Is the grass really greener?

Pigmented products provided inconsistent health benefit.

Bert McCarty, Ph.D.; A.W. Gore; and J.R. Gann

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Table 1. Products and rates used in 2011 to determine whether pigment-containing products reduce summer heat stress on creeping bentgrass.

The golf course industry is constantly evolving, developing products to improve health and competitive benefit to turfgrasses that are often grown outside their naturally adapted regions. For example, various traits such as low mowing-height tolerance and excellent stand density have encouraged turf managers to establish cool-season turfgrasses in hotter and more humid climates (4). However, issues often arise during stressful summer conditions, resulting in a lowering of quality in what is referred to as summer bentgrass decline (1,2). As a result of this increased summer stress, some recently developed turf products contain various pigments, dyes, paints and other components to assist in summer stress relief on cool-season greens and to speed spring green-up of warm-season grasses.

Pigments and turf

For turf managers, pigments serve an additional purpose by masking various imperfections and inconsistencies, creating a more aesthetically pleasing turfgrass surface. However, frequent use of pigments may alter the reflection, transmission and absorption of light within the turfgrass canopy, reducing the level of photosynthetically active radiation required for photosynthesis and thus decreasing turf quality over time (6).

Pigments consist of dry powders whose chemical composition depends on the specific color desired. White pigments are commonly composed of titanium dioxide (TiO2), whereas blue pigments contain phthalocyanine (a copper-based compound) and green pigments consist of a more stable, chlorinated form of phthalocyanine (6).

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Applications were made every 14 days.
Applications received a potassium supplement using Stress Relefe (0-0-25) (Harrell’s LLC) at 4 ounces/1,000 square feet (12.6 liters/hectare).

Table 2. Products and rates for 2013 and 2014 greenhouse and growth chamber trials to reduce summer stress of creeping bentgrass and improve winter survival of hybrid bermudagrass.

Previous research has demonstrated that combination products of aluminum tris + mancozeb with Pigment Blue 15 improve turf quality and color greater than combinations of aluminum tris + mancozeb lacking Pigment Blue 15 (3). The activity of aluminum tris + mancozeb appears to be synergistically enhanced by Pigment Blue 15. In combination with the introduction of several pigmentcontaining products, the potential for paints and pigments to improve turfgrass health and mask symptoms of decline has since generated increased interest.

Reported research supporting this interest is limited, especially on creeping bentgrass (Agrostis stolonifera L.) putting greens grown under stressful conditions. The objective of the research was to evaluate the ability of such products to relieve summer stress on creeping bentgrass and to promote spring recovery of TifEagle bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy] in the hot, humid southeastern United States.

Materials and methods

Field trials

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Figure 1. Bentgrass turf response to foliar application of various paints and pigments. Note the range of color products produced on turfgrass surface during typical summer stress.
Photo by J. Gann

Over the past several years, field research has been conducted at Clemson University in South Carolina on 12-year-old Crenshaw creeping bentgrass and TifEagle bermudagrass putting greens built to USGA specifications. Previous research at Clemson University focused on the effects of pigmented products (Table 1) on creeping bentgrass in regard to reducing the effects of summer heat stress (5). Additional research on this topic was initiated in the summer of 2013 and expanded to include the effects on winter survival of hybrid bermudagrass as well as a new collection of potential products (Table 2).

Product applications in the initial study began on June 18, 2011, and were made weekly through Sept. 3 at the products’ labeled rates at the time of application. Applications were made with a carbon dioxide (CO2)-powered backpack sprayer delivering 20 gallons/acre (187 liters/hectare). Plots were arranged in a randomized complete block design and were 6.5 feet × 10 feet (2 meters × 3 meters) in size with treatments replicated four times. Research sites were maintained to normal putting green standards with daily mowing heights of 0.125 inch (3.2 millimeters), irrigation applied as needed to prevent wilt, fertilization with 6 pounds nitrogen/1,000 square feet (29 grams nitrogen/square meter) yearly and treatment with fungicides as needed to minimize disease pressure.

