National Turfgrass Evaluation Program

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Organic Matter accumulation Trial

Reducing the Impact of Drought with Biostimulants – Can It Be Done?

M. Berger, T. Morris, E. Nangle

OSU CFAES Wooster Campus, Wooster OH 44691

Abstract

The golf course industry is known for its high water consumption, using nearly 2.08 billion gallons daily in the continental United States. Creeping bentgrass (Agrostis stolonifera L.), a popular cool-season grass on golf courses, has a high evapotranspiration rate, necessitating sustainable water management practices. Biostimulants, which are compounds or microorganisms that enhance plant nutrition and stress tolerance, could offer a solution by reducing water usage while maintaining turf quality. Although biostimulants have demonstrated success in other sectors, they remain understudied in turfgrass systems.

This study investigates the potential of a biological or biostimulant treatment to enhance creeping bentgrass’s response to water deficit stress. The research objectives are to: (1) assess whether biological treatments improve responses to water-deficit environments, (2) evaluate the efficacy of biological treatment-based biocontrol products or similar in reducing physiological stress in turfgrass, and (3) determine the persistence of applied biological treatments in different turfgrass soil types.

By understanding turfgrass responses to water stress and exploring the role of biological treatment biostimulants, this research aims to contribute to more sustainable water management practices in golf course maintenance.

Introduction

Turfgrasses are highly valued for their environmental benefits and their role in sports fields and golf courses—industries that have become both well-managed and lucrative. However, the significant water consumption in the golf course industry raises environmental concerns. Creeping bentgrass Agrostis stolonifera, widely used in cool-season courses, demands high maintenance, including substantial water usage, due to its high evapotranspiration rate. The species produces high quality playing surfaces and can tolerate extremely low mowing heights however and these desirable traits have not been found in other turfgrass species that might have lower water use requirements. Further to this the turfgrass species Annual bluegrass Poa annua has an even greater need for irrigation due to the notoriously short root structure combined with disease susceptibility and so turfgrass managers tend to try manage towards the creeping bentgrass species where possible.

To address these concerns, exploring innovative solutions like biostimulants is essential. Biological treatments, defined as beneficial compounds or microorganisms, could help reduce water usage while maintaining turf quality. Although they have shown promise in other applications, they remain understudied in turfgrass systems.

Rationale

Biostimulants present a potential alternative for improving plant health and mitigating environmental stressors. However, their application in the turfgrass industry is complex and not yet fully understood. Determining the critical water potential of creeping bentgrass seedlings and improving methods for screening germplasm for water deficit stress are crucial steps in managing the water requirements of golf courses. Further to this field trials should also be used for comparison purposes against what might be considered industry standards or similar products that might be of use.

Research Methods

This study evaluates the effectiveness of biological treatment products in mitigating water deficit stress on ‘Pure Distinction’ creeping bentgrass at research sites in Wooster, Ohio and a mixed stand of creeping bentgrass Agrostis stolonifera / annual bluegrass Poa annua. The trials were initiated at the Ohio State University Turfgrass Research Facility in Columbus, OH, and at the Ohio State ATI in Wooster, OH. The study uses a randomized complete block design with varying rates of the biological treatment and a urea treatment applied over two summers (Figure 1). Plots were 3ft x 5ft in size and replicated four times. Treatments were applied four times prior to initiation of drought, 6/11, 6/25, 7/9, 7/23 with a fight application made post drought during recovery on August 5th 2024. Drought stress was initiated on July 15th 2024 and completed on July 29th 2024 with no water being applied and the overhead canopy blocking any rainfall from occurring during this time.

Data were  collected  for various indicators of turf health, including color, quality, normalized difference vegetation index (NDVI), and volumetric water content. Plots were replicated four times, as shown in Figure 1.

Figure 1: Plot plan for Columbus Biological trials

During the trial, color ratings were taken on a 1-9 scale, with 6 indicating acceptable quality. NDVI data and images were collected weekly using an NDVI camera, focusing on stress levels (% of turf stressed) and turf quality, particularly voids and loss of density (1-9 scale, with 6 = acceptable). During the dry-down period, soil moisture readings (% volumetric water content) will be taken using Spectrum Technologies’ TDR 300. Post drought recovery was initiated through reapplication of water which begun on July

Soil samples will also be collected at various stages of application and drought stress to assess the impact of water deficit and recovery periods. The focus will be on determining the persistence of applied biological treatments within different turfgrass soil types and communities.

All data were analyzed using SAS 9.4 with means separation carried out at p=0.05.

Results:

The 2024 trial has shown once again a somewhat different set of results compared to the 2022 and 2023 data.

Color rankings were found to be significantly higher for the Griggs Bros and Harrells products compared to the Cytogro, UTC and higher rate of Urea (Figure 2)

Figure 2. Average color rankings for treatments used in biostimulant trial exposing turfgrasses to drought in Columbus OH, Summer 2024

NDVI rankings followed a somewhat similar pattern with Griggs products providing significantly higher ratings than the Untreated check, Progressive Turf Greater Green and Cytogro.

Figure 3. Average NDVI ratings for treatments used in biostimulant trial exposing turfgrasses to drought in Columbus OH, Summer 2024

Quality ratings did not agree with the initial data however as Foliar Pak was found to provide higher quality ratings (1-9 scale) throughout the trial compared to 6 of the other treatments. Only the two rates of Urea were found to be within statistical significance to the Foliar Pak treatment (Figure 4).

