Super Science: A recap of the research published in 2025

Another year has passed quickly. Here is a summary of the excellent research information provided by turfgrass researchers and the USGA Green Section that appeared in Golfdom this year.

January: Can golf course ponds be a safe haven for amphibians?

By Michelle Boone and Holly Puglis

Although a golf course will never replace unfettered nature, it can serve as a green space that helps preserve some of the local biodiversity. Golf courses can potentially benefit amphibians, such as frogs and salamanders, which are experiencing declines worldwide due to habitat loss, disease, chemical usage and the introduction of exotic species. 

Looking to nature as a guide for management can serve as a means of preserving all the necessary habitat components and restoring ecosystem services in managed areas. With over half of the world’s wetlands lost, habitat destruction is a significant issue for aquatic species that rely on these ecosystems for survival. When green spaces, such as golf courses, can help mitigate the effects of habitat destruction to some extent, everyone benefits.

Research Takeaways

• Amphibian communities are most diverse in habitats with temporary ponds since these habitats are nutrient-rich and lack fish, predators that frequently eliminate most species of amphibians.
• Cricket frog (Acris crepitans) and green frog (Rana clamitans) survival was reduced dramatically when reared in experimental ponds with grass carp (Ctenopharyngodon idella) or predatory bluegill sunfish (Lepomis macrochirus).
• For grassland species like cricket frogs, unmown fields provide a refuge from the desiccation of the sun and wind, a place to hide from predators, a pathway to disperse and a source for insects on which they prolifically feed.
• Buffer zones of three feet or more around ponds increased the survival of cricket frogs.

Adapted from Michelle D. Boone, Ph.D., and Holly J. Puglis. 2013. Keeping all the Pieces: Restoring Natural Processes for Easier Golf Course Management. USGA Turfgrass and Environmental Research Online. 12(4):1-5.

February: Understanding nematode depth and distribution in bentgrass greens

By Asa McCurdy, Jefferson Barizon, and G.L. Miller

Plant-parasitic nematodes (PPNs) present a serious threat to the health and aesthetic quality of golf course putting greens. The sand-based root zones commonly used in these greens offer large pore spaces that facilitate nematode movement and population growth. Combined with the high levels of stress caused by frequent mowing and aggressive maintenance, even minimal feeding damage by PPNs can have significant effects. However, effective control of these pests is challenging.

One major obstacle to controlling PPNs is the limited mobility of many nematicides. These chemicals often have low water solubility and a high affinity for organic matter, causing them to remain in the thatch layer rather than reaching nematodes deeper in the soil. Additionally, PPN species differ in their behavior and location within the root zone; some reside inside plant roots, while others remain in the soil. This study investigated whether PPN populations, specifically lance (Hoplolaimus spp.) and root-knot (Meloidogyne spp.) nematodes, reach a peak at a consistent and targetable soil depth and time of year on putting greens in Missouri and Indiana to improve nematicide timing and effectiveness.

Research Takeaways

• Overall, PPN populations were more abundant in Indiana (2022) than in Missouri/Kansas (2021), possibly due to the lack of nematicide applications at Indiana sampling sites. Lance nematodes were targeted and more prevalent at Missouri/Kansas sites, while root-knot and ring nematodes were more abundant in Indiana sites.
• In October, lance nematode populations in Missouri/Kansas (2021) peaked in the 0–5 cm soil depth, showing significant depth-by-month interactions. 
• Root-knot nematode populations in Missouri/Kansas (2021) were consistent across months, with the highest density at 0–5 cm depth. Indiana (2022) populations peaked in April, with higher densities in the upper soil layers (0–10 cm).
• Ring nematodes were the most abundant parasitic nematodes found in both regions, with higher populations in Indiana sites. Ring nematodes, however, do not cause as much feeding damage as other species and are seldom above any action threshold. 

Adapted from McCurdy, Asa L., Barizon, Jefferson, and Miller, G.L. 2024. Depth distribution of plant-parasitic nematodes on bentgrass golf greens in Missouri and Indiana. Journal of Nematology. 56:1-15. DOI: 10.2478/jofnem-2024-0006

March: How much nitrogen is needed to establish seeded bermudagrass?

