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Key Takeaways

  • Poa annua is problematic in ultradwarf bermudagrass putting greens because the plant characteristics and timing of active growth for the two grasses are so different.
  • Fully eradicating Poa annua from ultradwarf greens is very challenging, so the goal for most courses is to minimize its presence and impact on playability.
  • Pre and postemergence herbicides are part of successful control, but resistance is an issue and herbicides alone cannot solve Poa annua problems.
  • Cultural practices and growing environments that favor dense and healthy ultradwarf greens are a critical part of any Poa annua control strategy.

Poa annua remains one of the most persistent and disruptive weeds in ultradwarf bermudagrass putting greens, particularly throughout the Southeast. From a consulting perspective, it is less a question of whether Poa annua will be an issue and more a matter of how well it is managed within the system. Its biological advantages, rapid germination, prolific seed production and adaptability to low mowing heights make it uniquely suited to exploit weaknesses in bermudagrass stands, especially during seasonal transitions.

The primary issue Poa annua presents is inconsistency. Bermudagrass and Poa annua differ significantly in growth habit, color, leaf texture and seasonal performance. These differences manifest most noticeably on the putting surface, where uniformity is paramount. Poa annua tends to produce a lighter green color and a more upright growth habit, creating a mottled appearance that is often unacceptable to golfers. The differences in growth habit and timing of optimal growth also lead to bumpy surfaces, especially when Poa annua is growing actively in shoulder seasons while bermudagrass is growing slowly or is fully dormant. Early spring can be especially problematic in the Southeast because conditions are ideal for Poa annua while bermudagrass is often worn down by winter play. Aggressive Poa annua seedhead production, particularly in late winter and spring, adds to the variability in ball roll. Even under intensive management, seedheads can disrupt smoothness and trueness, leading to dissatisfaction among golfers.

Beyond aesthetics and playability, Poa annua also introduces agronomic challenges. It is inherently less heat and drought tolerant than bermudagrass. As temperatures rise in late spring and early summer, Poa annua often declines rapidly, leaving voids in the putting surface. This decline is typically accelerated by disease pressure during hot, wet and humid conditions, as stressed Poa annua becomes highly susceptible to pathogens. The resulting voids reduce surface uniformity and create opportunities for further weed encroachment.

Another agronomic issue is that when Poa annua is actively growing during cooler weather, ultradwarf bermudagrass greens are growing slowly, if at all. Mowing and/or rolling can help minimize the impact of Poa annua plants on ball roll, but these practices can also increase wear on the desired bermudagrass, which can lead to more opportunities for Poa annua to gain ground. As the population of Poa annua in the putting greens increases, these and other agronomic issues become more challenging to manage, so keeping Poa annua under control as much as possible is the primary goal.

Fertility Program

Achieving this level of surface dominance begins with a carefully balanced fertility program designed to sustain consistent growth without encouraging excessive thatch accumulation or unwanted vertical elongation. Nitrogen applications should be delivered in light, frequent increments to promote steady lateral spread and recovery, rather than flushes of growth that can lead to scalping or increased disease susceptibility. Equally important, potassium should be maintained at adequate levels to enhance plant resilience, particularly in the face of summer stressors such as heat, traffic, and periodic drought.

Elevated soil phosphorus levels have been associated with increased Poa annua populations in closely mown turfgrass environments (Guertal & McElroy, 2018). Excessive phosphorus can provide a competitive advantage to Poa annua, allowing it to establish and persist more readily in putting greens and other intensively managed turf areas. For this reason, phosphorus applications should be guided by soil test results and targeted to maintain levels within agronomically appropriate ranges, thereby promoting the competitiveness of the desired bermudagrass while reducing conditions that may favor Poa annua encroachment.

Rutgers University turfgrass research has noted that elevated soil pH can be associated with increased Poa annua pressure in creeping bentgrass, making pH management an important cultural tool in suppression programs (McNally et al., 2024). Maintaining soil pH in a slightly more acidic range can help strengthen bermudagrass competitiveness and reduce Poa annua populations over time.

Moisture Management

Moisture management is equally critical in tipping the competitive balance toward bermudagrass during the summer months. Excessively wet conditions, whether from overwatering, poor drainage or prolonged rainfall, create an environment highly conducive to Poa annua germination, survival, and eventual reestablishment. In contrast, firm, well-drained surfaces inherently favor bermudagrass by promoting deeper rooting, improved oxygen exchange, and greater heat and traffic stress tolerance.

Superintendents should target a consistently moderate soil moisture profile, carefully balancing the need to prevent drought-induced stress with the equally important goal of avoiding prolonged saturation. This requires a disciplined, responsive irrigation approach, in which water is applied based on plant demand and environmental conditions rather than on fixed schedules. Allowing the surface to dry down between irrigation events not only enhances firmness and playability but also puts Poa annua at a competitive disadvantage, encouraging bermudagrass to expand laterally and occupy available space.