Visual quality and normalized differential vegetative index (NDVI), an electronic measurement of “green” tissue, were assessed twice weekly. Daily measurements included canopy temperature using a handheld infrared thermometer, chlorophyll content with a handheld chlorophyll meter, and soil moisture using an electronic probe, with all measurements taking place one hour after solar noon. Carbon dioxide exchange ratios were measured twice weekly using a CIRAS-II Portable Photosynthesis System as well as photosynthesis (light efficiency or fluorescence) with a FluorPen FP 100. Carbon dioxide exchange rate measures the net CO2 exchange between the surface of the turfgrass and the atmosphere. A positive measurement indicates respiration exceeds photosynthesis, whereas a negative measurement results if photosynthesis exceeds respiration. Root weight as well as soil and tissue nutrient analyses were conducted at the initiation and completion of the studies.

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Values in a column not followed by the same letter are significantly different.
Abbreviations: NDVI, normalized differential vegetation index; CER, carbon dioxide (CO2) exchange rate.

Table 3. 2011-2013 field trial evaluating pigment-containing products to reduce summer heat stress on creeping bentgrass.

Growth chamber studies

In addition to field trials, growth chamber studies were conducted to evaluate treatments in a controlled, stressful environment. Plugs 4 inches (10.16 centimeters) in diameter and 4 inches deep were removed from research greens and placed in 6-inch (15.24-centimeter) diameter × 12-inch (30.48-centimeter) deep pots filled with an 85:15 sand/peat rootzone mix. Plugs were established to fill pots and were placed in growth chambers at temperatures stressful for turfgrasses — higher (95 F [35 C]) temperatures for bentgrass and colder (23 F [-5 C]) temperatures for bermudagrass. In addition, an unstressed, untreated control remained in a normal greenhouse environment. All pots received 3.4 ounces (100 milliliters) of tap water every three days. Carbon dioxide exchange ratios and fluorescence measurements were taken every other day for the duration of these studies.

Light transmitted to the turf

To determine product effects on the quantity and quality of light reaching the turfgrass canopy, products were applied to transparent acrylic sheets 10 × 8 inches (25 × 20 centimeters) using a spray chamber calibrated at 20 gallons/acre (187 liters/hectare) to deliver the application rates listed in Table 1. Once dried, acrylic sheets were individually placed on the surface of a custom-made cardboard box 7.87 × 9.44 × 9.84 inches (20 × 24 × 25 centimeters) tape-sealed to block all light except that transmitted through the acrylic sheet. Photosynthetic active radiation intensity (μmol/ square centimeter/second of transmitted light integrated between 400 and 700 nanometers) and spectral distribution (~400 to 1,100 nanometers) of transmitted light was measured with an LI-1800 Portable Spectroradiometer. Measurements were taken outdoors on cloudfree days at solar noon, which ranged from 1300 to 1400 hours during summer months. Measurements were repeated on four separate days.

Leaf penetration

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Figure 2. Spectroradiometer data indicating wavelength intensities following applications of various pigments and paint to transparent acrylic sheets.

In an auxiliary study, PAR and Turf Screen were investigated to ascertain whether or not products penetrated treated leaves or remained on the leaf surface. Both products were diluted to respective field solutions and applied evenly to grass blades with the tracer dye, isothiocyanate. Treated plants remained in the greenhouse for 48 hours before being clipped then imaged using a Confocal Imaging System at 20× magnification with data used to create 3-D renderings of the leaf.

Results

Canopy temperature

Turf color response following application of various products is shown in Figure 1. When evaluating canopy temperatures following application, in most instances, tested products did not lower canopy temperatures compared to the untreated control (Table 3). On many rating dates, treated turf actually exhibited higher temperatures compared to the untreated control. Among products, Turf Screen, PAR and Foursome had similar summer temperatures, which averaged 1.5 F higher than the untreated control (104 F [40 C]) in both studies, whereas the paint exhibited an extremely high average of 110 F (43.3 C) in study 1. In study 2, Turf Screen, PAR and Foursome had similar average temperatures of 105.5 F (40.8 C), which averaged 1.4 F higher than the untreated control (104.1 F or 40.1 C), whereas the paint treatment again had the highest average at 110 F (43.3 C).

