Golf Course Management

JUN 2019

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70 GOLF COURSE MANAGEMENT 06.19 Percentage volumetric water content at a soil depth of 3 inches for Princess 77 bermudagrass 2014 2015 2016 ETos ETos ETos Chemical 50% 65% 80% 50% 65% 80% 50% 65% 80% Control 11e† 15cd 16cd 20e 28d 30cd 18g 21fg 34abc TE 13de 16bcd 20a 20e 34bcd 36abc 25def 24efg 36a Surfactant 14de 15d 19a 27d 30cd 39ab 22efg 30bcd 35ab TE+surfactant 11e 18abc 19ab 20e 37ab 41a 28cde 32abc 34abc † Values within a column followed by the same letter (separately for each year) are not significantly different. Table 1. Volumetric water content (%) at soil depths of 0 to 3 inches (0 to 7.5 centimeters) in 2014, 2015 and 2016 for Princess 77 bermudagrass [Cynodon dactylon (L.) Pers.] ir- rigated at either 50%, 65% or 80% of ETos and treated monthly with either trinexapac-ethyl (TE) (Primo Maxx, Syngenta), a surfactant (Revolution, Aquatrols; the surfactant is a modified methyl-capped block copolymer), a combination of trinexapac-ethyl + the surfactant, and a nontreated control. Values represent an average of 25 data points and are pooled over five sampling months (June to October). Plots receiving trinexapac-ethyl or the combination of Revolution and trinexapac- ethyl and irrigated at either 65% or 80% ETos exhibited turfgrass quality ratings of 6 or greater throughout the research period (Fig- ure 4). Bermudagrass treated with Revolution alone exhibited greater quality when com- pared with controls in June and July at 65% ETos and from June to November at 80% ETos (Figure 4). Soil volumetric water content and volumetric water content uniformity „e application of Revolution alone in- creased soil moisture levels in plots irrigated at 50% ETos in 2015 (Table 1). Plots irrigated at 65% ETos and treated with both Revolu- tion and trinexapac-ethyl had higher volumet- ric water content than control plots during all three experimental years (2014, 2015 and 2016). „e combination of Revolution and trinexapac-ethyl also increased soil moisture levels at 80% ETos in 2014 and 2015. Trinexa- pac-ethyl alone influenced volumetric water content only in 2014 at 80% ETos. When data were averaged over all ETos levels, sam- pling months and years, volumetric water con- tent was greater in plots treated with trinexa- pac-ethyl (26.2%), Revolution (26.3%), and trinexapac-ethyl + Revolution (27.4%) than in the control plots (21.2%). With the exception of plots irrigated at 80% ETos in 2015, bermudagrass plots receiv- ing Revolution in combination with trinexa- pac-ethyl exhibited greater soil moisture uni- formity compared to untreated controls at all irrigation levels throughout the research period. Standard deviation (used to calculate moisture uniformity) values on plots treated with Revolution + trinexapac-ethyl ranged from as low as 2.2 for 65% ETos in 2014 to as high as 4.6 for 65% ETos in 2015. Soil mois- ture uniformity was lower on the control plots and ranged from 3.4 for 65% ETos in 2014 to 6.8 for 65% ETos in 2015. Plots receiving Rev- olution alone had a more uniform volumetric water content compared to the untreated con- trols throughout the research period for all ir- rigation levels except for 65% ETos in 2014 and for 50% and 80% ETos in 2015. Simi- larly, the application of trinexapac-ethyl alone resulted in a more uniform moisture distribu- tion throughout the investigative period with the exception of plots irrigated at 80% ETos in 2015 and at 50% ETos in 2016. Conclusions Our results indicate that the use of a plant growth regulator or a surfactant, or the com- bination of both is an effective drought man- agement strategy that helps conserve water without a significant loss of quality of the turf stand. Applying a combination of surfactant and trinexapac-ethyl allowed us to irrigate bermudagrass at 50% ETos and still main- tain acceptable quality and dark green color. Our results indicated that applying a tank mix of trinexapac-ethyl and Revolution and, to a lesser extent, applying the two products sepa- rately led to acceptable turfgrass quality (6 or better on a scale of 1-9, where 1 is dead grass and 9 is turf of the highest quality) for the ma- jority of the growing months throughout the three years of the study. Our studies did not include physiological measurements, but soil moisture measure- ments indicated that loss in soil water con- tent was reduced only when trinexapac-ethyl was applied in combination with Revolution. „e effects of trinexapac-ethyl alone on soil moisture and water use have been extensively studied for cool-season grasses with conflict- ing results. Our VMC results do not indicate a difference in soil water loss or water use be- tween the untreated bermudagrass and the bermudagrass treated with trinexapac-ethyl. Applying only Revolution did not lead to consistent or significant increases in volumet- ric water content at the two lower irrigation levels. However, when Revolution was ap- plied in combination with trinexapac-ethyl, volumetric water content increased in plots irrigated with as little as 50% ETos in 2015 and in plots irrigated at 65% ETos through- out the three-year research period. Although volumetric water content was not consistently enhanced by all treatment combinations, ap- plications of Revolution, trinexapac-ethyl, and a combination of both resulted in increased volumetric water content uniformity and ap- parently greater irrigation use efficiency. Our study documented that bermuda-

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