Using portable moisture meters to guide putting green irrigation can significantly improve the precision and effectiveness of this program. By providing real-time, site-specific data, these tools allow superintendents to make informed irrigation decisions that optimize water-use efficiency and maintain optimal rootzone moisture.

Improving surface and subsurface drainage is also an effective part of Poa annua control. Areas of putting greens that tend to gather and hold more water are often where a high amount of Poa annua encroachment is observed during cooler and wetter periods, so any projects that can be done to improve drainage will enhance bermudagrass health and limit the amount of moisture available for Poa annua.

Cultural Practices

Cultural practices during the summer should be intentionally structured to enhance the density and vigor of bermudagrass and actively disrupt the life cycle of Poa annua. Topdressing and aeration are fundamental practices for maintaining healthy ultradwarf greens, and they place Poa annua at a relative disadvantage by limiting the amount of moisture that is held in the upper portion of the putting green rootzone. Incorporating vertical mowing and grooming into the program refines surface quality and triggers new shoot growth for improved density and increased surface smoothness. The frequency, intensity and timing of all cultural practices should be carefully managed to maintain bermudagrass vigor and allow adequate recovery time. Excessive stress weakens the competitive advantage of bermudagrass, creating favorable conditions for Poa annua germination, establishment and long-term persistence.

Slightly raising the mowing height on ultradwarf putting greens heading into fall can help improve Poa annua control by reducing mechanical stress on the turf. Healthier, less-stressed bermudagrass develops greater density and is better able to compete with Poa annua. The additional leaf tissue will also help maintain bermudagrass density and coverage through the winter, when wear can create voids for Poa annua to occupy going into spring.

Minimizing shade on ultradwarf putting greens is another important “cultural practice” that will help minimize Poa annua issues. Bermudagrass requires high light levels to maintain density and vigor, whereas Poa annua can persist under lower light conditions. Trees or surrounding vegetation that intercept sunlight will weaken bermudagrass and create favorable conditions for Poa annua establishment. Increasing sunlight through selective tree pruning or removal can strengthen bermudagrass competitiveness and should be considered an important component of any long-term Poa annua management program.

Herbicides

While routine maintenance practices that support bermudagrass health form the foundation of Poa annua control, a well-structured herbicide program is essential for long-term success. Preemergence herbicides are the cornerstone of this approach. Applications should be timed to coincide with declining soil temperatures in late summer and early fall, typically when temperatures at the 2-inch depth consistently fall below 70 degrees Fahrenheit. Poa annua emergence typically occurs when 24-hour mean soil temperatures are sustained at or below 66 degrees Fahrenheit (Taylor et al., 2021). Application timing is critical; Treatments made too early may break down before peak germination, while those made too late will fail to provide effective control.

Sequential applications will be required to sustain an effective chemical barrier throughout the shoulder seasons when Poa annua can most easily invade ultradwarf putting greens. Once soil temperatures are below 66 degrees Fahrenheit, applications should deliver both pre and postemergence control from varying mode-of-action groups.

Advanced management programs frequently incorporate tank-mixing and rotational sequencing of multiple herbicide modes of action across the pre and postemergence spectrum. For example, the preemergence herbicide methiozolin (PoaCure) can be alternated with pronamide (Kerb) to balance soil residual activity, while herbicides such as amicarbazone (Xonerate) and flazasulfuron (Katana) can offer postemergence activity. Some turfgrass managers have expressed curiosity about herbicides that may be effective for controlling Poa annua but are not labeled for use on putting greens. In fact, some of these products have been studied for Poa annua control on ultradwarf greens in research settings for this reason. It is important to remember that research putting greens are not subjected to many of the stressors commonly found on golf courses, primarily traffic and shade. Additionally, the herbicide label is the law when it comes to any application.

Many courses throughout the Southeast are plagued with herbicide-resistant Poa annua on putting greens, particularly populations that are not controlled with Group 2 herbicides such as foramsulfuron (Revolver). From a resistance management standpoint, rotating herbicides across distinct sites of action is not optional; it is essential. Repeated reliance on a single mode of action, particularly within ALS-inhibiting chemistries, has contributed to documented cases of resistance in Poa annua populations. A diversified, programmatic approach that integrates multiple chemistries not only improves short-term control but also preserves long-term herbicide efficacy.

To expand the modes of action available for Poa annua control, some superintendents have considered or applied nonselective herbicides to dormant ultradwarf putting greens where this use is not explicitly prohibited by the product label. This type of application carries substantial risk, it is not recommended by the authors of this article, and we do not believe it should be considered a viable management option. Although bermudagrass may appear fully dormant, herbicides can still translocate to the crowns and roots, increasing the risk of turf injury, delayed spring greenup, and reduced recovery. Any use of nonselective herbicides should be evaluated carefully based on product label requirements, turfgrass condition, environmental conditions, and the potential impact on spring transition.

