Controlling annual bluegrass where the buffalo roam

By |  November 9, 2017 0 Comments

Annual bluegrass (Poa annua L.) control has been thoroughly researched in cool-season turf east of the Mississippi River, but little research has been done in the northern Great Plains. Growing conditions, weather, desired species, as well as biotypes of annual bluegrass change dramatically as one moves west across the United States.

Because previous research and practical experience show that annual bluegrass response to herbicides varies widely among environments and/or biotypes, our objective was to evaluate the efficacy of herbicide programs for annual bluegrass control on fairways in Nebraska. We conducted two 3-year studies at Firethorn Golf Club in Lincoln, Neb., and Omaha (Neb.) Country Club.

A little background

In Nebraska and farther west, fairways mostly are Kentucky bluegrass (Poa pratensis L.), and in some areas this is overseeded with perennial ryegrass (Lolium perenne L.) after summer damage. Annual bluegrass control hasn’t been thoroughly researched in Kentucky bluegrass fairways. Researchers have shown that Tenacity (mesotrione, Syngenta) has potential as a postemergence herbicide to control emerged annual bluegrass. However, Tenacity’s label does not specifically list postemergence control of annual bluegrass. However, it is labeled for preemergence suppression of annual bluegrass and for use on Kentucky bluegrass fairways.

Work in Indiana and Illinois indicated that optimum annual bluegrass control in the fall resulted from three applications of Tenacity at 3 or 5 fl. oz./acre/applied at 14-day intervals, starting in mid- to late September. Three fall applications of Prograss (ethofumesate, Bayer) has been the standard for controlling annual bluegrass in Kentucky bluegrass and/or perennial ryegrass fairways.

Some fairways in Nebraska and farther west are creeping bentgrass (Agrostis stolonifera L.). In creeping bentgrass, Velocity (bispyribac-sodium, Valent) currently is the industry standard for postemergence annual bluegrass control and has been thoroughly researched. Multiple applications on 2- to 3-week intervals are highly effective for annual bluegrass control, and Velocity becomes more effective on annual bluegrass and less phytotoxic on creeping bentgrass at temperatures above 68 degrees F. Current label recommendation for Velocity 17.6WSP is up to four applications at 6 fl. oz./acre applied at 21-day intervals on fairways with relatively low populations of annual bluegrass. Unfortunately, the status of Velocity currently is questionable as Valent is reassessing the herbicide in the turf market. Hopefully, Velocity will remain a viable option for superintendents.

How we did it

Kentucky bluegrass fairways
The Kentucky bluegrass study was located at Firethorn Golf Club and used a low-mow Kentucky bluegrass blend (NuDestiny, Everglade, 4 Season, Solar Eclipse and Beyond) seeded in 2009. Soil type was Aksarben silty clay loam, and maintenance included mowing three times per week at 0.50 inch with clippings returned, 2 lbs. nitrogen (N)/1,000 sq. ft./year, preventative white grub control and Dimension (dithiopyr, Dow AgroSciences) applied in spring for crabgrass control. The Kentucky bluegrass study consisted of 11 late-summer and fall treatments, including combinations of herbicides applied as preemergence Barricade 65WDG (prodiamine, Syngenta) or Tenacity and/or postemergence (Tenacity or Prograss 1.5EC) for annual bluegrass control (Table 1). A non-ionic surfactant (Induce, Helena Chemical) was included with all Tenacity applications at 0.25 percent v/v. We applied treatments starting in August 2010, with identical treatments repeated in 2011 and 2012 over the same plots.

