Annual Bluegrass Control University of Nebraska–Lincoln Turfgrass Science Program | Turf.Unl.Edu Pub

Annual bluegrass control University of Nebraska–Lincoln Turfgrass Science Program | turf.unl.edu Pub. 2010c Pro Series Annual bluegrass (Poa annua) remains as bluegrass after an episode of winterkill, one of the most problematic weeds for golf grub damage, disease, herbicide courses, athletic fields, and irrigated misapplication, etc. So if it seems homelawns. Chemical controls have evolved impossible to control annual bluegrass, over the years and can be effective, but what is the justification for trying it? controlling a grass in a grass is difficult Compared to annual bluegrass, creeping because of similar physiology and lack of bentgrass, Kentucky bluegrass, or tall selectivity in herbicides. Plus annual fescue all have reduced water bluegrass is a formidable weed. Annual requirements, increased flexibility in bluegrass is genetically “plastic” ranging irrigation timing and amount, reduced labor from short-lived annuals to long-lived requirements (less “babysitting” like with perennials and thus easily adapts to almost the shallow-rooted annual bluegrass during any turf management system. Poa annua summer), reduced fungicides inputs, var annua is a true annual, usually a lighter improved and more consistent aesthetics green, has coarser leaves and produces and playability, and reduced threat of massive amounts of seedheads compared winterkill. In many cases, controlling annual to the perennial, Poa annua var reptans. bluegrass is easily justified. Annual bluegrass is one of the most Controlling annual bluegrass starts with widespread plants in the world and has cultural controls. Chemical controls will only been found from the Arctic Circle to near be effective in the short term without solid the tropics. Viable seeds of annual cultural controls aimed at limiting annual bluegrass near 110 seeds/sq. inch in soil bluegrass reinfestation. Since annual under greens and 70 seeds/sq. inch in bluegrass has been found to germinate in fairways, compared to the typical seeding complete darkness (shaded by the canopy) rate for cool-season grasses of about 12 (McElroy et al., 2004), a dense turf will not seeds/sq in. Most of this seed in greens can prevent germination, but will likely out- germinate almost immediately while about compete the seedling annual bluegrass. 20% of it will persist over a season or more The cultural controls are listed in Table 1 before germinating (Lush, 1988). On the and can be adapted to almost any turf other hand, seed from fairway or rough setting. The rest of this publication focuses height annual bluegrass will not germinate on chemical control of annual bluegrass, for at least 4.5 months unless it is chilled, but assumes that cultural controls are which is a reflection of its variability (Lush already optimized. 1999). Its adaptability has allowed it to survive and thrive in many environments. To effectively control annual bluegrass in Preemergence herbicides golf or sports turf, turf managers will have Preemergence herbicides applied in early to shape the entire management program fall are highly effective on the annual to discourage it. If only one or two biotypes of annual bluegrass, as long as management factors are modified to they are applied in early September prior to discourage annual bluegrass, then one can the germination window (Dernoeden, hope at best for only modest decreases in 1998). The longer lasting herbicides the annual bluegrass population annually. prodiamine, dithiopyr, or pendimethalin will Even when successful at controlling annual work for this, and a second application in bluegrass, a turf area may be just days Nov., Dec., or March may be required to away from a reinfestation of annual insure control of spring-germinating annual

