February 2017

SportsTurf provides current, practical and technical content on issues relevant to sports turf managers, including facilities managers. Most readers are athletic field managers from the professional level through parks and recreation, universities.

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Page 12 of 51 February 2017 | SportsTurf 13 2 pounds manganese sulfate/A applied monthly. Fungicide treated plots were sprayed with Velista (a.i. penthiopyrad) at 0.7 oz/1000 ft2 immediately after fraze mowing and again on 14 October 2015. Treatments were immediately watered in with 0.2 inches of post-application irrigation. SDS severity and green cover were evaluated every 7 days by visual estimation of percent disease area and digital image analysis, respectively, in Spring 2016. Area under the disease progress curve (AUDPC) was calculated with the trapezoidal rule. All data were subjected to analysis of variance, and where applicable, means were separated with Fisher's Protected LSD (0.05). FINDINGS Trial 1: Fraze mowing at either 0.16 or 0.32 inches did not statistically increase or decrease SDS severity in Spring 2015 compared to the initial rating. Plots treated with ammonium sulfate had lower SDS severity than urea on two of the four rating dates, reducing disease by 12-22% from the initial 2014 rating. Over the initial season of study, fraze mowing did not increase or reduce an established SDS epidemic. Even after year two, results for this smaller initial trial were inconclusive. Trial 2: Fraze mowing at 0.32 inches alone and in combination with other treatments decreased SDS severity compared to non-fraze plots. Fraze mowing breaks up the thatch and mat layer, allowing new growth of rhizomes and stolons to occur. This new plant tissue should be pathogen free, and if protected from new infection should lead to recovery. The evaluation of various nitrogen sources (calcium nitrate or ammonium sulfate) in this study was aimed at manipulating soil pH, which has been observed to play a role in the reduction of SDS. When ammonium (positively charged) is absorbed by plants, hydrogen ions are released in the rhizosphere; therefore, creating a more acidic environment near the roots. When nitrates are absorbed by plants, the exchange is with hydroxyl ions; therefore, raising the pH to a more basic environment. In most research, lowering the pH with an ammonium fertilizer source has subsequently reduced SDS severity. Figure 1.* Effect of fraze mowing height and nitrogen source on SDS severity. In this trial, sprayable ammonium sulfate reduced SDS severity in the unfrazed plot compared to calcium nitrate, but no significant differences were noted among fraze mowed plots (Figure 1). In a previous trial (Cottrill et al. 2016) at the site, ammonium sulfate did not reduce SDS on plots that did not receive aerification or fraze mowing. This seems to support the theory on acidic rhizosphere conditions immobilizing SDS, and the potential need to integrate ammonium fertilization with an aerification or thatch removal practice such as fraze mowing. Manganese is a micronutrient needed for enzymes involved in the lignification of cell walls, a defense mechanism against diseases. Previous work has shown that the take- all patch pathogen (another soilborne disease) changes the form of manganese to make it unavailable to the plant root. This manganese deficit results in the plant being susceptible to infection. In these cases, and particularly in high pH or manganese deficient soils, supplemental manganese applications have resulted in lower disease severity not just for take-all patch, but also for summer patch on Kentucky bluegrass. After the first year of applications, manganese did not have an impact on SDS severity, so perhaps this mechanism is not the same. Treatments continued into the second season and will be evaluated.

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