Field Quantification of Ammonia Emission following Fertilization of Golf Course Turfgrass in Sub/Urban Areas

Low cost and favorable handling characteristics make urea (46-0-0) a leading nitrogen source for frequent, foliar N fertilization of golf course putting greens in season. Yet few field investigations of resulting NH3 volatilization from putting greens have been directed. Meanwhile, NH3 emissions degrade air and surface water quality. Our objective was to quantify NH3 volatilization following practical, low-N rate, and foliar application of commercial urea-N fertilizers. Over the 2019 and 2020 growing seasons in University Park, PA, USA, an industrial vacuum pump, H3BO3 scrubbing flasks, and sixteen dynamic flux chambers were employed in four unique experiments to measure NH3 volatilization from creeping bentgrass putting greens (Agrostis stolonifera L. ‘Penn G2’) in the 24 h period ensuing foliar application of urea based-N at a 7.32 or 9.76 kg/ha rate. Simultaneous and replicated flux chamber trapping efficiency trials showing 35% mean NH3 recovery were used to adjust NH3 volatilization rates from treated plots. Under the duration and conditions described, 3.1 to 8.0% of conventional urea N volatilized from the putting greens as NH3. Conversely, 0.7 to 1.1% of methylol urea liquid fertilizer (60% short-chain methylene urea) or 0.7 to 2.2% of urea complimented with dicyandiamide (DCD) and N-(n-butyl) thiophosphoric triamide (NBPT) volatilized as NH3.

Creeping Bentgrass Yield Prediction With Machine Learning Models

Nitrogen is the most limiting nutrient for turfgrass growth. Instead of pursuing the maximum yield, most turfgrass managers use nitrogen (N) to maintain a sub-maximal growth rate. Few tools or soil tests exist to help managers guide N fertilizer decisions. Turf growth prediction models have the potential to be useful, but the currently existing turf growth prediction model only takes temperature into account, limiting its accuracy. This study developed machine-learning-based turf growth models using the random forest (RF) algorithm to estimate short-term turfgrass clipping yield. To build the RF model, a large set of variables were extracted as predictors including the 7-day weather, traffic intensity, soil moisture content, N fertilization rate, and the normalized difference red edge (NDRE) vegetation index. In this study, the data were collected from two putting greens where the turfgrass received 0 to 1,800 round/week traffic rates, various irrigation rates to maintain the soil moisture content between 9 and 29%, and N fertilization rates of 0 to 17.5 kg ha–1 applied biweekly. The RF model agreed with the actual clipping yield collected from the experimental results. The temperature and relative humidity were the most important weather factors. Including NDRE improved the prediction accuracy of the model. The highest coefficient of determination (R2) of the RF model was 0.64 for the training dataset and was 0.47 for the testing data set upon the evaluation of the model. This represented a large improvement over the existing growth prediction model (R2 = 0.01). However, the machine-learning models created were not able to accurately predict the clipping production at other locations. Individual golf courses can create customized growth prediction models using clipping volume to eliminate the deviation caused by temporal and spatial variability. Overall, this study demonstrated the feasibility of creating machine-learning-based yield prediction models that may be able to guide N fertilization decisions on golf course putting greens and presumably other turfgrass areas.

First Report of Summer Patch of Creeping Bentgrass Caused by Magnaporthiopsis poae in Southeastern China

Creeping bentgrass (Agrostis stolonifera L.) is an important cool-season perennial turfgrass that has been widely used on golf courses across China. In July 2017, an unknown disease outbreak caused damages on seven of the 18 putting greens of creeping bentgrass at Jiuqiao golf club in Hangzhou city of Zhejiang province, day-time high temperatures were consistently above 35°C during the disease development. Symptoms appeared in tan irregular patches of 5 to 20-cm diameter, exhibiting chlorosis and foliar dieback in most part. Necrotic roots were frequently observed in diseased areas and colonized with ectotrophic hyphae under a microscope. Similar symptoms and signs were reported on creeping bentgrass caused by Magnaporthiopsis poae (Landschoot & Jackson) J. Luo & N. Zhang on golf courses in Beijing (Hu et al. 2017). Fifteen disease samples were collected from seven putting greens. Dark root tips were cut, surface sterilized in 0.6% sodium hypochlorite (NaClO) for 5 min, washed twice with sterilized water, air dried for 1 min and placed on potato dextrose agar (PDA) containing each of 50 mg L-1 ampicillin, streptomycin sulfate, and tetracycline. Plates were incubated in the dark at room temperature for 4 days, and 10 fungal isolates with similar morphology as described by Clarke and Gould (1993) were consistently recovered from the diseased root tips. DNA of two representative isolates was extracted and amplified with primers ITS 5/ITS 4 (White et al. 1990). PCR products were sequenced (deposited in GenBank as MZ895215 and MZ895216), and BLAST analysis showed 99.17% similarity to M. poae (accession number: DQ528765). Six plastic pots (15 cm height × 15 cm top diameter × 10 cm bottom diameter, three replicates for each isolate) were seeded with creeping bentgrass and placed in the greenhouse for two months of plant growth before inoculation. The pathogenic inoculum was prepared by inoculating autoclaved oat seeds with M. poae isolates, followed by two weeks of incubation at 25°C. About 25 mg M. poae-infested oat seeds were placed 10 cm below the soil surface in the root zone of creeping bentgrass. Non-infested oat seeds were inoculated on healthy creeping bentgrass as controls. Pots were placed in a growth chamber with a 12-h day/night cycle at 35/28°C and watered daily to keep high soil moisture. Disease symptoms (foliar dieback and necrotic roots) were noted 3 weeks after inoculation. M. poae was consistently recovered from the roots of inoculated turf and identified molecularly as described above, fulfilling Koch’s postulates. To our knowledge, this is the first report of summer patch on creeping bentgrass caused by M. poae in southeastern China. This research demonstrates a wider distribution of M. poae and will be an important step towards the development of management strategies for summer patch control in China.

