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From the November 2016 issue of GCM magazine:

GCSAA research update

Reports on GCSAA-funded research related to golf course management.

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Editor’s note: The GCSAA Research Grant Program is dedicated to funding applied agronomic, environmental and regulatory research that will benefit golf course superintendents and the courses they manage. Each year, scientists are invited to submit proposals, which are reviewed by a committee made up of turfgrass scientists and golf course superintendents that selects projects for funding through the Environmental Institute for Golf (EIFG), GCSAA’s philanthropic organization. The research projects described here were selected in late 2015, with the investigators receiving funding in 2016. Because most turf research is funded for two years, the work described here is in various stages of completion.

Using bentgrass tolerance, disease predictive models and fungicide timing to control dollar spot on fairway turf

James A. Murphy, Ph.D., James Hempfling and Bruce B. Clarke, Ph.D.

Bentgrass cultivars vary in their tolerance of dollar spot (clockwise from top left): 007, Declaration, Shark, Independence, Penncross and Capri.
Photo by James Hempfling

The overall goal of our research is to develop best management practices for the control of dollar spot disease caused by the fungus Sclerotinia homoeocarpa F.T. Bennett, a common and persistent disease of golf course turf throughout much of the world. This research project is organized into two trials managed as fairway turf. The objectives of the first trial include: evaluating dollar spot incidence and disease progress on six bentgrasses that vary in tolerance to dollar spot disease, and assessing the reliability of two existing weather-based models for predicting dollar spot epidemics on those cultivars and species. The second trial objectives include: evaluating the effect of pre-symptomatic (initial) timings for fungicide application on dollar spot incidence and disease progress on a susceptible and a tolerant bentgrass cultivar, and determining the extent to which pre-symptomatic fungicide application(s) on a susceptible and a tolerant bentgrass cultivar may affect the total fungicide usage over a growing season when subsequent fungicide applications are based on either a disease-threshold or predictive model.

Our first trial is evaluating six bentgrass cultivars [Independence, Penncross, Shark, 007 and Declaration creeping bentgrass (Agrostis stolonifera), and Capri colonial bentgrass (A. capillaris)] that vary in tolerance to dollar spot. They were seeded in North Brunswick, N.J., during September 2014. Disease severity was assessed every two to five days and compared with a growing degree day (GDD) model for predicting the onset of disease symptoms, and with a logistic regression model for predicting season-long disease activity. An accurate prediction of the onset of disease symptoms in highly susceptible cultivars occurred with the GDD model during 2015 but not 2016. A high risk of dollar spot was forecast by the logistic regression model one week before symptoms first appeared in highly susceptible cultivars during both years. Throughout the rest of the growing season, disease forecasting by the logistic regression model was fairly accurate for highly susceptible cultivars during 2015, but over-predicted during 2016. Disease forecasting on tolerant cultivars has not been accurate with either model in both years of this study.

Our second trial is studying the factors of bentgrass tolerance to dollar spot, initial fungicide application timing, and subsequent fungicide timing. Declaration (tolerant) and Independence (susceptible) were the cultivars used for the bentgrass tolerance factor. Initial fungicide application timings occurred (1) at the first appearance of disease symptoms (threshold-based; < 2 infection centers/8 square feet); (2) on May 20 (calendar-based); (3) when the logistic regression model reached a 20% risk index; or (4) at a GDD range of 20-30, 30-40, 40-50, 50-60, or 60-70 (base temperature 59 F [15 C] starting April 1). Subsequent fungicide timings were based on the logistic regression model or on a disease threshold, or were withheld completely to assess long-term effects of initial fungicide timings. All possible combinations of initial and subsequent fungicide timings were applied on both cultivars, and all fungicide applications used Emerald 70WG (boscalid, BASF) at 0.18 ounce/1,000 square feet (0.055 gram/square meter). Threshold-based plots were monitored as often as daily for dollar spot incidence. The number of applications in threshold- and model-based plots were recorded.