Figure 4. Average quality ratings for treatments used in biostimulant trial exposing turfgrasses to drought in Columbus OH, Summer 2024

Percent stress showed a broad range of variability and while the untreated check, Progressive  Turf Greater Green and Cytogro trended higher, the amount of variability limited significance being attached to any of the data. Interestingly the Griggs product did have the lowest rating but again this was not significant. (Figure 5)

Figure 5. Average percent stress on plots for treatments used in biostimulant trial exposing turfgrasses to drought in Columbus OH, Summer 2024

Volumetric Water content showed some variability but no single treatment was found to be significantly wetter than another (Figure 6) and a majority of plots by the end of the two week trial were found to be around 10-12% VWC which is extremely low on native soil based greens.

Figure 6. VWC averages two week after water was cutoff for treatments used in biostimulant trial exposing turfgrasses to drought in Columbus OH, Summer 2024

Introduction

Growth regulators for turfgrasses have been in use since the mid-1900’s and have become widely used on golf course putting greens, fairways, and tees. As of 2024 only two major hormonal pathways are being regulated by products labeled for turf, gibberellins (Primo, Trimmit, Anuew, etc.) and ethylene (Proxy). However, auxins are group of hormones that are involved in numerous stress responses and their regulation could improve turfrgass tolerance to a variety of stresses. Synthetic auxins are applied as herbicides (2,4-D, dicamba, etc.) and inhibitors of auxin transport can also regulate growth and stress responses. Chlorflurenol, sold as Maintain CF 125, is an auxin transport inhibitor and one of the oldest commercially available growth regulators.

This product was used to regulate growth of roadside turf in the 1960’s and 70’s, but was used considerably less as gibberellin inhibitors were released into the market. In 2023, researchers from Rutgers University showed that chlorflurenol increased creeping bentgrass tolerance to heat, and becuase auxins are highly involved in tillering, we were interested to see if chlorflurenol increased tolerance to shade. Still, we had no clue how greens or fairway height creeping bentgrass would tolerate chlorflurenol and if it would interact with other standard growth regulators like trinexapac-ethyl. In 2024, we established field experiments in Wooster and in Columbus to see if chlorflurenol could be tolerated by finely cut creeping bentgrass. An experiment was also established on naturally shaded tall fescue to see if chlorflurenol improved shade tolerance.

Materials and Methods

The experiment in Columbus was carried out on a creeping bentgrass putting green (007 XL) and a creeping bentgrass fairway, both maintained with best management practices. Applications of chlorflurenol (Maintain CF 125) and trinexapac-ethyl (T-Nex) were made on 6/28/24, 7/11/24, 7/26/24, and 8/11/24. Chlorflurenol was applied at 10 or 100 micromolar (Figure 1). These two different concentrations are 24x and 240x reduced concentrations relative to the label rate (0.50 gallon per acre). Trinexapac-ethyl was applied at 0.125 fl. oz. / M on the putting green and at 0.250 fl. oz. / M on the fairway. On July 26th photoselective filters were placed on fairway plots to simulate shade from trees to examine if chlorflurenol improves turfrgass growth under shade.

Figure 1: Treatments and rates used

Current results

All experiments we are conducting using chlorflurenol currently indicate that this auxin transport inhibitor is safe to use at low concentrations on low-cut creeping bentgrass and on high-cut tall fescue.

On the other hand, the label rate of Maintain CF 125 and treatments at 1,000 micomolar have shown damage to high-cut tall fescue. The turf recovered, but these higher rate treatments led to severe wilting (though water was not limiting). Thought once recovered, plots treated with these rates performed very well.

The 10 and 100 micromolar rates result in lighter creeping bentgrass color on greens and fairways. Current results also indicate that Poa annua is sensitive to chlorflurenol mixed with trinexapac-ethyl, though long-term control of Poa annua is still unknown. Phytotoxicity is especially noticeable on fairway plots with higher trinexapac-ethyl rates with 10 micromolar chlorflurenol.

Figure 2: Turfrgass quality and NDVI results from Columbus plots.

Figure 3: Light box images of putting green plots taken on 7/26/24.

Figure 4:Light box images of fairway green plots taken on 7/26/24.

While not significant, 100 micromolar chlorflurenol with trinexapac-ethyl (0.125 or 0.250 rates) improves turfrgass quality compared to trinexapac-ethyl alone in both Wooster and Columbus plots (Figure 3 and 4). This combination also seems to suppress growth more and longer compared to trinexapac-ethyl alone, especially on fairways with the higher rate of trinexapac-ethyl (Figure 4). The higher rate of chlorflurenol with trinexapac-ethyl also results in a darker green color compared to trinexapac-ethyl alone, very noticeable in Wooster (Figures 5 and 6).

Figure 5: Drone photo of putting green plots in Wooster on 8/11/24.

Figure 6: Drone photo of fairway plots in Wooster on 8/11/24.

The results of this research is promising. Chlorflurenol is safe at very low rates on putting greens and fairways, and results show that this auxin transport inhibitor can increase color and quality. This plant growth regulator may further suppress growth when combined with a gibberellin inhibitor, and initial results do show that chlorflurenol improves growth of turfgrasses growing under shade. Further research is needed on different rates, combinations with other pesticides and growth regulators, and other auxin transport inhibitors that are formulated as pesticides such as NPA.

T. Hicks Dept Plant Pathology

Fungicides trials for 2024 include work on fairway height turf, potential new molecule technology that could be added to treatments and evaluation of options for brown patch Rhizoctonia solanii control. All material is labelled as per agreed with industry partners and trials are laid out as per below.

Location of each trial on rows 2 and 5