Creeping bentgrass fairways
The creeping bentgrass study was located at Omaha Country Club, which has approximately a 5-year-old creeping bentgrass blend (T1, Alpha and Crenshaw). Soil type was a Monona silt loam, and maintenance included mowing three times per week at 0.375 inch, with clippings collected, 2.4 lbs. N/1,000 sq. ft./year, preventative disease and white grub control, and Dimension applied in spring-split applications for crabgrass control. We also topdressed this area four times annually and aerated twice a year with solid tines to a depth of 5 or 8 inches. The creeping bentgrass study was a 2 X 2 X 2 factorial with two rates of Velocity 17.6 WSP (4 fl. oz./acre + 4 fl. oz./acre applied three weeks apart and 6 fl. oz./acre + 6 fl. oz./acre applied three weeks apart), two applications of Velocity (mid-June plus three weeks and mid-June plus three weeks and mid-September plus three weeks) and two levels of preemergence herbicide (none or Dimension 2EW at 24 fl. oz./acre applied early September) (Table 2). This study also included an untreated control and a Dimension-only treatment applied in early September. Treatments were applied in 2011, 2012 and 2013 over the same plots.

Table 2

We recorded annual bluegrass cover prior to the first application and then throughout the study until spring after the last application. Like long-term disease studies in which scientists combine all readings into a single data point called AUDPC (Area Under the Disease Progress Curve), we also combined all of our readings into a single mean as AUPPC (Area Under Percent Poa Curve). We analyzed all data with SAS and separated means with Fisher’s least significant difference (LSD) at P≤ 0.05.

What we found

Kentucky bluegrass fairways
Annual bluegrass in untreated control plots increased from 14 to 25 percent cover during the 3-year experiment, an increase of 85 percent (Table 1). This indicates the need for controlling annual bluegrass early in the life of a fairway, before populations become excessive. No treatment effects were visible until May 2012 (Table 1), which was after the second year of treatments. Record-high summer temperatures in 2012 reduced annual bluegrass cover to zero in all plots by August 2012. These two observations reinforce the usefulness of long-term annual bluegrass studies in climates like the northern Great Plains, with dramatic weather fluctuations that could confound treatment effects.

Three postemergence applications of Tenacity plus preemergence Barricade applied in August or August and November reduced annual bluegrass cover compared to the untreated control in May 2012 and 2013 and August 2013, and reduced final annual bluegrass cover by more than 75 percent since study initiation (Figure 1). These same two treatments also reduced AUPPC by 69 percent to 83 percent compared to the untreated control.

Figure 1 Control of annual bluegrass by preemergence and postemergence herbicide applications in the Kentucky bluegrass experiment in May 2013.

Three postemergence applications of Prograss plus preemergence Barricade applied in August and November also reduced annual bluegrass cover compared to the untreated control in May 2012 and 2013 and August 2013; reduced final annual bluegrass cover by more than 65 percent from study initiation; and reduced AUPPC by 62 percent compared to the untreated control. Even though many other treatments performed similarly, these were the only three to reduce final annual bluegrass cover and AUPPC compared to the untreated control.

Our data reinforce that Tenacity has potential for controlling annual bluegrass in the northern Great Plains of the United States. We likely could have improved efficacy of postemergence applications of Tenacity with more frequent applications at lower rates or by increasing the amount of N applied with or shortly after application. Tenacity applied alone as a preemergence had little effect on annual bluegrass, as Tenacity applied once as a preemergence in August was the only treatment that did not affect annual bluegrass cover at any time during the study (Table 1).

Figure 2 Control of annual bluegrass by postemergence herbicide applications in the creeping bentgrass experiment in May 2013.

Tenacity applied as a preemergence in August and as a pre/postemergence in November reduced annual bluegrass cover compared to the untreated control rated in May 2012, and thus the November application provided some postemergence control. Annual bluegrass on this site appeared to be mostly Poa annua var. annua because it was fairly coarse textured, light green, and a prolific seed producer. However, the annual bluegrass on this site may have included some Poa annua var. reptans, since preemergence applications of Barricade alone were ineffective. This especially was apparent between August 2012, when no annual bluegrass was visible, and May 2013, when up to 24 percent annual bluegrass was present despite one or two applications of Barricade. This also could suggest that smaller (one- to three-leaf stage) plants of annual bluegrass were present below the Kentucky bluegrass canopy on the August 2012 rating date, and were not affected by Barricade.