The initial fungicide application factor had minimal impact on long-term (May through November) control of dollar spot during 2015. Conversely, the factors of subsequent fungicide timing and bentgrass cultivar had a much greater impact on disease control. Excellent (<1 infection center/8 square feet [<1/0.74 square meter]) long-term control of dollar spot was achieved for both cultivars when subsequent fungicide timing was based on either the logistic regression model or the calendar-based program. The logistic regression model reduced fungicide inputs by one application compared with the calendar-based program (nine applications). Good to excellent long-term disease control was also achieved when subsequent fungicide timing was based on a threshold program, but the total fungicide input and the level of disease control depended on the cultivar and initial fungicide timing. Subsequent fungicide applications on Declaration plots that were threshold-based produced excellent disease control and resulted in only three fungicide applications, regardless of the initial fungicide application date. In contrast, the threshold schedule for subsequent applications on Independence plots resulted in a total of six or seven fungicide applications, depending on the initial fungicide timing. Moreover, disease incidence occasionally surpassed the target threshold value on Independence plots, and reached levels (up to 3.5 infection centers/8 square feet [3.5/0.74 square meter]) during the growing season that may not be acceptable at some golf courses. This research is being continued in 2017.

James A. Murphy is an extension specialist in turfgrass management, James Hempfling is a graduate research assistant, and Bruce B. Clarke is the director of the Rutgers Center for Turfgrass Science and an extension specialist in turfgrass pathology in the Department of Plant Biology and Pathology at Rutgers University, New Brunswick, N.J.

Chemical priming for creeping bentgrass stress tolerance

Francois Xavier Rucamumihigo and Emily B. Merewitz, Ph.D.

The study, which aims to show whether certain treatments can promote creeping bentgrass drought tolerance, is taking place at the Hancock Turfgrass Research Center at Michigan State University on a field equipped with a rainout shelter.
Photo by Francois Xavier Rucamumihigo

Priming of plants means that a given treatment makes plants more ready to take on a subsequent stress. Currently there are few controlled research studies available that show how priming chemicals for turfgrass species affects abiotic stress. Many new turfgrass products contain ingredients that may affect the systemic acquired resistance (SAR) or induced systemic resistance (ISR) pathways, which are the pathways associated with plant priming. Salicylic acid and jasmonic acid are the two plant hormones that signal SAR and ISR responses. Another important plant metabolite that can be used for priming is gamma amino butyric acid (GABA). Plant growth regulators that inhibit gibberellic acid biosynthesis are widely used in turfgrass management and can have a significant effect on the content of other hormones in the plant, such as jasmonic acid, salicylic acid and GABA. A plant growth regulator, Primo (trinexapac-ethyl, Syngenta), promoted a greater level of salicylic acid accumulation and decreased jasmonic acid in plants under drought stress (1). Thus, is an application of Primo combined with salicylic acid an unnecessary practice? Would an exogenous application of jasmonic acid in combination with Primo be beneficial? Plant-health-promoting products that contain salicylic acid are specialty products and can be quite costly for turf managers.

This study therefore aims to determine whether jasmonic acid, salicylic acid or GABA alone or in combination with Primo are effective treatments to promote creeping bentgrass drought tolerance. The study is taking place at the Hancock Turfgrass Research Center at Michigan State University on a field equipped with a rainout shelter (32 feet × 72 feet [10 meters × 22 meters]). The field was seeded in fall 2015 and is being maintained as a putting green. The field has a hand-irrigated block and a drought-control block all under the field shelter.