By Jada S. Powlen and Cale A. Bigelow

Common bermudagrass has become increasingly popular on golf courses in temperate regions due to genetic improvements that have enhanced the quality of seeded cultivars, making them comparable to vegetative hybrids. These improvements offer advantages such as easier establishment, greater genetic diversity, improved winter hardiness and lower costs. However, while nitrogen (N) guidelines for mature turf are well-established, optimal N rates during seed establishment remain unclear. Some turf managers use extra nitrogen to accelerate establishment.  Still, excessive use — particularly of soluble N — can harm turf health, promote shallow roots and excessive growth, reduce rhizome development and increase the risk of nutrient runoff. 

Reducing application frequency and using controlled-release fertilizers may lower total nitrogen (N) requirements during establishment and reduce off-target N movement. A two-year field study was conducted to determine the optimal N establishment program for a seeded bermudagrass cultivar on native soil, using two N sources with varying application rates and frequencies.

Research Takeaways:

• ‘Rio’ bermudagrass was seeded in June 2020 and 2021, testing eight granular N-fertilizer programs using ammonium sulfate (AMS) or polymer-coated urea (PCU).
• Total N applied ranged from 0.0 to 6.0 lb. N per 1,000 ft², with application strategies including PCU only at planting and repeated applications of AMS every seven or 14 days after germination.
• Time to reach 50 percent green coverage (GC50) ranged from 20 to 24 days in the first year and 23 to 30 days in the second year, showing variation across N programs.
• Applying 2 lb. N per 1,000 ft² of PCU at planting achieved a similar time to 90 percent green coverage (GC90) compared with other fertilization programs, but with fewer applications and less total N used.
• Results suggest that applying more than 3 lb. N per 1,000 ft² during the first 60 days of establishment does not provide additional benefits regarding time to maximum turf coverage.

Adapted from Powlen, J. S., and Bigelow, C. A. 2024. Seeded bermudagrass establishment as affected by nitrogen source, rate, and application frequency. Crop, Forage & Turfgrass Management, 10,e20250. https://doi.org/10.1002/cft2.20250

April: Evaluating PGR reapplication on annual bluegrass putting greens 

By Chas Schmid and Alec Kowalewski

Plant growth regulators (PGRs) are commonly applied to golf course putting greens on a calendar-based schedule; however, growing degree-day (GDD) models have recently been developed to optimize reapplication intervals for season-long growth suppression, particularly for creeping bentgrass and hybrid bermudagrass, using products like Primo Maxx 1ME and Trimmit 2SC. However, no such models exist for annual bluegrass (ABG) putting greens, where superintendents currently rely on models based on bentgrass. While nitrogen (N) rate effects on ABG turf quality, disease susceptibility and playability are well documented, little is known about how N rate influences PGR performance or reapplication intervals. Higher N rates may necessitate more frequent PGR applications than predicted by current GDD models, underscoring the need for research to determine whether ABG-specific GDD models should be adjusted based on N rates.

For annual bluegrass putting greens, our objectives were to develop a growing degree day model for PGR (Primo Maxx and Anuew) application intervals and determine if nitrogen rate influences a growing degree day model.

Research Takeaways

• The predicted reapplication interval for Primo Maxx 1ME on annual bluegrass ranged from 309 to 217 GDD for low and high N rates, respectively.
• Primo, combined with high N, was like previous recommendations for bentgrass.
• The predicted reapplication interval for Anuew on annual bluegrass ranged from 243 to 212 GDD for low and high N rates, respectively; both estimates were lower than previous recommendations for bentgrass.
• Trends suggest reapplication intervals for PGR varied by month of application. 
• PGRs applied to annual bluegrass under stressful environmental conditions during July resulted in longer reapplication intervals, particularly when combined with low N rates, which increased intervals by greater than 130 GDD.

Adapted from Schmid, Chas, and Kowalewski, Alec. 2024. Influence of nitrogen rate on growing degree day models for plant growth regulator reapplication interval on annual bluegrass putting greens. 2024 USGA Davis Progress Reports. USGA ID# 2023-15-782, pp. 140-150.

May: An inside look at the USGA Water Conservation Playbook

By USGA Green Section

Golf courses are facing growing threats from rising water costs, unpredictable water supplies and increased water restrictions. Proactive water management is essential to secure the sport’s future.

