Date of Award
Doctor of Philosophy (PhD)
Plant and Environmental Science
Lambert B. McCarty
Copper (Cu) is an often-seen component in various turf industry products including fungicides, algaecides, and colorants. Though an essential micronutrient in plants, excessive levels of Cu has been shown in various plant commodities to cause phytotoxicity and plant death. With the increasing use of pigments on hybrid bermudagrass [Cynodon dactylon (L.) Pers x. C. transvaalensis Burtt-Davy] putting greens to replace overseeding practices during traditional dormant periods combined with regular applications of fungicide, algaecide and spray additives containing Cu, the objective of this study was to investigate the potential impact of individual and combined copper-containing treatments on hybrid bermudagrass and possible remediation options for turfgrass managers dealing with toxic levels of Cu in soil.
A turf colorant, fungicide, and algaecide were selected for testing alone and in combination for 13-week field trials conducted in 2019 and 2020 on hybrid bermudagrass prior to, and during, Spring transition: PAR (copper phthalocyanine pigment), Junction DF (copper hydroxide + mancozeb), 0.25 ppm and 2.0 ppm copper sulfate (CuSO4) by volume, PAR + 0.25 ppm CuSO4, PAR + 2.0 ppm CuSO4, Junction DF + 0.25 ppm CuSO4, Junction DF + 2.0 ppm CuSO4, PAR + Junction DF + 0.25 ppm CuSO4, and PAR + Junction DF + 2.0 ppm CuSO4. All treatments were also used in two separate greenhouse studies, in addition to weekly PAR, 50, 100, and 200 ppm by volume of CuSO4 treatments, investigating levels of Cu necessary to negatively impact the growth of hybrid bermudagrass.
In field trials, treatments containing the colorant PAR exhibited limited increases in turf quality, normalized difference vegetative index, and coverage compared to other treatments. In field trials, turf areas treated with PAR alone experienced the worst change of turf quality over time with an average change of -0.0453 and 0.2157 per week in studies one and two, respectively. Applications of Junction DF resulted in net soil Cu concentrations exceeding non-Junction treatments in studies one and two with applications of PAR + Junction DF resulting in statistically higher net Cu concentrations in soil each year of 7.846 and 4.511 kg Cu ha-1. In greenhouse trials, irrigation treatments containing 50, 100, and 200 ppm CuSO4 had the greatest impact on turf measurements with turf quality decreasing in 2022 study at rates of -0.1054, -0.1631, and -0.2585 per week, respectively. The continual application of PAR, alone or in combination, resulted in decreases of phytotoxicity over time in both greenhouse studies except for PAR + Junction DF and PAR + Junction DF + 2.0 ppm CuSO4 in 2022 study. Applications of Junction DF, alone or in combination, resulted in leaf tissue concentrations of copper exceeding concentrations of 50 ppm CuSO4 treated pots which averaged 544 mg Cu kg-1 leaf tissue concentration in 2020 greenhouse study and greater than 316 mg Cu kg-1 in 2022 tissue concentration with irrigation treatments of 200 ppm CuSO4. Results of field and greenhouse studies suggest labeled rates of Cu-containing products should not cause decreases in turf quality or appearance initially, however, continued use of products may lead to excessive Cu concentrations over time.
In soils, Cu adsorbs tightly with organic matter and clay soil particles resulting in potentially excessive accumulation in thatch layers and native soil turf areas. To test where (depth) Cu may accumulate in soil and if soil Cu could be displaced with various compounds, greenhouse pot plugs were obtained from a 1-year-old renovated hybrid bermudagrass research green built to USGA specifications. Plugs were treated over 13 weeks with previously listed greenhouse study treatments and Cu concentrations were measured in thatch layers, 0 – 2.54 cm below thatch, and 2.54 – 5.08 cm below thatch for all pots. The thatch layer contained the greatest amount of copper with 635 kg Cu ha-1 compared to subsequent two layers with 11.26 and 6.84 kg Cu ha-1, respectively. This suggests mechanical removal of thatch layer could reduce overall soil Cu concentration. However, mechanical removal of thatch and subsoil leads to temporary decreases in aesthetic and playability of turf surfaces, rendering these methods as potentially unacceptable for some turf managers. The use 1 N ammonium sulfate ((NH4)2SO4) (AMS) solution, 1 N calcium nitrate ((Ca)(NO3)2) solution, 1 N gypsum (CaSO4•2H2O), and tap water were investigated for potential to leach Cu from soil treated with 1,000 ppm Cu-CuSO4. Exposure to 1 filtration of AMS resulted in the removal of approximately 2,064 mg Cu kg-1 which was similar or greater than all of treatments cumulative effects after four filtrations. Results suggest ammonium sulfate may render Cu into a soluble state allowing for its removal from root zone sites in areas where mechanical removal of thatch is not possible.
Visual characteristics for turf quality were not consistently impacted negatively by any products applied at industry labeled rates and timings in individual studies, though early evidence indicates the potential for excessive accumulation of Cu when applied frequently. In situations of excess Cu concentrations, soil flushes with AMS may serve to facilitate leaching of Cu ions from rootzone in areas where mechanical removal is not possible. Identification of minimal AMS quantity necessary for efficient Cu flushing and irrigation requirement should be focus of future investigation in addition to identifying soil adsorption potential of copper species in USGA and native soil greens.
Gore, Adam, "Impact of Copper-Containing Products and Irrigation On Hybrid Bermudagrass (Cynodon Dactylon (L.) Pers X C. Transvaalensis Burtt-Davy)" (2023). All Dissertations. 3506.