The following treatments are replicated inside each block: 1) control; 2) Primo Maxx (0.125 fluid ounce/1,000 square feet [0.039 ml/square meter]); 3) salicylic acid (0.5 mM); 4) GABA (50 mM); 5); jasmonic acid (0.5 mM); 6) Primo + salicylic acid; 7) Primo + GABA; and 8) Primo + jasmonic acid. The chemical and drought treatments were applied in midsummer 2016. Visual turf quality ratings, canopy reflectance (normalized difference vegetation index, NDVI), chlorophyll content (Field Scout CM1000 meter), soil volumetric water content and canopy temperature depression (infrared gun) were recorded. Leaf tissues were collected for evaluation of the level of relative water content, lipid peroxidation, antioxidant enzyme activities and hydrogen peroxide content, and this will continue every seven days. Water use was evaluated by measurements of evapotranspiration through mini-lysimeters installed in each plot (4-inch [10-cm] diameter PVC pipe). Data analysis is currently being conducted to determine treatment effects. A similar experiment is currently being conducted in the growth chamber. The experiment will be repeated in summer 2017.

Literature cited

1. Krishnan, S.K., and E. Merewitz. 2015. Drought stress and trinexapac-ethyl modify phytohormone content within Kentucky bluegrass leaves. Journal of Plant Growth Regulation 34:1-12 doi: 10.1007/s00344-014-9434-0

Francois Xavier Rucamumihigo is a graduate student and Emily B. Merewitz () is an assistant professor in the Department of Plant Soil and Microbial Sciences at Michigan State University, East Lansing, Mich.

Optimal management programs for annual bluegrass weevil populations with different insecticide resistance levels

Albrecht M. Koppenhöfer, Ph.D.; Olga Kostromytska, Ph.D.; and Shaohui Wu, Ph.D.

Figure 1. Densities of annual bluegrass weevil developmental stages in early June (peak fourth to fifth instar) in two golf course fairways (A, B) treated with BotaniGard (BG), Talstar (Tal), and a combination of the two (BG+Tal). In both fairways A and B, Talstar at the full rate was applied once just before peak densities of overwintered adults, and BotaniGard was applied just before peak adult densities and again one week later. In fairway B, there were two addi-tional treatments: Talstar was tested at half-rate applications one week apart (Tal2) and in combination with BotaniGard (BG+Tal2). Means with the same letter did not differ significant-ly (P > 0.05). An asterisk indicates a synergistic interaction.

The annual bluegrass weevil (ABW) is a serious and expanding pest with a demonstrated ability to develop resistance to a range of insecticides under the commonly used management regimes (that is, multiple applications of synthetic insecticides per season). Through previous research, we have developed a better understanding of the degree and scope of insecticide efficacy in laboratory and greenhouse experiments. In the ongoing study, we continue these studies in a two-pronged attack on the resistance issues.

Insecticide resistance studies in the field

We tested the efficacy of standard insecticides against ABW adults, young larvae and midsize larvae on golf course fairways at courses with about 2×, 30×, 100× and 340× pyrethroid resistance compared with our most susceptible population at Rutgers Hort Farm No. 2. Dursban (chlorpyrifos, Dow AgroSciences) applied at 1 pound a.i./acre (1.12 kilograms/hectare) was no replacement for pyrethroids for adult control. Control with Dursban averaged 50%, 39%, 24% and 15% at the 2×, 30×, 100× and 340× sites, respectively. Talstar (bifenthrin, FMC Corp.) applied at 0.1 pound a.i./acre (112 grams/hectare) averaged 70%, 67%, 43% and 10% control at the 2×, 30×, 100× and 340× sites, respectively. Ference (cyantraniliprole, Syngenta) applied at 0.16 pound a.i./acre (179 grams/hectare) was not affected by pyrethroid-resistance level or timing (versus early larvae, which coincide with late-bloom dogwood; or versus midsize larvae, coinciding with full-bloom rhododendron), and provided 68% to 99% control (88% overall average). Conserve (spinosad, Dow AgroSciences) applied at 0.4 pound a.i./acre (448 kilograms/hectare) versus midsize larvae averaged 80% control at the 2× and 30× sites, and 63% at the 100× and 340× sites.

