Biostimulants and their impact on drought stress in Ohio during Summer 2022.
E.J. Nangle1, T Morris1, D.P. Petrella1 S. Cusack2, B. Stith2.
1OSU CFAES Wooster Campus, 1328 Dover Rd, Wooster 44691
2OSU Turfgrass Research Facility, 2710 Northstar Road Columbus OH 43221
Introduction:
Drought stress has become an increased problem for turfgrass managers both in Ohio and across the Midwest with excessively dry periods combined with heat leading to large volumes of water use and concerns about turfgrass quality on high value surfaces. Traditionally golf course superintendents have relied on judicious use of fertility and water management combined with reductions in agronomic inputs to retain turf quality. Recently however with newer turfgrass cultivars emerging for putting greens and ever lower mowing heights there is added pressure to find extra roll and smoothness which has led superintendents to investigate the use of a class of products known broadly as ‘biostimulants’. Further to this, potential changes in legislation may begin to see curbs on pesticide applications. There is a two-fold need then to look more closely at these products and evaluate where they might fit into the golf course managers tool box and also compare these products against what might be considered traditional agronomic practices.
Materials and Methods:
This trial was initiated at the Ohio State University Turfgrass Research Facility in Columbus OH on June 9th 2022. Treatments were then applied on June 23rd, July 7th and July 21st. The trial was placed on a pushup rootzone with mixed annual bluegrass Poa annua creeping bentgrass Agrostis palustris cv. ‘Penncross’ stand. There were eight treatments with four replications, and they are shown in Figure 1. The treatments were laid out in a randomized complete block with dimensions of 0.91m x 1.83m. Treatments were applied using a CO2 backpack sprayer with a carrier volume of 300 L/ha. Treatments were applied for all products at the high label rate (Table 1). Plots were mowed daily at a height of 4.3 mm with clippings collected until the second week of the drought study when plots were only mowed twice.
All areas received current environmental conditions prior to July 13th 2022, with a last wetting agent application made on June 8th and preventative insecticide and fungicide treatments made through out the duration of the trial. On July 12th all supplemental irrigation was removed and a rain out structure was installed to prevent any external rainfall landing on the surface. This allowed for no water to be applied to the research surface for 16 days in total. On July 28th irrigation was applied to a depth of 2.45 cm on all plots and on July 30th irrigation was applied to a depth of 1.25cm.
During the trial color ratings were taken on a weekly basis on a 1-9 scale with 6 = acceptable. Normalized difference vegetation index (NDVI) data were collected as well as images collected using an NDVI camera weekly, stress on the plot (% of turf stressed) and turf quality with voids and loss of density being the main focus (1-9 scale with 6 = acceptable). During the dry down period firmness (depth of penetration in cm) (Spectrum Technologies, Trufirm) and soil moisture readings (% volumetric water content) Spectrum Technologies, TDR 300.
Five days post rewatering turf color, quality, percent stress and NDVI values were collected and analyzed. Data were analyzed using SAS 9.4. Weather data was collected at the site using a Campbell Scientific weather station.
A second trial site in Creston OH at Hawks Nest GC on a creeping bentgrass cv. ‘Pure Distinction’ putting green was run with the same methodology with the only differences being species type, rootzone construction and mowing height on the sites.
Figure 1. Plot layout with treatments and rates for treatments used in a trial evaluating biostimulants and their impact on drought stress in Ohio in the summer of 2022.
| Treatment | 5 Cytogro – .4 Floz/M = 1.1mL/1L |
| 1 Griggs Bros Carboplex 6-4-4 – 6 Floz/M = 16mL/1L | 6 Urea .1N/M = 9g/1L |
| 2 Foliar Pak Foundation Forty 4-0-8 – 3 Floz/M = 7.9mL/1L | 7 Harrells Bio Max Root Enhancer Iron (5%) plus Fulvic Acid – 6 Floz/M = 16mL/1L |
| 3 Plant Food Co. Green T Impulse 6-0-0 – 9 Floz/M = 23.9mL/1L | 8 Untreated |
| 4 Progressive Turf Greater Green 5-0-7 – 12.8 Floz/M = 34.1mL/1L |
Results:
Climatically conditions were both warm enough and dry enough to lead to drought stress occurring on the plots (Figure 2,3 and 4). Of interest was the relative humidity with average numbers at 50% or lower for an extended period during mid – late June (Figure 3).