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Annual bluegrass control bluegrass. This second application may not bluegrass cultivars. It may soon be labeled provide season-long crabgrass control, but for use on greens. Turf safety and efficacy a third application of a preemergence of Velocity increases with temperatures herbicide may exceed label over 70F and thus applications should start recommendations and may affect root in late May or June (McCullough and Hart, growth of the desired turf. Therefore, 2006). Though a wide range of application consider using a post emergence herbicide rates and frequency can be effective, two to like quinclorac as needed for crabgrass in four applications two weeks apart are June or July. Bensulide is the only generally most effective on annual preemergence herbicide labeled for greens bluegrass (McDonald et al., 2006). Adding and is limited to a single application per very low rates of Fe and N (0.03 to 0.09 year on greens. lbs/1000 sq ft) to the tankmix will improve turf safety and have no effect on control (McDonald et al., 2006). If it becomes too Postemergence herbicides effective on annual bluegrass, overseeding Three fall applications of Prograss with desired turf can occur two weeks after (ethofumesate) spaced two weeks apart has the final application of Velocity, or Velocity been the industry standard, but it is often can be applied over newly‐seeded creeping inconsistent at rates safe on Kentucky bentgrass two weeks after emergence bluegrass or creeping bentgrass (Rutledge et al., 2010). (Dernoeden and Turner, 1988). Uptake of Prograss is primarily foliar, so inconsistency Syngenta’s newly‐released Tenacity could be caused by poor uptake because of (mesotione) will control annual bluegrass, environmental conditions at or shortly after but it is currently not on the Tenacity label. application (Kohler and Branham, 2002). Three fall applications starting in late We also know that Prograss affects the September and spaced two weeks apart waxes on the annual bluegrass leaves have been most effective in work at Purdue (Kohler, 2003) and thus should be more and Univ. of Illinois, but control can be very effective on open, windy winters. Fall inconsistent (like most annual bluegrass applications are usually most effective, but controls). Tenacity is extremely safe prior to earlier work at UNL showed spring seeding or over new seedlings and will fit in applications also work (Shearman, 1986) nicely during overseeding Kentucky and work in Kentucky showed additional bluegrass into fairways or athletic fields. spring applications following fall Research is currently underway on Tenacity applications improved control (Woosley et and hopefully annual bluegrass will al., 2003). Furthermore, combining fall eventually be listed on the label. Prograss use with season-long paclobutrazol (Trimmit, TGR) applications or Arysta’s amicarbazone is under using the prodiamine in the fall plus three development and we have been working applications of Prograss in the fall improves with it for a number of years with varying control (Rossi, 2001). success. It is currently labeled for rice and thus likely would not be difficult to label in The most recent postemergence herbicide turf. Determining the application season, for annual bluegrass is Velocity (bispyribac‐ rate, and frequency for control of annual sodium) by Valent. Velocity is effective for bluegrass while maintaining safety on controlling annual bluegrass in fairway desired turf is proving difficult. It is too height creeping bentgrass and lawn height early to tell if and when it will be released tall fescue or perennial ryegrass, but is not to the industry. safe on many cultivars of Kentucky

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Annual bluegrass control Growth regulators to force the desired grass into dormancy, Paclobutrazol (Trimmit, TGR) and which should kill the annual bluegrass. flurprimidol (Cutless) selectively inhibit Apply any of the labeled preemergence growth of annual bluegrass while minimally herbicides (other than siduron) and start affecting creeping bentgrass growth. regular irrigation to bring the desired turf Though these growth regulators were out of dormancy. The desired turf should previously recommended only during the recover fairly quickly whereas the summer, recent experience suggests preemergence herbicide will prevent the applications every two or four weeks annual bluegrass from germinating. A throughout the spring, summer, and fall are second application may be needed later in most effective in limiting annual bluegrass the fall or early next spring to maximize while encouraging spread of creeping annual bluegrass control. Since some seed bentgrass (Woosley et al., 2003). will remain viable, continue the late Trinexapac (Primo or T-NEX) will not help to summer preemergence herbicide control annual bluegrass, but will actually application for two to three years or until improve the health and summer annual bluegrass is no longer a problem. performance of the grass. Research from This strategy gets more complicated if the New York on fairways indicates that any annual bluegrass was so dense that annual bluegrass reduction with reseeding is required. If so, start this preemergence herbicides or Prograss is program as early in the summer as possible reversed by using trinexapac (Rossi, 2001) . (early to mid-July if possible), reseed as Trinexapac should not be used in an annual soon as the area enters dormancy (late July bluegrass control program, but is essential or earlier), and start watering immediately in an annual bluegrass to encourage germination of the desired encouragement/management program. turf. The annual bluegrass likely will not Legacy is a combination of flurprimidol and germinate until average air temperatures trinexapac and the flurprimidol controls return to 70F (Kaminski et al., 2007), so a annual bluegrass growth while the preemergence herbicide should be applied trinexapac tends to reduce the off-color as soon as the label allows after emergence expected by flurprimidol. Early data of the desired species. Dithiopyr has the suggests that this combination should still most flexible label for applications over new reduce annual bluegrass spread (Bigelow et seedings. Annual bluegrass in roughs and al., 2007). Mefluidide (Embark) and lawns can also be controlled selectively by ethephon (Proxy, Ethephon) are growth Prograss. Though this product is not regulators that can control annual available to homeowners, it can be used by bluegrass seedheads when applied shortly professionals on residential turf. Generally after green-up of annual bluegrass in the three applications in the fall are most spring. During seedhead production, this effective, but be sure to follow label strategy can improve visual quality of any precautions. turf area as well as increase smoothness of Controlling annual bluegrass in sports putting greens, but it tends to strengthen fields the annual bluegrass allowing it to better Annual bluegrass control in sports fields is survive summer weather (Gaussoin and difficult because the turf is constantly worn, Branham, 1989) opening voids where annual bluegrass can infest. Soil compaction, frequent fertilization, and frequent light watering to Controlling annual bluegrass in roughs encourage germination and establishment and homelawns of regular overseedings further encourages Turn off the irrigation in July and/or August