All other larvicides were clearly affected by pyrethroid resistance level. Acelepryn (chlorantraniliprole, Syngenta) applied at 0.16 pound a.i./acre (179 grams/hectare) showed no clear effect of timing and averaged 66%, 58%, 31% and 12% at the 2×, 30×, 100× and 340× sites, respectively. Arena (clothianidin, Valent available through Nufarm USA) applied at 0.25 pound a.i./acre (280 grams/acre) was on average about 10% better versus young larvae, and averaged 51%, 53%, 10% and 12% control at the 2×, 30×, 100×, and 340× sites, respectively. Provaunt (indoxacarb, Syngenta) applied at 0.225 pound a.i./acre (252 grams/hectare) against midsize larvae averaged 75%, 80%, 75% and 15% control at the 2×, 30×, 100× and 340× sites, respectively. And Dylox (trichlorfon, Bayer) applied at 6.0 pounds a.i./acre (6.7 kilograms/hectare) versus midsize larvae averaged 66%, 73%, 30% and 25% at the 2×, 30×, 100× and 340× sites, respectively.

Exploring biorational insecticides for ABW management

Molt-X is based on the botanical azadirachtin and acts primarily as an insect growth regulator that disrupts the molting process. Two applications (each at 0.5 fluid ounce/1,000 square feet [0.16 ml/square meter]) applied about one week apart, targeting peak eggs and peak first larval stage or peak first larval stage and peak second larval stage, quite consistently gave around 40% control of the spring generation against pyrethroid-susceptible and pyrethroid-resistant (60×) ABW populations. Applied against later stages, Molt-X was less effective.

BotaniGard ES is a liquid emulsifiable formulation of the entomopathogenic fungus Beauveria bassiana GHA strain. By itself, this product provided 0%-40% control of ABW adults in spring. Talstar alone also attained only 0%-40% control of a pyrethroid-resistant ABW population. However, combinations of BotaniGard ES (total of 4 fluid ounces/1,000 square feet [1.27 ml/square meter]) with Talstar at 0.1 pound a.i./acre applied around peak adult densities in spring consistently synergized and provided 70% to 84% control of the spring generation of the pyrethroid-resistant ABW population. This result was achieved whether BotaniGard ES was applied all at once or was split into two applications about one week apart (Figure 1). The synergism in this combination appears to be based on the BotaniGard ES formulation’s improvement of the activity of the pyrethroid (likely by accelerating/enhancing penetration into the insect). The caveat with this combination is that it seems to be based in good part on the activity of the pyrethroid and would therefore exacerbate the development of pyrethroid resistance if it were overused.

Albrecht M. Koppenhöfer is a professor and extension specialist in turfgrass entomology, Olga Kostromytska is a research project assistant, and Shaohui Wu is a post-doctoral associate in the Department of Entomology at Rutgers University, New Brunswick, N.J.

Selection and use of wetting agents to improve infiltration and re-wettability on water-repellent sand greens

Xi Xiong, Ph.D.; Stephen Anderson, Ph.D.; and Keith Goyne, Ph.D.

Severe localized dry spot (LDS) developed on a creeping bentgrass green built according to USGA recommendations at the turfgrass research facility at the University of Missouri. Note the damaged turf areas inside the plots (front part of the green) where no wetting agent applications were made.
Photo by Xi Xiong

Soil water repellency is a widespread problem affecting pastures, agronomic fields, forests and other natural areas, especially where sandy soil is abundant. It is not fully understood, but evidence suggests that soil water repellency is due to the coating of organic compounds on the surface of sand particles, which has been attributed to the activity of soil microbes and, in some cases, plant species. Within the turf community, water-repellent soil is known to cause localized dry spot (LDS) on sand-based greens on golf courses. Without treatment, water bypasses hydrophobic root zones and causes preferential flow, ultimately leading to plant death in the affected area (see photo).