The USGA has invested $30 million over 15 years to help courses reduce water use while maintaining playability and aesthetics. For over a century, the USGA has supported golf courses through research on turfgrass and resource management. Now, the organization is collaborating with turfgrass and golf course management leaders to drive water conservation across the industry.

Research Takeaways:

Experts have outlined in the USGA Water Conservation Playbook nine key actions in three major areas:

1. Fundamental Irrigation Stewardship

• Monitor water use, schedule irrigation based on weather and maintain systems to prevent leaks.
• Manage golfer expectations to balance playability and aesthetics with water conservation.
• Use water-efficient products to maintain turf quality under reduced irrigation.

2. Advanced Irrigation and Conservation Techniques

• Use soil-moisture sensors and remote sensing for precise, site-specific irrigation.
• Implement drought-tolerant turfgrass and reduce winter overseeding.
• Minimize irrigated acreage by replacing unnecessary turf with low-water plants and hardscape.
• Install subsurface drip irrigation to deliver water directly to roots and reduce waste.

3. Water Sourcing and Storage Stewardship

• Optimize surface water use by minimizing evaporation and seepage.
• Utilize alternative water sources, such as recycled wastewater, to reduce reliance on potable water.

June: Pythium species management recommendations

By Lee Butler and Jim Kerns 

Managing Pythium species is tough, particularly in the transitional climate zone, where temperature extremes complicate disease timing and reduce the efficacy of fungicides. The following are the current recommendations for managing Pythium blight, Pythium root rot and Pythium root dysfunction. The symptoms, development factors and cultural and chemical control are summarized.

Research Takeaways

• Symptoms and appearance: Pythium blight is a foliar disease, while Pythium root rot or dysfunction are root diseases but differ in appearance and host specificity.
• Development conditions: Pythium blight is driven by high humidity and leaf wetness, and Pythium root rot thrives in saturated soils at any time. Pythium root dysfunction infects bentgrass on putting greens in cool temperatures but can also appear under heat/drought stress.
• Cultural management: Pythium blight targets leaf wetness, poor airflow and excessive nitrogen. Focus on water management and drainage for root rot, while root dysfunction on putting greens emphasizes soil structure, root zone oxygen and drought mitigation.
• Chemical control: Pythium blight is mostly foliar-focused preventative applications, root rot is generally curative with a specific sequence of applications and root dysfunction requires precise fungicide classes and delivery to the root zone.

Adapted from Jim Kerns and Lee Butler, NC State University Extension, Turfgrass Diseases. Pythium Blight, Pythium Root Rot, and Pythium Root Dysfunction. Last updated 2025.

July/August: A million ways for grass to die in the winter

By Paul Koch

The past few winters in the Midwest have clearly demonstrated that what can kill your grass from one winter to the next can be completely different. In one winter, it might be early winter rainfalls and heavy late winter snowfall that led to destructive snow mold outbreaks. In another winter, it might be a nearly complete absence of snow that leads to widespread desiccation injury. However, regardless of the winter conditions, something can still harm or injure your grass. Let’s review the various types of winter injury that can occur and the best methods for preventing each one.

Research Takeaways

• Snow mold prevention and management: Snow mold, caused primarily by pink, gray or speckled fungi, is best prevented with one or two late-fall fungicide applications timed to avoid rainfall or snowmelt events, which can degrade protection. Cultural practices such as limiting late-fall nitrogen have modest effects, while potassium fertilization may increase or decrease snow mold depending on turf species.
• Recent snow mold pressure and research: Snow mold pressure was generally low across the northern U.S. last winter, with exceptions in certain pockets. Research trials in Wisconsin and Minnesota saw limited disease due to dry, cold conditions, while Marquette, Mich., had moderate pressure (54 percent in untreated plots). Fungicide treatments with multiple active ingredients provided excellent control, even under reduced pressure.
• Desiccation injury: Major issue across the western Great Lakes in 2023–24, caused by prolonged drought, cold snaps and wind exposure. Creeping bentgrass on elevated, sandy or thatchy sites was most affected. Research indicates that physical barriers, such as covers and heavy sand topdressing, offer the most effective protection, while wetting agents, pigments or anti-transpirants provide minimal benefit.
• Ice injury (crown hydration and ice encasement): Crown hydration occurs when water inside plant cells freezes, while ice encasement deprives turf of oxygen and accumulates toxic gases. These are more common in the Great Lakes and Northeast. Prevention strategies include surface drainage, avoiding sand dams and using covers to reduce water infiltration and limit ice contact.
• Direct low-temperature injury: Grass species vary in cold tolerance; annual bluegrass is injured near -4°F, while creeping bentgrass can survive near -40°F. Drought-stressed turf is more vulnerable, as seen with severe injury during the 2023–24 cold snap. Covers and heavy sand topdressing provide the only real protection.