Creeping bentgrass fairways
Unlike the Kentucky bluegrass study, annual bluegrass cover did not drop precipitously during the record-high temperatures of summer 2012, with cover in the untreated control at 14 percent in October 2012 compared to 22 percent and 20 percent in September 2011 and October 2013, respectively (Table 2). This could be due to irrigation and aggressive fungicide use, or possibly that the annual bluegrass on this area was Poa annua var. reptans. However, annual bluegrass did decline during winter of 2013-14, with only 14 percent annual bluegrass cover in the untreated control in May 2014 compared to 32 percent, 43 percent and 31 percent annual bluegrass cover rated the previous three springs. Desiccation of annual bluegrass was extensive in Nebraska and the northern Great Plains during the winter of 2013-14. This reiterates the importance of long-term annual bluegrass control studies because single-year studies replicated over time or space may dramatically be affected by weather.

Velocity was extremely effective in this study, reducing annual bluegrass cover to less than 5 percent by the end of the study, compared to 14 percent cover in the untreated control (Table 2). Two applications of Velocity in June reduced annual bluegrass cover throughout the study and reduced AUPPC by 60 percent compared to the untreated control. Adding additional September applications further increased annual bluegrass control, reducing annual bluegrass cover on every rating date, final annual bluegrass cover by an additional 13 percent and AUPPC by 45 percent compared to the June-only applications (Table 2). However, there never was an effect of increasing the rate of Velocity from 4 to 6 fl. oz./acre/application, and there was only one rating date (Oct. 2013) where adding a pre-application of Dimension reduced annual bluegrass cover. The lack of preemergence control further suggests that the annual bluegrass on this site was mostly Poa annua var. reptans.

Summary

Three fall postemergence applications of Tenacity plus Barricade applied as a preemergence in August and/or November was effective in controlling annual bluegrass on Kentucky bluegrass fairways. Replacing Tenacity with Prograss also was effective and would be a means of reducing the chances of annual bluegrass developing herbicide resistance by using herbicides with different modes of action. Velocity applied twice two weeks apart at 4 oz./acre in June was effective for controlling annual bluegrass in creeping bentgrass fairways. Control was improved by adding two additional applications of Velocity in September, but there was no benefit in using the 6 fl. oz./acre rate over the 4 fl. oz./acre rate. Our data confirm that annual bluegrass control research done in other areas of the country is applicable to Nebraska and likely the rest of the northern Great Plains. However, weather extremes in summer or winter in the northern Great Plains may dramatically affect expected annual bluegrass control in any given year.


Acknowledgements
Special thanks to Scott Wilke at Firethorn Golf Club and Eric McPherson at Omaha Country Club for generously allowing us almost unlimited access to their golf courses. Thanks also go to the Nebraska Turf Association for partial funding for this study.

Matt Sousek is manager of the John Seaton Anderson Turfgrass Research Center at the University of Nebraska and can be reached at msousek2@unl.edu for more information. You may obtain the original article from the author or at Reicher, Z., M. Sousek, and M. Giese. 2017. Herbicide Programs for Annual Bluegrass (Poa annua L.) Control in Nebraska. Crop, Forage & Turfgrass Management 2017 3:1-. doi:10.2134/cftm2015.0221

References
Elmore, M. T., J. T. Brosnan, D. A. Kopsell, and G. K. Breeden. 2013. Effects of temperature and nitrogen fertilizer on mesotrione activity against annual bluegrass (Poa annua L.). Int. Turfgrass Soc. Res. J. 12: 657-661.
Reicher, Z. J., D. V. Weisenberger, D. E. Morton, B. E. Branham, and W. Sharp. 2011. Fall applications of mesotrione for annual bluegrass control in Kentucky bluegrass. Appl. Turfgrass Sci.:1-10. doi: 10.1094/ATS-2011-0325-01-RS.
Skelton, J. J., W. Sharp, and B. E. Branham. 2012. Postemergence control of annual bluegrass with mesotrione in Kentucky bluegrass. HortScience 47:522–526.
Woosley, P. B., D. W. Williams, and A. J. Powell. 2003. Postemergence control of annual bluegrass (Poa annua spp. reptans) in creeping bentgrass (Agrostis stolonifera) turf. Weed Technol. 17:770-776.

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