Application of wetting agents is the primary strategy used to improve water infiltration into water-repellent soil. The wetting agent molecules are amphiphilic compounds containing a hydrophobic group that can adhere to hydrophobic sand surfaces, and a hydrophilic group that can “hold on” to water molecules. By attaching to the hydrophobic sand surfaces, wetting agents can alter soil hydrophobicity and subsequently improve water infiltration into water-repellent soil.

Despite the wide use of wetting agents by superintendents, the No. 1 question that remains unanswered is which wetting agent is the best. A number of factors currently prevent us from answering this question. One of these is variation in field conditions, such as the level and the consistency of soil hydrophobicity.

At the University of Missouri, a turf specialist, a soil physicist and a soil chemist have formed a collaborative team with the objective of improving our understanding of soil hydrophobicity and wetting agents. In the past three years, our team has made two major breakthroughs related to the effect of wetting agents on soil infiltration.

The first breakthrough was to artificially treat sand that meets USGA recommendations for greens construction in order to make it water-repellent. The treated sand demonstrated steady and consistent water repellency, and the level of hydrophobicity was determined to be severe, because the water droplets never penetrated into the sand layers and eventually evaporated. Artificially developed hydrophobic sand avoids the difficulties associated with inconsistent levels of hydrophobicity across space and time in naturally occurring hydrophobic sand, which experiences changes in hydrophobicity as soon as it comes in contact with water.

The second breakthrough was the determination of a relationship between measurable properties of a given wetting agent, such as surface tension, and its effect on infiltration into hydrophobic sand. This was conducted by using a piece of sophisticated equipment called a tensiometer, which allows us to precisely evaluate a wetting agent solution’s surface tension as a function of its concentration. For example, our research found that the wetting agent Cascade Plus at concentrations ≥3,000 mg/liter (less than half the suggested label rate) maintained a surface tension that is lower than the 90-degree surface tension at 31.3 milliNewton/meter determined for the artificially made hydrophobic sand. This result means that Cascade Plus at this concentration or higher can spontaneously wet the water-repellent sand.

In comparison, wetting agent Surfside 37 showed a higher surface tension even at 5,000 mg/liter. This means that Surfside 37 at this concentration will not infiltrate the hydrophobic sand unless a certain depth of solution (ponding head) exists above the sand surface in order to force the liquid into the sand layers. In another words, Surfside 37 at this concentration will not wet the hydrophobic sand. These results were corroborated by an infiltration study in which the infiltration rate of Cascade Plus was more than twice that of Surfside 37 at the tested concentrations.

This is an ongoing project. Our objective for this experiment is to test approximately 50 commonly used wetting agents for their surface tension at various concentrations, and relate their physical properties to infiltration. The ultimate goal is to develop a research-based guide for wetting agents by grouping them into categories in terms of their efficacy in facilitating water infiltration into hydrophobic soil.

Xi Xiong is an associate professor in the Division of Plant Sciences, Steven Anderson is a William A. Albrecht Distinguished Professor in the Department of Soil, Environmental and Atmospheric Sciences, and Keith Goyne is an associate professor in the Department of Soil, Environmental and Atmospheric Sciences and associate director of the School of Natural Resources at the University of Missouri, Columbia, Mo.

Performance and recovery of four turfgrass species subjected to golf cart traffic during prolonged drought

Ross Braun; Dale Bremer, Ph.D.; and Jared Hoyle, Ph.D.

Field plots at Rocky Ford Turfgrass Research Center, Manhattan, Kan., on June 24, 2016 (before the drought period and without traffic). Photos by Ross Braun

Field plots at Rocky Ford Turfgrass Research Center, Manhattan, Kan., on Aug. 6, 2016, after 41 days of simulated drought, with no irrigation and a total of 96 golf cart traffic passes applied inside the white lines.

Field plots at Rocky Ford Turfgrass Research Center, Manhattan, Kan., on Sept. 15, 2016, after 40 days of recovery with no simulated golf traffic applied since Aug. 6, 2016.