September/October: New USGA research evaluating plant growth regulators

By Mike Kenna

The USGA continues to support research evaluating plant growth regulators and their impact on new creeping bentgrass cultivars, fertilizer rates and how they could aid in transitioning from annual bluegrass to bentgrass. Two research projects currently underway, one at the Ohio State University and the other at Rutgers University, are summarized in this article.

At Ohio State University, Ed Nangle, Ph.D., Dominic Petrella, Ph.D., and Florence Sessoms, Ph.D., are conducting a three-year project to evaluate how new creeping cultivars respond to lower nitrogen application rates, both in the presence and absence of various plant growth regulators. This research will help guide turfgrass management practices, especially for golf course superintendents transitioning greens to newer cultivars.

Research Takeaways

• Creeping bentgrass cultivars responded differently to lower rates of nitrogen.
• Two cultivars have already displayed significantly higher levels of organic matter accumulation than Penncross.
• Penncross displayed lower quality turf in response to lower nitrogen rates, while the new cultivars have provided higher levels of shear strength. 
• Penncross provided higher firmness numbers that align with less turfgrass in the canopy.
• Applications of Trimmit (paclobutrazol) and Anuew (prohexadione-calcium) led to enhanced shear strength.
• Applications of Trimmit and Anuew increased green speeds by 9 to 12 inches compared to the untreated control.

Adapted from Nangel, E.; Petrella, D.; and Sessoms, F. 2024. The impact of Nitrogen Rate and Growth Regulators on Modern Creeping Bentgrass Cultivars. USGA Mike Davis Program for Advancing Golf Course Management: 2024 Progress Reports. p326-331. USGA ID 2024-12-822.

At Rutgers University, Matt Elmore, Ph.D., and Jim Murphy, Ph.D., are finishing up with two projects to suppress annual bluegrass growth. Their first objective was to evaluate a combination of cultural (phosphorus and pH) and Trimmit (paclobutrazol) for annual bluegrass suppression in bentgrass putting greens (Project 1). They hypothesize that a strongly acidic rootzone (pH ~5.5) combined with relatively low rootzone phosphorus (6 to 10 ppm) will promote creeping bentgrass encroachment into annual bluegrass. 

They expanded the research to include an additional field trial to study the population dynamics of annual bluegrass and creeping bentgrass on putting greens using a five-level pH gradient and comparing ‘Penncross’ with ‘Oakley’ creeping bentgrass (Project 2). The 2024 objective was to adjust the phosphorus and pH levels in the annual bluegrass putting green before seeding creeping bentgrass and measuring its spread in 2025.

Research Takeaways

• The mat layer pH was adjusted from 6.0 to 6.3 to a mean of 5.3 in acidic plots and 6.3 in neutral pH plots (as of November 2024). The acidic treatments are exhibiting poorer turfgrass quality for annual bluegrass in summer.
• The phosphorus depletion target for Project 1 has not been achieved despite phosphorus not being applied in over two years. The mat layer P averaged 47 ppm (Mehlich III) across the site in November 2024, an increase from 38 ppm in May 2024.
• A mat layer pH gradient ranging from 4.8 to 7.0 was established for Project 2. Significant differences in annual bluegrass turfgrass quality are evident across the pH gradient.
• ‘Penncross’ and ‘Oakley’ bentgrasses were established in 2024 for transplant in 2025.

Adapted from Elmore, Matthew T., and Murphy, James A. 2024. Integrating phosphorus and pH management with a plant growth regulator for annual bluegrass suppression. USGA Mike Davis Program for Advancing Golf Course Management: 2024 Progress Reports. p332-336. USGA ID 2023-38-805. 

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