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Key Takeaways

  • Cyanobacteria, commonly known as blue-green algae, typically fill voids in putting green turf created by other issues.
  • Blue-green algae form mats that inhibit water movement and gas exchange through the rootzone. These mats also make it harder for turf areas to recover vegetatively or with seeding. 
  • The best defense against blue-green algae is to improve growing environments and optimize turfgrass health to minimize voids.
  • If you have blue-green algae on putting greens, a combination of chemical and mechanical control methods is often the most successful management strategy.
  • Reestablishing turf after blue-green algae has taken over an area can be quite difficult. Careful water management is especially important.
     

Cyanobacteria, often referred to as blue-green algae in a golf course setting, is an issue on putting greens that I encounter regularly on my USGA Course Consulting Service visits. Cyanobacteria are photosynthetic bacteria, not true algae, that grow by producing chains of thread-like cells similar to fungi. They thrive in moist putting green soils with elevated organic matter levels and are commonly found in higher pH environments but can be adaptable to many soil conditions. Cyanobacteria are typically observed on putting greens following periods of high stress from a variety of biotic and abiotic factors. This issue is rarely something that comes about on its own; it is almost always a consequence of another turf health issue that creates voids where this group of photosynthetic organisms can thrive. Prolonged wet stretches, high levels of soil organic matter, limited air movement, excessive shade and poor drainage are all potential contributing factors.

Once blue-green algae take hold, they create a crusty layer between the surface and the rootzone. This layer inhibits water infiltration and gas exchange through the soil profile and limits vegetative turf recovery or reestablishment with seed. The presence of this crusty layer and potential clogging of soil pores can cause anaerobic soil conditions that lead to black layer. Blue-green algae can also produce allelopathic substances called cyanotoxins that further inhibit turf growth in and around the affected area (Polyak & Sukharevich, 2025). Research suggests that, in some cases, the blue-green algae can act as a pathogen and directly injure many species of warm- and cool-season turf (Tredway et al., 2006).

From a golfer’s perspective, putting greens with areas of blue-green algae appear inconsistent and ball roll is negatively affected. While there are products that can be used to treat blue-green algae, the problem will return unless underlying turf health issues are also addressed. A holistic approach is needed for lasting success. 

"While there are products that can be used to treat blue-green algae, the problem will return unless underlying turf health issues are also addressed."

Preventive Measures

The best defense against blue-green algae development is improving growing environments, course infrastructure and agronomic programming to support better turfgrass growth and development. Blue-green algae fill voids particularly well in hot and humid environments, so it is a common ailment following wet wilt in the heat of summer or when turf thinning occurs due to environmental or mechanical stress.

Improve growing environments

Optimizing growing environments, especially by improving air movement and increasing the amount of sunlight reaching the surface is vital. In most cases where I observe blue-green algae development, trees located in poor positions are part of the problem. Selective pruning or removal of trees that shade putting greens will help to prevent blue-green algae development. Improving surface drainage by eliminating collar dams and regrading any areas that tend to hold water on the putting surface is imperative for avoiding the wet conditions and turf thinning that create an ideal opportunity for blue-green algae growth. Additionally, installing subsurface drainage infrastructure where necessary can help to promote healthier turf in “push-up” greens that do not already have a subsurface drainage system in place. Regrading areas and installing drainage is temporarily disruptive, but without a long-term solution to drainage issues it is very likely that blue-green algae will return again and again. Even less-disruptive methods of improving drainage like drill-and-fill aeration or slit drainage systems have helped courses reduce the occurrence of cyanobacteria outbreaks.

Increase putting green height of cut (HOC)

Increasing HOC will benefit turf health by promoting photosynthesis, so the turf produces the carbohydrates necessary for growth and development. Research conducted in Wisconsin on creeping bentgrass greens showed that blue-green algae development decreased as mowing height increased from a starting point of 0.110 inch (Stier, 2006). In my experience, adjusting the mowing height up by even 0.005 or 0.010 inch prior to conditions conducive to blue-green algae development can have a positive impact on turf health and minimal impact on playing conditions. Oftentimes this increase in mowing height is only necessary during periods of high stress and can be decreased again once better weather conditions arrive and turf recovery is observed.

Lessen growth regulation from plant growth regulators (PGRs) and DMI fungicides

Managing growth to conserve carbohydrates and improve playability with PGRs must be properly balanced against potential impacts on overall turf health, especially during periods of high stress. It is not easy to properly regulate growth during hot and humid conditions that promote accelerated degradation and shortened efficacy of PGRs without pushing too far and overregulating turf that’s already under environmental stress.