One of the biggest challenges facing golf course superintendents is decreasing water available for irrigation. Increasingly, state and local drought restrictions may be imposed on turf managers, with no regard for damage to turfgrass (1). During periods of severe drought and water shortages, turfgrass may receive little to no irrigation for extended spans of time (2).

Traffic damage is another management issue superintendents commonly face. Traffic, such as that near cart paths where golfers tend to either walk or drive carts into fairways and roughs, may cause significant wear to turfgrass and also compact the soil. These factors result in, among other things, reduced tolerance to heat and drought stresses (3). In fact, when the soil is compacted, more-frequent irrigation is often required to compensate for the detrimental effects of compaction on root and shoot growth.

Significant research has been conducted separately into the issues of drought resistance and traffic tolerance in turfgrass. Results have indicated that turfgrasses vary widely in their ability to resist drought and tolerate traffic. However, little research has been conducted to investigate the combined effects of drought and traffic in turfgrasses. Given the increasing likelihood of irrigation restrictions for turfgrass at operational golf courses with areas of high traffic, conducting such research is imperative.

Therefore, the objective was to evaluate the combined effects of golf cart traffic on both warm-season (C₄) and cool-season (C₃) turfgrass species maintained at fairway or rough mowing heights during a simulated drought period and a subsequent recovery period (without traffic).

A field study was conducted at the Rocky Ford Turfgrass Research Center at Kansas State University in Manhattan, Kan., in 2015 and 2016 under a stationary rainout shelter measuring 96 feet long × 34 feet wide (29.26 meters × 10.36 meters). The soil was a silt loam.

The study included three main effects: four turfgrass species, two mowing heights and two traffic rates, with each treatment replicated four times. Two warm-season species — Sharps Improved II buffalograss [Buchloe dactyloides (Nutt.) Engelm.] and Meyer zoysiagrass (Zoysia japonica Steud.) — and two cool-season species — America Kentucky bluegrass (Poa pratensis L.) and Paragon GLR perennial ryegrass (Lolium perenne L.) — were maintained at golf course fairway height (0.625 inch [1.6 cm]) and rough height (2.5 inches [6.35 cm]) under a strip-split plot arrangement. Traffic rates consisted of no traffic (untreated) and traffic (16 passes a week) with an electric EZ-GO TXT utility (golf) cart with supplemental weight to simulate two golfers and equipment during the drought period.

Prior to and throughout the research trials, both warm- and cool-season turfgrasses were maintained individually according to standard agronomic practices (fertility and pest control). In both years, a clear plastic greenhouse cover was installed during late June to exclude rainfall, and turfgrasses underwent a 41-day simulated drought period with no irrigation and simulated traffic applied to plots weekly. At the end of the 41-day drought period, the plastic cover was removed and turfgrasses received adequate water requirements via irrigation and precipitation. Visual turf quality, soil moisture, turf firmness and percent green cover (measured via digital photography) were measured weekly over both drought (41 days) and recovery (40 days) periods. Soil bulk density and soil compaction measurements were measured during pre- and post-drought periods. Root measurements were conducted immediately following the post-drought period in 2016 to evaluate the effects of drought and traffic on root-length density, root surface area, average root diameter and root biomass.

Preliminary results from 2015 indicated differences in visual quality, percent green cover and soil bulk density, especially among turfgrass species and between traffic treatments, and to a lesser extent, between mowing heights. Visually, the warm-season species performed better during the drought and were faster to return to acceptable quality during recovery. With one exception, all four turfgrass species returned to acceptable quality by the end of the 40-day recovery period in both years. The exception was Kentucky bluegrass mowed at rough height, which did not recover in 2016. Analysis of data from this project is ongoing.

Results from this research will be distributed in GCM and other trade publications, via digital outlets (Twitter, Facebook, newsletters and blogs), and in local and regional educational programs (field days, seminars, conferences and GCSAA chapter meetings). This research will be useful for superintendents — particularly those working in the stressful environment of the transition zone — who manage any of the turf species investigated in the project.