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Annual bluegrass control annual bluegrass. A late summer control, but be sure to follow label preemergence herbicide and/or Prograss precautions for Prograss use before or after can be used in the fall on spring-use applying growth regulators. Summer baseball fields. On heavily used fall-use applications of Velocity can also fields that require overseeding, perennial aggressively remove annual bluegrass. Start ryegrass can be seeded into a Prograss applications once temperatures are application with no delay or Prograss can regularly higher than 70F in late May or be applied to newly-seeded perennial early June. Multiple applications are ryegrass 2 weeks after emergence. needed every two to four weeks and the However, Prograss is not nearly as safe on rate will be dictated by how aggressively Kentucky bluegrass and seeding must be you want to control the annual bluegrass. delayed at least 6 weeks after the final Applications can be continued into the fall Prograss application, or Prograss can be until desired annual bluegrass reduction is applied to newly-seeded Kentucky bluegrass reached and fall preemergence herbicides 8 weeks after emergence. This virtually should be used to prevent reinfestation. eliminates either fall applications of Multiple years of this strategy will likely be Prograss or fall overseeding of Kentucky needed. bluegrass. However, Kentucky bluegrass Kentucky bluegrass fairways: Growth can be dormant-seeded into fields treated regulators will likely not selectively reduce previously with Prograss with no annual bluegrass in Kentucky bluegrass and consequences. So consider overseeding with Velocity will damage many of the Kentucky perennial ryegrass during the fall as needed bluegrass cultivars. Therefore, fall or to maintain turf density and playability, fall+spring applications of Prograss make three applications of Prograss in combined with fall preemergence herbicides September through October to control is currently the best strategy. Tenacity may annual bluegrass, and then dormant seed be an option in the future for annual with Kentucky bluegrass in November or bluegrass control in Kentucky bluegrass December after the playing season. Fall-use fairways. fields are where Tenacity herbicide may have a good fit because it is safe before or Controlling annual bluegrass in greens after seeding Kentucky bluegrass or Fewer options exist for controlling annual perennial ryegrass, but annual bluegrass is bluegrass on low-mowed greens. A fall currently not on the Tenacity label. application of bensulide will help prevent germination of annual bluegrass, but has

no effect on established plants. Currently Controlling annual bluegrass in fairways there are no postemergence herbicides for Creeping bentgrass fairways: A low impact Poa annua that are labeled for greens. approach uses paclobutrazol or flurprimidol Growth regulators may have the most applied spring, summer, and fall to help potential because they work well at fairway shift the balance in favor of creeping height where the creeping bentgrass can bentgrass over annual bluegrass. Secondly, effectively outgrow the regulated annual an additional preemergence herbicide bluegrass. However, this approach is not application in early Sept and again in well-documented on greens-height turf. The December or March will help limit ability for creeping bentgrass maintained germination. To make this strategy even under the low-mowed greens environment more aggressive, apply Prograss in fall or to outgrow annual bluegrass is greatly fall+spring in addition to the growth reduced compared to fairway height, regulators and preemergence herbicides. regardless of differential growth regulation. This approach may provide complete Much of the research with growth

