Effectiveness of late-season bermudagrass removal using herbicide combinations

Effectiveness of late-season bermudagrass removal using herbicide combinations

Figure 1. (a) Plots of 'Midlawn' bermudagrass and (b) plots of common bermudagrass on June 12, 2014 (252 days after application on October 3, 2013) for recovery from fall applications of glyphosate, fluzifob, and mesotrione combinations. All other treatments containing glyphosate (not pictured) had a similar percentage of green cover as the glyphosate plots and plots treated with fluziphob and mesotrione (not pictured) had a similar percentage of green bermudagrass cover as those treated with fluziphob only. (Photos: Jared Howell, Ph.D.)

Multiple summer applications of glyphosate at rates up to 3.75 pounds acid equivalent (ae) per acre-1 Usually recommended for Bermuda plants (Cynodon spp.) control(1,3,5). However, this system results in an extended 3-4 month period of troublesome, non-functional turf, which is not ideal for spring establishment.

Applying glyphosate in the fall before winter dormancy in the southern United States can control bermudagrass and benefit spring establishment projects (2,3). However, researchers have not evaluated this strategy in the Central Plains region.

We wanted to determine parameters for late-season herbicide applications to control bermudagrass as it transitions to dormancy in the Central Plains. Recommendations and previous research support the addition of herbicides such as fluazifop or mesotrione to improve nonselective control of bermudagrass (5)

This trial aims to examine the effectiveness of late-season bermudagrass removal using the herbicide combinations glyphosate, fluzifob, and mesotrione.

Materials and methods

We started experiments on October 3, 2013 in Rocky Ford Turfgrass Research Center In Manhattan, Kansas, on mature hybrid bermudagrass 'Midlawn' and in Stag Hill Golf Course In Manhattan, Kansas, on mature common bermudagrass. At both sites, we maintained research plots (5 × 5 feet) at a mowing height of 3 inches.

Seven herbicide treatments containing glyphosate (GlyphoMate 41, PBI-Gordon Corp.), fluazifop (Fusilade II, Syngenta), and mesotrione (Tenacity 4 SC, Syngenta) were arranged in a completely randomized block design with four replications at each site. The team applied herbicide treatments using carbon dioxide2– Compact boom sprayer equipped with XR TeeJet 8004-VS flat fan nozzles calibrated to deliver 44 gallons per acre-1 At 40 psi.

Image: Table 1We based product application rates (Table 1) on extension recommendations and previous research (2,3,5) and included an untreated control.

We visually estimated green bermudagrass cover (range from 0 to 100 percent) when we initiated treatment and every 14 days after application (DAA) until the bermudagrass was completely clear of green cover (October 31, 2013). Data collection resumed before spring green-up on 2 May 2014, and continued until 25 August 2014 (326 DAA).

We conducted a separate analysis for each site to reduce confounding effects caused by cultivar differences. Data were subjected to analysis of variance (ANOVA) using the GLIMMIX procedure of SAS (SAS 9.3, SAS Institute) with block as a random effect. Means were separated using Fisher's protected LSD test (P < 0.05).

Results and conclusions

All treatments reduced green bermudagrass cover at every site at 14 DAA (Figures 1 and 2), except for mesotrione at Rocky Ford, mesotrione, fluazifop, and a combination of mesotrione and fluazifop at Stagg Hill. However, only treatments containing glyphosate delayed spring greening at each site the following year.

Image: Figure 2

Figure 2 – Percent green cover of 'Midlawn' bermudagrass 14 to 326 days after application (October 17, 2013 to August 25, 2014) at the Rocky Ford Turfgrass Research Center. Different letters on observation dates indicate significant differences at P < 0.05).

Treatments at Rocky Ford resulted in a similar “Midlawn” green cover compared to the untreated control by July 25, 2014 (Figure 1). At Stagg Hill, common bermudagrass treated with glyphosate or mixtures containing glyphosate had significantly lower green cover (≥ 38 percent) at the last classification on August 25, 2014 (Figure 2)

At all taxonomic dates and sites, the addition of mesotrione, fluazifop, or both to glyphosate did not reduce green bermudagrass cover, which differs from previous research (5).

Differences in green bermudagrass cover between cultivars may be due to improved genetics of “Midlawn,” which is known to have improved stand stability and cold tolerance compared to common bermudagrass (4). The reduced cold tolerance of common bermudagrass may have enhanced the effectiveness of glyphosate treatments at Stagg Hill.

Similar to our findings with “Midlawn” bermudagrass at Rocky Ford, other research (2) reported that a single fall application of glyphosate reduced the cover of Tifway hybrid bermudagrass but did not confer complete control.

Image: Figure 3

Figure 3 – Percentage green cover of 'Midlawn' Bermuda grass 14 to 326 days after application (October 17, 2013 to August 25, 2014) at Stagg Hill Golf Course. Different letters on observation dates indicate significant differences at P < 0.05).

Overall, results indicate that applying glyphosate once in the fall before bermudagrass dormancy reduces grass cover the following spring. Treatments with glyphosate resulted in a similar or slightly faster emergence toward winter dormancy when compared to untreated bermudagrass and delayed spring greening.

Adding mesotrione, fluazifop, or both to fall glyphosate applications did not enhance bermudagrass control in our trials. Although we have observed a significant reduction in spring greening, turf managers may need to make additional applications in the spring to increase effectiveness before spring establishment.

More research is needed to improve fall application rates of glyphosate and combine fall and spring applications to more efficiently control bermudagrass.

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