data not shown).Control of common sunflower and green foxtail remained 90% or more throughout the season regardless of herbicide.Bicep II Magnum (S-metolachlor/atrazine) applied PRE followed by Lexar EZ (S-metolachlor/atrazine/mesotrione) POST and Acuron (S-metolachlor/atrazine/mesotrione/bicyclopyrone) applied PRE and POST provided less than 90% kochia and Palmer amaranth control at 34 DAB (Table 2).Kochia control was similar among all herbicides at 85 DAB, but Palmer amaranth control remained less than 90% with the previously mentioned treatments as well as with Bicep II Magnum PRE followed by Halex GT (S-metolachlor/glyphosate/mesotrione) POST.All herbicides controlled Russian thistle similarly at 34 DAB, but Lumax EZ (S-metolachlor/ atrazine/mesotrione) alone PRE was less efficacious than other treatments on Russian thistle at 85 DAB.Grain yields did not differ among herbicide-treated plots.However, yields increased 85 to 104 bu/a with herbicide-treated plots compared to the untreated controls (40.9 bu/a).

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Figure 3 .
Figure3.Lexar EZ at 48 oz/a applied preemergence followed by Acuron at 48 oz/a postemergence.Photo taken 49 days after postemergence application.

Figure 4 .
Figure 4. Bicep II Magnum at 67 oz/a applied preemergence followed by Halex GT at 58 oz/a applied postemergence.Photo taken 49 days after postemergence application.

Figure 5 .
Figure 5. Corvus at 5.6 oz/a plus atrazine at 32 oz/a applied preemergence followed by Harness Max at oz/a plus glyphosate at 32 oz/a applied postemergence.Photo taken 49 days after postemergence application.

Table 1 .
Application, environmental, and weed information for the single and sequential treatment study in corn Kansas State University Agricultural Experiment Station and Cooperative Extension Service

Table 2 .
Weed control and corn yield from the single and sequential treatment study in corn