Turf quality and NDVI

Visual quality of turf treated with Turf Screen, PAR and Foursome was statistically similar to the untreated control in both studies (Table 3). Turf treated with paint had lower quality over the course of the summer in both studies, with averages of 5.1 and 4.4 compared to 7.0 and 6.2 for the untreated control. Differences were observed between the two studies. Study 1 had higher initial turf quality, resulting in turf quality treatment averages of 7.0 for the untreated control, 7.0 for Turf Screen, 6.9 for PAR and 7.1 for Foursome. In study 2, turf quality averages were 6.2 for the untreated control, 6.5 for Turf Screen, 6.0 for PAR and 6.1 for Foursome.

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Figure 3. Confocal microscopy projection image (20×) of Turf Screen on creeping bentgrass leaves with colors indicating a definitive line between the product (red) and the leaf surface (green). This suggests Turf Screen covers the leaf surface, including stomata, resulting in decreased moisture and gas exchange capacity leading to increased surface temperatures and/or reduced photosynthesis.
Photos by J. Gann

The untreated control had a significantly higher NDVI (natural “green” color) than PAR, Turf Screen and the commercial paint throughout the summer. Differences were not observed among Turf Screen, PAR and Foursome in either study. The paint always produced significantly lower values, with an average ratio of 0.65 compared to the untreated control at 0.74. In study 2, NDVI values were similar for the untreated control, Turf Screen and PAR treatments.

Carbon dioxide exchange rate

In study two, the CO2 exchange rate (-0.059 µmol CO2/square centimeter/second) was lower in untreated turf than in all treated turf, indicating treatments reduced net photosynthesis (Table 3). In both studies, the commercial paint had the highest CO2 exchange rate (0.323 and 0.216 µmol CO2/square centimeter/second). Turf Screen and PAR performed similarly in both studies (0.182 and 0.118 µmol CO2/square centimeter/second in study 1, 0.090 and 0.091 µmol CO2/ square centimeters/second in study 2). During July when temperatures were highest, the untreated control exhibited significantly lower CO2 exchange rate values (0.151) than PAR (0.341), Turf Screen (0.327) and the paint (0.477) in study 1 and significantly lower CO2 exchange rate values (0.044 µmol CO2/square centimeter/second) than all other treatments in study 2. Growth chamber experiments did not consistently show statistical differences among untreated and treated pots, indicating treatments did not improve or lessen turfgrass tolerance to environmental stresses.

Fluorescence

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Figure 4. Confocal microscopy projection image (20×) of PAR on creeping bentgrass leaves. Dispersion of colors indicates PAR (red) actually entered the leaf (green) and may have interfered less with stomatal conductance.

Differences were not detected between untreated and treated plots during study 1(Table 3). All treatments in study 2 exhibited a general increase in photosynthetic efficiency, with Turf Screen exhibiting a significantly better rate. Inconsistency among treatments shows that none of the pigmented products provided any type of consistent relief during the heat of summer. Similar observations were made in the growth chamber studies with only the unstressed control having a significantly greater photosynthetic efficiency.

Soil and tissue analysis

Tissue and soil analyses were conducted because of the metallic (zinc and copper) contents of the products and their potential toxicity to plants (Table 3). In both studies, Turf Screen treatments were significantly higher in zinc concentration than all other treatments, with an average 911 ppm compared to 88 ppm for the untreated control. In regard to tissue copper concentrations, the paint was consistently higher with an average of 155 ppm compared to the other treatments, which averaged 61 ppm.

After repeated applications, only the Turf Screen treatment exhibited higher zinc concentrations in soil than the other products. However, concentrations were not believed to exceed levels that would be considered toxic to plants.

Root weight

No effect of treatments on root weights occurred at the end of field studies (data not shown).