Successful implementation of an herbicide program to control Poa annua requires precise attention to turfgrass tolerance, environmental conditions and product label guidance and restrictions. Ultradwarf bermudagrass exhibits variable sensitivity to many postemergence chemistries, particularly when it is under stress or during spring transition. Applications made during periods of fluctuating temperatures, low carbohydrate reserves, or reduced growth can result in chlorosis, thinning or delayed recovery from dormancy. As such, rate selection, application interval and environmental timing must be carefully calibrated to balance effective Poa annua suppression with acceptable levels of bermudagrass safety.

Managing the Presence of Poa annua

Despite best efforts, many facilities will continue to contend with significant Poa annua populations in their ultradwarf greens, particularly during the fall, winter and early spring. In these situations, the focus must shift from eradication to minimizing the impact on playability. This requires a thoughtful, integrated approach that addresses both agronomic considerations and golfer expectations.

During the cooler months, Poa annua will become more pronounced on putting surfaces. Mowing and rolling are essential for controlling its vertical growth and maintaining smoothness, but there must be a balance between managing the impact of Poa annua on playability and wearing down the desired bermudagrass that is growing slowly or not at all. Rolling can help mitigate the impact of seedheads and improve ball roll consistency without placing as much additional stress on the bermudagrass as mowing would, but excessive rolling during periods of slow bermudagrass growth can lead to turf thinning, particularly around putting green edges, which can lead to more Poa annua becoming established.

When Poa annua populations are still scattered and individual plants are small, hand removal can be one of the most practical and precise tools available. While this process is labor intensive, physically removing isolated plants before they expand or produce seed can help protect surface uniformity without potentially weakening the bermudagrass base with herbicide applications. The key is timing. Plants should be removed by the roots while they are small enough to leave only minimal disruption to the surface, followed by careful repair so the surrounding bermudagrass can quickly knit back into the void.

Bermudagrass is uniquely adapted to tolerate and respond favorably to frequent, low mowing during periods of active growth when supported by adequate fertility and moisture. Under these conditions, the turf exhibits improved density, finer texture and greater resiliency to traffic and environmental stress when mowed lower. On the other hand, Poa annua is less tolerant of sustained low mowing heights as temperatures rise and environmental pressures increase. As bermudagrass growing conditions improve, frequent low mowing further weakens Poa annua plants and reduces seedhead production.

Superintendents should capitalize on this opportunity in late spring and early summer by implementing mowing practices that promote bermudagrass performance without overextending the plant. This includes maintaining sharp, well-adjusted equipment to ensure clean cuts and avoiding abrupt mowing height changes that could induce stress.

Transition Back to Bermudagrass

As temperatures begin to rise in spring, the transition back to bermudagrass dominance presents both challenges and opportunities. This is often the most volatile period for putting green performance, as declining Poa annua and emerging bermudagrass compete for space. Patience and restraint are essential during this time. Aggressive practices aimed at removing Poa annua too quickly can lead to unacceptable surface disruption, while insufficient management may delay bermudagrass recovery.

Gradual adjustments in cultural practices such as verticutting and topdressing, can facilitate a smoother transition. Increasing nitrogen inputs to favor bermudagrass, combined with strategic aeration and topdressing, can accelerate recovery from winter and encourage the bermudagrass to fill voids left by declining Poa annua. Continued use of plant growth regulators may be warranted to suppress any remaining Poa annua populations and maintain surface consistency.

“There is no single solution, and success is rarely defined by complete eradication.”

Conclusion

Communicating with stakeholders is also a key component of successful Poa annua management. Golfers must understand the challenges of maintaining ultradwarf bermudagrass putting greens in regions with high Poa annua pressure. Setting realistic expectations and providing clear explanations of management strategies can go a long way in fostering support and reducing frustration during transitional periods.

Ultimately, managing Poa annua in ultradwarf putting greens is a year-round endeavor that requires a proactive, integrated approach. There is no single solution, and success is rarely defined by complete eradication. Instead, the goal is to minimize impact on playability and aesthetics while promoting the long-term health and dominance of bermudagrass.

Superintendents who embrace this philosophy by combining sound agronomic practices with strategic chemical inputs and effective communication will be best positioned to navigate the challenges Poa annua presents. While it may never be fully eliminated, the influence of Poa annua can be managed to a level that allows for consistently high-quality putting surfaces, even under the most demanding conditions.

References

Guertal, E.A., & McElroy, J.S. (2018). Soil type and phosphorus fertilization affect Poa annua growth and seedhead production. Agronomy Journal, 110(6), 2165-2170. https://doi.org/10.2134/agronj2018.02.0139

McNally, B.C., Elmore, M.T., Murphy, J.A., & Murphy, S.L. (2024). Annual bluegrass and creeping bentgrass tiller response to phosphate fertilizer and soil pH. Crop Science, 64, 511-522. https://doi.org/10.1002/csc2.21144

Taylor, D.R., Prorock, M., Horvath, B.J., & Brosnan, J.T. (2021). Modeling seasonal emergence of Poa annua in urban greenspace. Scientific Reports, 11, 18960. https://doi.org/10.1038/s41598-021-98525-4