Turf under excessive plant growth regulation during times of stress is unable to grow and recover adequately, which can result in turfgrass decline that creates voids for blue-green algae to inhabit. DMI fungicide applications can also have growth regulating effects at high temperatures and should be used cautiously during periods of summer turf stress. It is important to note that some DMI fungicides released over the last several years don’t have the same regulating properties as older chemistries. Examples include prothioconazole (Densicor), mefentrifluconazole (Maxtima), and flutriafol (Rayora) (Clarke et al., 2024).

Promote water and air movement through the rootzone

A buildup of organic matter at the surface of the putting green rootzone can compromise water infiltration and gas exchange even if the underlying soil properties and drainage infrastructure are well-suited to supporting healthy turf. This leads to turf decline and also creates ideal conditions for blue-green algae because of the additional moisture held at the surface. Aeration, topdressing and other practices designed to dilute and/or remove organic matter all play an important part in preventing the development of blue-green algae. Deferring necessary cultural management practices can lead to a variety of issues in turfgrass health and putting green performance, and the formation of blue-green algae is one example.

Minimize mechanical wear as much as possible

Mechanical wear creates thin areas in the turf canopy that become opportunities for blue-green algae to take over. Common areas where excessive mechanical wear is observed are around the edges of putting greens where rollers typically start and stop, and where the cleanup pass is mowed. Abrupt contours and high-traffic areas where golfers or equipment frequently enter or exit the green are other places where mechanical wear is a common issue.

Some basic steps to minimize wear include varying where the putting green rollers start and stop, and only mowing a cleanup pass every other time the putting greens are mowed. Using a specific mower for cleanup passes throughout the year that is outfitted with smooth front rollers and a higher HOC, usually 0.005 inch higher, is another way to minimize wear around putting green perimeters. Periodically skipping mowing on abrupt putting green contours, or only mowing them in certain directions, and placing hole locations in areas that steer traffic away from stressed turf are other strategies that can help. Tracking putting green performance data can help avoid performing unnecessary practices that add stress but are not needed to achieve playability goals. For example, if clipping yields are low during a stressful period and putting green speed is already within a target range for your facility, forgoing a mow or roll will help limit additional stress on the putting greens.

Be mindful of irrigation practices

Blue-green algae thrive in wet environments, so water management is critical to keep this pest from becoming established. Try to use deep and infrequent irrigation to minimize overly wet surfaces that are more susceptible to blue-green algae development. Also, avoid irrigation timing that will lead to prolonged surface wetness, like late afternoon and early in the evening. Using a portable moisture meter to guide watering decisions and hand watering more often – especially on greens that are susceptible to blue-green algae development – will help. Adjusting sprinkler run times, changing nozzles, and checking to see if any sprinklers around the green inadvertently throw onto the surface can all help to reduce surface wetness and the risk of blue-green algae becoming established.

Controlling Blue-Green Algae

Once blue-green algae become established on putting greens, there are several avenues for control. Typically, the most effective approach is a mix of cultural and chemical measures.

Chemical control

Chlorothalonil is the best chemistry to address blue-green algae populations. Mancozeb also provides control, but it does not work as well as chlorothalonil. Many superintendents use Daconil Zn specifically for algae control, but in a research study it was observed to work similarly to chlorothalonil alone (Clarke et al., 2024). Even though blue-green algae is not a fungus and these products are registered as fungicides with the U.S. EPA, they are effective due to their biocidal effects (Debnath et al., 2012; Tao et al., 2024). Preventative applications are much more effective than a curative approach, so if blue-green algae is a recurring issue and the weather forecast is favorable for development, it’s important to make preventative applications at the label rate for algae on an interval of about seven to 14 days.

Copper hydroxide is also very effective for controlling cyanobacteria but is not nearly as safe for turf as mancozeb and chlorothalonil. Copper hydroxide can be phytotoxic, especially during hot temperatures and when tank-mixed with acidic products. Copper toxicity is also an issue in turf with repeated application. It is not recommended to use copper hydroxide to curatively control cyanobacteria in putting green turf (Clarke et al., 2024).

In one study, preventative phosphite applications every 14 days at the recommended label rate were successful in suppressing algae development (Inguagiato et al., 2017). Potassium phosphite was more effective in preventing cyanobacteria than potassium phosphate (90%-100% suppression compared to 52%-86%). The authors suggest that phosphite uptake by the plant disrupts enzyme activity or metabolization of phosphorus, which restricts cyanobacteria growth. It is important to note that this is not a curative treatment but could be an excellent addition to a plant protectant program if blue-green algae development is common. In this study, preventative applications began in May in Connecticut, which is very similar to the timing of preventative phosphite applications for Pythium.

