Soil Surfactant and Fungicide Influence on Soil Moisture, Disease Presence and Quality of ‘Champion’ Ultradwarf Bermudagrass Grown on a USGA Specified Constructed Rootzone in South Carolina, U.S.A

Rationale & Objective. In South Carolina, USA, ancillary observations in a fungicide efficacy trial suggested that certain fungicides influenced turf quality and localized dry spot (LDS) development, but warranted further study to quantify the relationship. Surfactants improve turf quality by promoting more uniform water distribution, and presumable more uniform water and nutrient uptake. Indirectly this would be expected to have a positive effect on plant health and disease tolerance. The objective of this experiment was to determine the relationship of commonly used surfactants and fungicides on affecting the longevity of the fungicide response, soil volumetric water content, and turf quality. Methods. Experiments were conducted during the 2008 and 2009 summers on an USGA specified constructed rootzone research green with established ‘Champion’ ultradwarf bermudagrass. Grass was subjected to three treatments of two factors: surfactant (water control, and two surfactants), and fungicide (water control, four fungicides applied as a program, and one single chemistry). Irrigation was maintained at 75% ET with further reductions as needed to induce stressed conditions. Results. Symptoms of two pathogens were visually determined: Bipolaris spp. (leaf blotch) and Sclerotinia homoeocarpa (dollar spot). In 2008, fungicides influenced disease after the first application with the Program resulting in the least disease severity with Fore having more than the Program, but usually less than the control. In addition, applying a surfactant resulted in less disease than the the water control. In comparison to the the 2008 experiment, disease was documented only twice during 2009. On both dates fungicides and surfactants performed similar to what was found in 2008. Only in 2008 did fungicides consistently influence quality with the program approach resulting in a consistent, higher quality bermudagrass. Both fungicide and surfactant treatments reduced LDS compared to the water controls. Once water stress conditions were induced, soil VWHC was greater in surfactant treated bermudagrass compared to the untreated bermudagrass in both years. Fungicides did not influence soil volumetric water holding capacity. Conclusions. Applying fungicides did increase turf quality and lower LDS, while surfactants increased turf quality, lower LDS, and increase Soil VWHC. However, with one rating exception, there was no evidence of a surfactant and fungicide interaction to enhance quality, lower disease severity and LDS, or increase soil VWHC.