Literature cited

1. Beard, J.B., and M.P. Kenna, editors. 2008. Water quality and quantity issues for turfgrasses in urban landscapes. Council for Agriculture Science and Technology, Ames, Iowa.
2. Steinke, K., D. Chalmers, J. Thomas, R. White and G. Fipps. 2010. Drought response and recovery characteristics of St. Augustinegrass cultivars. Crop Science 50(5):2076-2083. doi:10.2135/crop sci2009.10.0635
3. Turgeon, A.J. 2012. Turfgrass management, 9th ed. Pearson Education, Upper Saddle River, N.J.

Ross Braun is a Ph.D. student in turfgrass science, Dale Bremer is a professor and director of graduate programs, and Jared Hoyle is an assistant professor and extension turfgrass specialist in the Department of Horticulture and Natural Resources at Kansas State University, Manhattan, Kan.

An enzymatic approach to remediate water repellency of turfgrass soils

Paul Raymer, Ph.D.; Jack Huang, Ph.D.; and David Jespersen, Ph.D.

Water sitting on hydrophobic sand used in our pot studies. Hydrophobic sand was provided courtesy of Gerald Henry, Ph.D.,
of the University of Georgia.
Photo by Paul Raymer

Soil water repellency occurs on sandy turfgrass soils as localized dry spots (LDS) and within the dry area of fairy ring disease areas. Soil water repellency causes serious soil water infiltration/runoff problems and reduces turf quality. Our research explores a new and novel approach to alleviate soil water repellency by using direct application of enzymes that are specific for degradation of hydrophobic organic fractions thought to contribute to soil water repellency. Because these enzymes directly degrade or alter the organic coatings, they should provide for longer-term and more effective alleviation of soil water repellency than the current management approach, which is the repeated use of wetting agents.

In proof-of-concept laboratory studies funded by the University of Georgia Technology Commercialization Office, we identified a number of enzymes and multiple extracts from biomass fermentation that have the potential to alleviate soil water repellency. We submitted a patent application (1) based on this laboratory data and have published two journal articles (2,3). The first article represents the first report of the use of enzymes for alleviation of soil water repellency. With USGA-sponsored research funds, we compared the effectiveness of wetting agents and two enzymes and their combinations in relieving soil water repellency associated with both LDS and fairy ring in small field plots on the University of Georgia Griffin campus. In April 2015, we established research at The Old Collier Golf Club in Naples, Fla., comparing an enzyme and a wetting agent (Revolution) and their combination for long-term effectiveness in treating LDS. These previous studies clearly establish the potential of this technology to provide more effective and lasting alleviation of soil water repellency issues on golf courses.

This current research builds on these previous efforts and proposes both greenhouse and field studies using direct application of enzymes or combinations of enzymes and wetting agents as a means to degrade certain organic fractions thought to contribute to soil water repellency. The enzymes proposed are found in natural systems, and enzyme activity is much less affected by changes in field environmental conditions than are specific microbial populations. We would anticipate that enzyme treatments could be confined to the localized soil water repellency areas (spot treatment) as a corrective and possibly preventive measure.

The objectives of the proposed project are to refine application protocols through greenhouse experiments that determine the most cost-effective enzyme application rate and application frequency for the treatment of soil water repellency/LDS. Additionally, the effectiveness of adding wetting agents in combination with enzymes to enhance enzyme penetration is being evaluated. Field evaluations involving the most effective and economic treatments based on our greenhouse research will be evaluated for both short-term (< 2 weeks) and long-term (season-long) effectiveness in small-scale plot trials on the University of Georgia Griffin campus, and with more limited treatments at The Old Collier Golf Club in Naples, Fla.

Enzyme-facilitated alleviation of soil water repellency conditions on turfgrass sites holds great potential to provide an effective new approach for managing LDS conditions for longer periods of time than do wetting agents. These studies will bridge gaps to bring this new approach from the proof-of-concept phase (laboratory) to practical field application.