Light quality and microscopy imaging

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Figure 5. Extensive use of pigment products containing heavy metal appear to have led to heavy metal accumulations in this field sample. The accumulations may decrease soil drainage and/or proper air exchange.
Photo by B. McCarty

With little positive influence on reducing temperatures and increasing CO2 exchange rates, additional research was performed on product effects on light quality and leaf penetration. Spectroradiometer data indicated a reduction in photosynthetically active radiation (μmol/square centimeter/second integrated from 400 to 700 nanometers) when products were applied to transparent acrylic sheets (Figure 2). The copper-based pigments Foursome and PAR reduced photosynthetic active radiation transmission by 19% and 21%, respectively. Even greater reductions were observed with Turf Screen (39%) and the commercial paint (46%).

In an attempt to better understand how well products penetrate treated leaves, microscopic imaging was performed. The interaction between applied products and leaf blades indicated Turf Screen remained mostly on the plant surface (Figure 3), and in some cases covered stomata, whereas PAR actually entered the leaf (Figure 4). Coated stomata may increase leaf temperature as transpiration is reduced and could potentially reduce photosynthetic efficiency as gas exchange is impeded. This partially explains field and growth chamber results where treated turfgrass often had higher leaf surface temperatures and/or reduced photosynthesis.

Conclusion

While the idea of applying pigmentcontaining products to assist in relieving summer heat stress on creeping bentgrass is desirable, results from this research do not consistently support their use in areas such as the hot, humid southeastern United States. After application, these products often provide a temporary visually appealing green color that masks imperfections on the turfgrass surface. In reality, long-term continued application of many of these products may actually have a negative effect on the turfgrass such as increasing surface temperatures and decreasing carbon-dioxide exchange (photosynthetic efficiency).

The influence of these products on winter hardiness of hybrid bermudagrass putting greens is still under investigation. As photosynthetic properties of bermudagrass (a warmseason [C4] turfgrass) are different from those of bentgrass (a cool-season [C3] turfgrass), we cannot assume pigment-containing products have similar effects on bermudagrass based on results obtained through studies of creeping bentgrass.

Turfgrasses almost always exhibit certain levels of stress, especially when grown outside of native environments. For now, superintendents are better served by adhering to traditional practices of proper aerification, fertilization and watering of putting greens. It has also been noticed that extensive use of products containing heavy metals appears to lead to accumulation of these metals in the upper soil surface (Figure 5), raising concerns that overapplication of these products may negatively influence the chemical and physical properties of soils.

Further research on both bentgrass and bermudagrass commenced in summer 2013 and is ongoing with a greater selection of products (Table 2). Applications were made every two weeks at current labeled rates with the initial application to bentgrass made on June 24, 2013, and with final data collection on Sept. 24. All measurements from the previous field trial studies were repeated in 2013. Similar treatments were made in fall 2013 to hybrid bermudagrass greens to ascertain winter survival following treatment. This experiment is ongoing and will be covered in a subsequent article.

Readers are reminded this research was conducted in the hot, humid southeastern United States and may not be applicable to other areas.

Funding

Funding for this research was provided by the senior author and Clemson University Public Service Activities.

Acknowledgments

Appreciation is extended to Drs. Christina Wells, Terri Bruce and Patrick Gerard for their technical assistance.

Literature cited

  1. Beard, J.B. 1997. Dealing with heat stress on golf course turf. Golf Course Management 7:54-59.
  2. Lucas, L.T. 1995. Update on management of summer decline of bentgrass. 66th Annual Michigan Turfgrass Conference Proceedings 25:111-112.
  3. Lucas, L.T., and L.C. Mudge. 1997. Fungicidal compositions for the enhancement of turf quality. U.S. Patent 5 643 852. Date issued: April 3.
  4. McCarty, L.B. 2011. Best Golf Course Management Practices. 3rd ed. Prentice-Hall, Upper Saddle River, N.J.
  5. McCarty, L.B., J.R. Gann, C.E. Wells et al. 2013. Physiological responses of creeping bentgrass to pigment containing products. Agronomy Journal 105:1797- 1802.
  6. Reynolds, W.C., G.L. Miller and T.W. Rufty. 2012. Athletic field paint impacts light spectral quality and turfgrass photosynthesis. Crop Science 52:2375- 2384.

Bert McCarty is a professor, A.W. Gore is a graduate research assistant and J.R. Gann is a research specialist at Clemson University, Clemson, S.C.