It's worth mentioning that there are other fungicides, such as fluazinam (Secure), that are labeled for blue-green algae (Table 1). However, research and my experience have shown that chlorothalonil should be your go-to product for dealing with blue-green algae. Some of the other products listed in Table 1 rely more on boosting plant health to fill in voids rather than directly controlling blue-green algae, while others are simply combination products containing chlorothalonil. Additionally, materials like ammonium sulfate and hydrated lime have been used to desiccate or “burn” algae in affected areas. However, these treatments must be used with extreme caution on putting greens because they can also injure turfgrass or contribute to nutrient imbalances if applied improperly.

Cultural control

Using mechanical means to break up soil crusts, in conjunction with curative chemical applications, can help break the crusty barrier formed by cyanobacteria, creating drier surface conditions that are less conducive to cyanobacteria growth. Breaking up this barrier is essential for promoting turfgrass recovery through vegetative means or seeding. Spiking, slicing, aggressive vertical mowing and even using spiked hand tools will disrupt the blue-green algae mat and facilitate recovery. It is important to assess turfgrass health in the area before executing mechanical practices. If the turf is already weak and environmental conditions are not conducive for recovery and reestablishment, it is best to postpone these practices until conditions improve.

Since blue-green algae are photosynthetic organisms, limiting their ability to photosynthesize by applying topdressing will aid in control. Just like mechanical control measures, it is important to consider the effect topdressing sand will have on surrounding weakened turf before making an application for cyanobacteria control. When in doubt, be conservative and minimize potential risks to existing turf cover.

Manage moisture after blue-green algae infestation

Nursing turf back to health following blue-green algae infestation and control is often difficult because weakened turf areas or new seedlings need additional moisture, but surplus moisture can promote cyanobacteria recovery as well. Finding the right balance requires targeted moisture management, ideally with a portable moisture meter and hand watering, to provide enough water for recovery without applying too much.

Final Thoughts

Cyanobacteria, more commonly known as blue-green algae, are incredible organisms. They were among the first oxygen-producing organisms on Earth and helped shape the environment we inhabit today (Aiyer, 2022; Belnap & Gardner, 1993), but they can be very disruptive in a putting green setting. There are effective treatment options, but it is easy to end up in a cycle of treatment, the issue returning, and then treating again. To truly solve the problem, you need to look at the broader management context and take steps to promote healthier turf and create a less hospitable environment for blue-green algae to thrive. If you have any questions about how to manage or prevent cyanobacteria development on your golf course, reach out to your local USGA agronomist.

References

Aiyer, K. (2022). The Great Oxidation Event: How Cyanobacteria Changed Life. ASM.org.

Belnap, J., & Gardner, J.S. (1993). Soil microstructure in soils of the Colorado plateau: The role of the cyanobacterium Microcoleus vaginatus. The Great Basin Naturalist, 53(1), 40-47.

Clarke, B.B., Vincelli, P., Koch, P., & Chou, M.Y. (2024). Chemical control of turfgrass diseases 2024. (Extension Publication PPA-1) [1]. University of Kentucky Cooperative Extension Service.

Debnath, M., Mandal, N.C., & Ray, S. (2012). Effect of fungicides and insecticides on growth and enzyme activity of four cyanobacteria. Indian Journal of Microbiology, 52(2), 275-280.

Inguagiato, J.C., Kaminski, J.E., & Lulis, T.T. (2017). Effect of phosphite rate and source on cyanobacteria colonization of putting green turf. Crop Science, 57(S1), S-274.

Polyak, Y.M., & Sukharevich, V.I. (2025). Allelopathic properties of cyanobacteria (Review). Inland Water Biology, 18, 565-574.

Tao, H., Fang, C., Xiao, Y., & Jin, Y. (2024). The toxicity and health risk of chlorothalonil to non-target animals and humans: A systematic review. Chemosphere, 358, 142241.

Tredway, L.P., Stowell, L.J., & Gelernter, W.D. (2006). Yellow spot and the potential role of cyanobacteria as turfgrass pathogens. Golf Course Management. PACE Turfgrass Research Institute, San Diego, 83-86.

Stier, J. (2006). Shorter mowing heights are hazardous to summer health. The Grass Roots.