Correction of soil water repellency/hydrophobic areas expressed as normal LDS on sand soils or as fairy rings on more diverse soil types is essential for efficient irrigation application and for vigor and quality of golf course turfgrass areas — greens, tees, fairways and roughs. The application of enzymes to provide longer-term remediation of soil water repellency/LDS would be a valuable management option for water conservation best management practices and sustainable management of golf courses.

Literature cited

1. Huang, Q., R.N. Carrow and P.L. Raymer. 2015. Methods and composition to reduce soil water repellency. U.S. Utility Patent US2015/0166889 A1.
2. Liu, J., L. Zeng, R.N. Carrow, P.L. Raymer and Q. Huang. 2013. A novel approach for alleviation of soil water repellency using a crude enzyme extract from fungal pretreatment of switchgrass. Soil Research 51(4):322-329.
3. Zeng, L., J. Liu, R.N. Carrow, P.L. Raymer and Q. Huang. 2014. Evaluation of direct application of enzymes to remediate soil water repellency. HortScience 49:662-666.

Paul Raymer is a professor, Jack (Qingguo) Huang is an associate professor, and David Jespersen is an assistant professor in the Department of Crop & Soil Sciences on the Griffin campus of the University of Georgia, Griffin, Ga.

Late-fall wetting agent application to enhance winter survival of ultradwarf greens

Douglas E. Karcher, Ph.D.; Michael Richardson, Ph.D.; and Eric DeBoer

Plots treated with various wetting agents exhibit enhanced spring green-up relative to untreat-ed check plots (highlighted) on a TifEagle ultradwarf bermudagrass putting green in Fayette-ville, Ark.
This photo was taken April 19, 2016.
Photo by Michael Richardson

The use of ultradwarf bermudagrasses on putting greens has increased throughout the transition zone in the past decade. A significant management challenge with these greens is winter survival and spring recovery. Late-season wetting agent applications might improve soil moisture retention and uniformity in ultradwarf bermudagrass putting greens. This could be further enhanced with higher application rates given that phytotoxicity is less likely during cool weather. If effective, this strategy would ultimately improve the winter survival and spring green-up of ultradwarf bermudagrass putting greens. Therefore, the objective of this study is to determine whether late-fall wetting agent applications improve the winter soil moisture retention — and, consequently, the winter survival — of ultradwarf bermudagrass putting greens in the transition zone.

This research was initiated in December 2015 in northwest Arkansas at two experimental sites. The first location was a TifEagle research putting green at the University of Arkansas experiment station (Fayetteville, Ark.), and the other location was a Champion practice green at The Blessings Golf Club (Johnson, Ark.). Wetting agent treatments were initiated at both locations before winter covers were applied. These trials are located within a region where winter injury on ultradwarf greens is routinely observed.

Wetting agent treatments include products that have a history of good efficacy and are commonly used throughout the region. These treatments include products that are typically applied monthly as well as those that are marketed for long-term effects on soil wettability. In addition, all wetting agent products tested were applied only once at a 1× and 2× label rate. All wetting agents were watered in with at least 0.2 inch (5 mm) shortly after application.

Ultradwarf putting green plots were evaluated each month following treatment application for soil moisture uniformity, and for soil wettability at one and four months following treatment applications. Plots were evaluated for visual turf quality and green coverage during spring green-up. The first season of data collection has been completed, but statistical analysis of these data is still in progress. Although there are no definitive conclusions at this time, it is evident that when some wetting agent products are applied in late fall, they may have a positive impact on winter survival and spring green-up (see photo). These trials will be repeated this December, and final conclusions from this two-year study will be available at the end of next year.

Douglas E. Karcher and Michael Richardson are professors and Eric DeBoer is a graduate student in the Department of Horticulture at the University of Arkansas in Fayetteville, Ark.