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Annual bluegrass control regulators used successful on greens was 4. Kaminski, J. E., and P. H. Dernoeden. 2007. done in the Southeast U.S. with tremendous Seasonal Poa annua L. seedling emergence patterns in Maryland. Crop Sci. 47(2):p. pressure from summer weather to help 775‐781. push the balance in favor of the bentgrass 5. Kohler, E. 2003. Taking control: A plan for over annual bluegrass. Furthermore, much attack for Poa. Grounds Maint. 38(4):p. 32‐ of the research on greens was done ten 34, 36. years ago or more when only a few yearly 6. Lush, W.M. 1988. Biology of Poa annua in a temperate zone golf putting green (Agrostis applications were made as opposed to our stoloniferalPoa annua) I. The above‐ground now typical every-other-week applications of population. Journal of Applied Ecology. growth regulators. Practical experience 25:977‐988. suggests that paclobutrazol or flurprimidol 7. Lush, W.M. 1988. Biology of Poa annua in a applied every two weeks during the growing temperate zone golf putting green (Agrostis stoloniferalPoa annua) II. The seed bank. season can reduce annual bluegrass on Journal of Applied Ecology. 25:989‐997. greens, but there is no research data in the 8. Lush, W. M. 1989. Adaptation and upper Midwest to support this. Current differentiation of golf course populations of work at the University of Nebraska, Purdue, annual bluegrass (Poa annua).. Weed Sci. Michigan State, and Kentucky will provide 37(1):p. 54‐59. insight on annual bluegrass control on 9. Lycan, Darren W.; Hart, Stephen E. 2006. Seasonal effects on annual bluegrass (Poa greens with growth regulators or annua) control in creeping bentgrass with herbicides, but preliminary data already bispyribac‐sodium.Weed Technology. July‐ suggest control is inconsistent. September. 20(3): p. 722‐727. 10. McCullough, Patrick E.; Hart, Stephen E. Control of annual bluegrass is difficult at 2006. Temperature influences creeping best. However, a combination of cultural bentgrass (Agrostis stolonifera) and annual and herbicidal practices can be successful bluegrass (Poa annua) response to producing a turf that requires less inputs bispyribac‐sodium. Weed Technology. July‐ September. 20(3): p. 728‐732. and performs more consistently and reliably 11. McDonald, Steven J.; Dernoeden, Peter H.; year around. Kaminski, John E. 2006. Creeping bentgrass tolerance and annual bluegrass control with Authors: bispyribac‐sodium tank‐mixed with iron and Zac Reicher and Roch Gaussoin, nitrogen. Applied Turfgrass Science. August Professors; Department of Agronomy 11. p. [1‐7]. and Horticulture; University of 12. McElroy, J. Scott; Walker, Robert H.; Nebraska‐Lincoln Wehtje, Glenn R.; Van Santen, Edzard. 2004. Annual bluegrass (Poa annua) populations exhibit variation in germination Literature Cited response to temperature, photoperiod, and 1. Bigelow, C. A., Hardebeck, G. A., and fenarimol.Weed Science. January/February. Bunnell, B. T. 2007. Monthly flurprimidol 52(1): p. 47‐52. applications reduce annual bluegrass 13. Rossi, F.S. 2001. Annual bluegrass populations in a creeping bentgrass fairway. population dynamics in response to growth Online. Applied Turfgrass Science regulators and herbicides. International doi:10.1094/ATS‐2007‐0508‐02‐RS. Turfgrass Society Research Journal. 9(Part 2. Dernoeden, P. H. 1998. Use of prodiamine 2): p. 906‐909. as a preemergence herbicide to control 14. Woosley, Paul B.; Williams, David W.; annual bluegrass in Kentucky bluegrass. Powell, A. J. Jr. 2003. Postemergence HortScience. 33(5):p. 845‐846. control of annual bluegrass (Poa annua spp. 3. Gaussoin, R. E., and B. E. Branham. 1989. reptans) in creeping bentgrass (Agrostis Influence of cultural factors on species stolonifera) turf. Weed Technology. dominance in a mixed stand of annual October‐December. 17(4): p. 770‐776. bluegrass/creeping bentgrass.. Crop Sci. 29(2):p. 480‐484.

Annual bluegrass control University of Nebraska–Lincoln Turfgrass Science Program | turf.unl.edu Pub. 2010c Pro Series Table 1. Summary of practices to favor or culturally control annual bluegrass.

Practice To favor annual bluegrass To control annual bluegrass Mowing height Lower the better Higher the mowing height will favor the desired species Irrigation Shallow and frequent irrigation to keep the Keep the area as dry as possible. Allowing upper 1 inch of the soil profile damp for the dormancy of the desired turf should thin or shallow rooted annual bluegrass. kill annual bluegrass. Aerfication Aerification in spring and/or fall to bring Aggressive aerification to minimize seedheads to the surface and encourage compaction. Primarily done in the summer germination when annual bluegrass will not be germinating Nitrogen Spring and fall nitrogen, especially late fall Primarily in summer. Aggressively growing when annual bluegrass is still growing annual bluegrass in spring and fall will aggressively. respond favorable to spring and fall N. Phosphorus Regular phosphorus increases availability to Low phosphorus fertilization in theory limited root system of annual bluegrass and reduces seedhead production. should aid in seed production. Seedhead The growth regulators Embark, Proxy or Constant mowing with clippings caught management Ethephon are most effective seedhead during seedhead production will help long- limiters. Limiting seedheads will conserve term to limit supply in soil. Gaussoin and carbohydrates for better summer and Branham (1988) reported that removing potentially winter survival. These will also clippings can reduce annual bluegrass eventually limit seed stores in the soil. populations up to 20% over three years. Fungicides Regular fungicides targeted for summer Avoid any fungicides that will control patch and anthracnose in addition to the summer patch or anthracnose when typical dollar spot, brown patch, and treating for dollar spot, brown patch, or pythium controls. pythium controls in the desired turf. Preemergence Apply at typical timing to control crabgrass Labor Day applications will minimize annual herbicides and concentration in soil should allow bluegrass germination in fall, and likely will annual bluegrass germination near Labor require a second application again in late Day. fall or very early next spring Postemergence Velocity and Prograss are effective on herbicides mature annual bluegrass. Certainty and a number of others will control young annual bluegrass. Some will try low rates of glyphosate. Tenacity and Arysta’s amicarbazone are still being evaluated for cool-season turf. Growth Trinexpac (Primo, T-Nex) will help improve Paclobutrazol (Trimmit, TGR) or flurprimidol regulators stress tolerance and help to make annual (Cutless, Legacy) will limit growth of annual bluegrass heathier. bluegrass allowing desired turf to out compete annual bluegrass