Figure 2. Daily high temperatures Columbus OH during trial evaluating biostimulants and their impact on drought stress in Ohio in the summer of 2022.
Figure 3. Daily high temperatures in Columbus OH during trial evaluating biostimulants and their impact on drought stress in Ohio in the summer of 2022.
Figure 4. Average daily percent relative humidity in Columbus OH during trial evaluating biostimulants and their impact on drought stress in Ohio in the summer of 2022.
Quality ratings indicated that during the period where there was no limitation on irrigation or rainfall that there was very little difference between treatments. On D28 Urea provided significantly higher quality turf (p=0.05) than a majority of the treatments (Table 1). At D35 when drought stress was initiated urea was again rated amongst the highest treatments along with Harrells BioMax Root Enhancer, Plant Food Co. Green T impulse although only Urea was significantly higher than any of the other treatments (1,2,5,8). Ten days after drought initiation turf was all ratred above acceptable with minor differences being noted. At D52 all treatments showed a decline and only Harrells BioMax Root Enhancer, Urea and Plant Food Co. Green T Impulse were considered above acceptable quality (Table 1). There was no significant difference however between treatments at this time.
Table 1. Daily quality ratings for treatments during trial evaluating biostimulants and their impact on drought stress in Ohio in the summer of 2022.
†Means followed by different letters are significantly different at p=0.05
*Date rainout shelter was installed
Color ratings indicated that through D14 no differences existed while on D21 after initiation Urea rated highest with Harrells BioMax next and all other treatments rated significantly lower (p=0.05). At D35 prior to drought initiation greater variability existed with Urea, Progressive Turf Greater Green and Harrells BioMax providing the highest rated treatments. Only Harrells BioMax and Urea however were significantly higher (p=0.05) than the check plot. Ten days after initiation of the drought all treatments were the same and above acceptable color. D52 the final day of the drought stress showed a decline in some color with four treatments just below acceptable on average while Plant Food Co. Green T, Cytogro, Urea and Harrells BioMax providing turf color above acceptable with all others at or below that rating (Table 2).
Table 2. Daily color ratings for treatments during trial evaluating biostimulants and their impact on drought stress in Ohio in the summer of 2022.
†Means followed by different letters are significantly different at p=0.05
*Date rainout shelter was installed
Evaluations of stress development including wilt, loss of density and color indicated no issues arose until D45 which was 10 days after drought initiation. On that date Foundation 40 rated significantly higher than the Urea plots but not significantly different from any of the rest of the plots. On the final day of the trial Griggs Carboplex had on average 26.9% stress on the plots which was significantly higher (p=0.05) than both Urea and Harrells BioMax treatments (Table 3).
Table 3. Average percent of stress showing on plots for treatments during trial evaluating biostimulants and their impact on drought stress in Ohio in the summer of 2022.
†Means followed by different letters are significantly different at p=0.05
*Date rainout shelter was installed
Firmness data indicated that there were no differences between treatments on the final day of the drought study while some variability existed between treatments in regard to moisture. The untreated check had the lowest moisture ratings along side Progressive Turf treatments while Foliar Pak, Urea and Cytogro were found to have the highest moisture content, and this was significantly higher (p=0.05) than the check and Progressive turf only (Table 4).
Table 4. Volumetric water content and firmness readings on final day of drought study during trial evaluating biostimulants and their impact on drought stress in Ohio in the summer of 2022
†Means followed by different letters are significantly different at p=0.05
Conclusions:
This trial has shown that there is potential for some of these products to offer turf managers help during stressful periods. The application of urea however did act in a comparable manner to many of the treatments which was somewhat surprising. It must be noted of course that the urea rate was marginally higher than many of the treatments but is also an industry standard rate. Drought stress, heat stress and other environmental stresses are going to continue to occur and with greater frequency, turfgrass managers, researchers and companies are going to have to work together to utilize all tools available and thus these products deserve further attention and also different methods of analysis. It is expected this work will continue to run for many summers to come on a range of cultivars and soil types.