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.
Issue link: http://read.dmtmag.com/i/775572
12 SportsTurf | February 2017 www.sportsturfonline.com FIELD SCIENCE S pring Dead Spot (SDS) is a problematic disease of bermudagrass sports turf managers have dealt with for many years. SDS is the most severe pest issue on bermudagrass in Missouri, and other regions where bermudagrass goes into dormancy. SDS is caused by a soilborne pathogen (Ophiosphaerellaspp.) that infects roots, rhizomes and stolons as the plant goes into dormancy in the fall. During spring green-up, infected patches are dead and simply appear to remain dormant. Recovery can occur from the uninfected areas around those patches by shooting out rhizomes and stolons and oftentimes weed emergence in the affected areas occurs before complete recovery. Since the pathogen is soilborne, control is difficult, particularly in a curative situation. Current control recommendations rely almost exclusively on fungicide use. The effectiveness of these fall preventive applications can be sporadic, and recovery from an existing epidemic may be a multi-year process. Integrating cultural practices with fungicide use may be a method to reduce disease. Observations indicated that newly established bermudagrass would not show signs of SDS until usually the third or fourth season. Additionally, high use areas, such as between the hash marks on football fields, often showed less spring dead spot severity than low traffic areas. This indicated thatch was perhaps a factor in SDS development so recommendations included thatch management by means of vertical mowing and aeration. The common practice for those who had the disease visible during spring green-up was to rake out the spots and fertilize to promote regrowth and recovery of the bermudagrass. Several research trials have indicated hollow-tine aerification or other cultivation methods may reduce SDS severity and increase fungicide efficacy. Recently, a new intense surface cultivation method termed "fraze mowing" gained popularity as a method of thatch removal and playing surface renovation in sports fields. The key to fungicide efficacy for SDS is to get the fungicide where it is needed. Therefore, the objective of this research is to determine the impact of fraze mowing on SDS severity, and determine how this practice can be implemented in an integrated pest management plan for this disease. METHODS Trial 1 was initiated on 22 July 2014 at the MU Turfgrass Research Farm on a 'Riviera' bermudagrass block severely infested naturally with SDS caused by O. herpotricha. Plots were 5 x 10 feet and arranged in a randomized complete block with four replications. Treatments were arranged in a split plot design with fraze mowing as the main plot and nitrogen source as the subplot. Before treatments were applied, an initial disease rating was conducted on 24 June 2014 to assess treatment effects. Fraze mowing was conducted on 22 July 2014 at 0.16 and 0.32 inches with a KORO Field Topmaker or not cultivated. To encourage bermudagrass regrowth, ammonium sulfate or urea was applied weekly at 0.5 lb N/1000 ft2 for 6 weeks after fraze mowing. SDS severity and green cover were evaluated every 14 days by visual estimation of percent disease area and digital image analysis, respectively. 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). These same plots were fraze mowed again on 30 June 2015 and evaluated for a second season. Trial 2 was initiated on 30 June 2015 at the MU Turfgrass Research Farm on a block of 'Patriot' bermudagrass. The entire 11,000 square foot block was inoculated with a four isolate mix of Ophiosphaerella herpotricha on 13 September 2013. Initial disease symptoms from inoculation occurred in late May 2015. Plots were 5 x 10 feet and arranged in a randomized complete block design with four replications. Treatments were arranged in a split plot design with fraze mowing as the main plot and nitrogen source, manganese, and fungicide application as subplots. Fraze mowing was conducted on 30 June 2015 at 0.16 and 0.32 inches with a KORO Field Topmaker or not cultivated. Dissolved ammonium sulfate or calcium nitrate was applied weekly at 0.5 lb N/1000 ft2 for 6 weeks after fraze mowing. Manganese treatments were applied every other fertilizer application (3 times @ 2 week intervals) as 2 pounds manganese sulfate/A. Nitrogen and manganese treatments continued in summer 2016 with 1 pound N/1000 ft2 and IMPACT OF FRAZE MOWING ON SPRING DEAD SPOT IN BERMUDAGRASS ■ BY BRAD FRESENBURG, PHD, LEE MILLER, PHD & DANIEL EARLYWINE