Characterization and aggressiveness of take-all root rot pathogens isolated from symptomatic bermudagrass putting greens

Take-all root rot is a disease of ultradwarf bermudagrass putting greens caused by Gaeumannomyces graminis (Gg), Gaeumannomyces sp. (Gx), Gaeumannomyces graminicola (Ggram), Candidacolonium cynodontis (Cc), and Magnaporthiopsis cynodontis (Mc). Many etiological and epidemiological components of this disease remain unknown. Improving pathogen identification and our understanding of the aggressiveness of these pathogens along with growth at different temperatures will advance our knowledge of disease development to optimize management strategies. Take-all root rot pathogens were isolated from symptomatic bermudagrass root and stolon pieces from 16 different golf courses. Isolates of Gg, Gx, Ggram, Cc, and Mc were used to inoculate ‘Champion’ bermudagrass in an in planta aggressiveness assay. Each pathogen was also evaluated at 10, 15, 20, 25, 30, and 35C to determine growth temperature optima. Infected plant tissue was used to develop a real-time PCR high resolution melt assay for pathogen detection. This assay was able to differentiate each pathogen directly from infected plant tissue using a single primer pair. In general, Ggram, Gg, and Gx were the most aggressive while Cc and Mc exhibited moderate aggressiveness. Pathogens were more aggressive when incubated at 30C compared to 20C. While they grew optimally between 24.4 and 27.8C, pathogens exhibited limited growth at 35C and no growth at 10C. These data provide important information on this disease and its causal agents that may improve take-all root rot management.

Investigating low-dose herbicide programs for goosegrass (Eleusine indica) and smooth crabgrass (Digitaria ischaemum) control on creeping bentgrass greens

Only four herbicides are registered for smooth crabgrass or goosegrass control on creeping bentgrass golf putting greens. None of the four herbicides control weedy grasses for the entire season or control weeds postemergence when applied once at labeled rates. Three of these have product labels that prohibit repeated use or application during stressful summer conditions. We hypothesized frequently applying herbicides at low doses could provide season-long control of summer grasses while minimizing turf injury. Seven field experiments were conducted on creeping bentgrass putting greens to evaluate various herbicides applied monthly, biweekly, or weekly for postemergence and residual control of goosegrass and smooth crabgrass as well as creeping bentgrass putting green tolerance. Metamifop applied twice monthly at 200 g ai ha−1, topramezone applied eight times weekly at 1.5 g ae ha−1, and siduron applied weekly at 5.6 kg ai ha−1 or four times biweekly at 11 kg ha−1 did not injure creeping bentgrass greater than 10% and maintained creeping bentgrass quality and cover equivalent to nontreated turf. Weekly or biweekly programs of fenoxaprop or quinclorac caused unacceptable injury and quality decline. Metamifop applied monthly and either fenoxaprop program controlled both smooth crabgrass and goosegrass 97 to 99% throughout the growing season. Programs containing either quinclorac or siduron controlled smooth crabgrass 99 to 100% but did not control goosegrass greater than 39%. All topramezone programs controlled smooth crabgrass 69 to 77% and goosegrass 93 to 98%. In additional studies, siduron applied five times biweekly did not injure creeping bentgrass putting greens and controlled smooth crabgrass greater than 90% at seasonal, cumulative rates between 17 and 65 kg ai ha−1. This method of frequent, low-dose herbicide treatment to control smooth crabgrass and goosegrass on golf putting greens is novel and could be legally implemented currently with siduron.

Dose responses of silvery-thread moss (Bryum argenteum) to carfentrazone-ethyl

Carfentrazone-ethyl is one of few herbicides labeled for control of silvery-thread moss (STM) in golf course putting greens, but common use rates are up to three times higher than for broadleaf weeds. Our objective was to determine the efficacy of a single postemergence application of carfentrazone-ethyl for STM control in greenhouse and field dose response studies. In the greenhouse, carfentrazone-ethyl was applied at 0, 14, 28, 56, 112, and 224 g ai ha−1 to pots containing established STM and creeping bentgrass. Percent gametophyte injury was visually estimated at 14, 28, 49, and 77 d after treatment (DAT). Shoot viability was determined by excising shoots from treated pots and plating them in petri dishes containing sand. The 28 and 49 DAT ED90 (dose required to cause 90% gametophyte injury) were 26.8 and 54.3 g ha−1, respectively; both of these doses are substantially lower than the label rates for long- and short-term control, respectively. All doses reduced the viability of transplanted shoots at 10 DAT compared to untreated STM; however, regrowth occurred in all petri dishes by 17 DAT. Field studies were initiated in Manhattan, Kansas and San Luis Obispo, California to corroborate greenhouse results. Averaged across locations, carfentrazone-ethyl applied at 56 and 112 g ha−1 caused 76% and 84% STM injury at 14 DAT, but quickly reduced to 45% and 48% STM injury by 28 DAT, respectively. In greenhouse and field studies, STM recovery did not occur until after 2 wk after treatment (WAT), which indicates the label-stipulated application interval of 2 wk is too short. Our research suggests 56 g ha−1 can provide similar burndown control of STM as compared to the highest label rate (112 g ha−1), and turfgrass managers should consider extending the reapplication interval to 3 or 4 wk when moss recovery is observed.