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Management of sugarcane orange rust, caused by Puccinia kuehnii , currently relies on fungicide applications in Florida. Field experiments were conducted in 2016 and 2017 in Belle Glade, FL to evaluate the efficacy and application timing of fungicides on progress of disease severity and sugarcane yields. Two treatment programs of three fungicide applications each were applied to sugarcane cultivar CL85-1040 susceptible to orange rust. Each program was also started at three different initiation dates separated by one month, and the first treatment was initiated when rust severity reached 5–10% on the top visible dewlap (TVD) leaf. Program A consisted of two consecutive applications of fluxapyroxad + pyraclostrobin followed by an application of metconazole. Program B consisted of three consecutive applications of fluxapyroxad + pyraclostrobin, fluxapyroxad, and pyraclostrobin. For each program, the three fungicide applications were separated by one month each and control plots remained unsprayed. Percent leaf area affected by rust was recorded every two weeks on TVD leaf and leaf +2 (leaf immediately below TVD leaf). Fungicide treatment programs initiated at the beginning of orange rust epidemics resulted in highest reduction of disease severity (41–45%) and highest yield increase (26–33%) as compared to untreated control plants. These results suggested that the application of fungicides initiated through early epidemic season are required for best management of sugarcane orange rust. • Two fungicide management programs were equally effective in controlling sugarcane orange rust in Florida. • Best disease control was achieved when fungicide programs were initiated during the early disease epidemic period. • Disease severity of the top visible dewlap leaf was correlated with reduction in stalk weight at harvest. [ABSTRACT FROM AUTHOR]

Abstract: Basil downy mildew, caused by Peronospora belbahrii Thines sp. nov., is a devastating foliar disease of fresh-cut basil first discovered in the U.S. in South Florida in 2007. Since then the pathogen has been found in over 20 U.S. states and has become a major threat to sweet basil production. In this study, acibenzolar-S-methyl (ASM, Actigard 50WG), DL-3-aminobutyric acid (BABA), isonicotinic acid (INA), salicylic acid (SA) and sodium salicylate (SS) were evaluated for their potential to control basil downy mildew in the greenhouse. Efficacy of these systemic acquired resistance (SAR) inducers varied in control of basil downy mildew depending on the rate, method and timing of application. Foliar sprays of ASM applied pre-, post- or pre- + post-inoculation at rates ranging from 25 to 400 mg l−1 significantly (P = 0.05) reduced disease severity compared to the non-treated control in all experiments. ASM sprayed at 50 mg l−1 three times on a weekly basis starting 3 and 7 days post- inoculation resulted in a 93.8 and 47.1% reduction in disease severity, respectively. Six weekly foliar sprays of BABA as pre- + post-inoculation at rates equal or higher than 125 mg l−1 significantly suppressed downy mildew compared to the non-treated control. Foliar treatments of ASM or BABA followed by one or two post-inoculation sprays of a mixture of potassium phosphite (Prophyt) and azoxystrobin (Quadris) significantly improved efficacy for disease control. Sporangia counted on ASM treated leaves were significantly lower than leaves sampled from the non-treated control. ASM and BABA at concentrations lower than 1.0 mM did not inhibit sporangial germination in vitro. The effect of INA, SA and SS on disease reduction was generally inconsistent and not significant compared to the non-treated control. [Copyright &y& Elsevier]

Abstract: River discharges are usually gauged at sites farther upstream than estuarine tidal reaches. As a result, global estimates of river water and nutrient fluxes to the ocean are likely underestimated as they often neglect groundwater discharge occurring in estuaries downstream of river gauging stations. We used radon and radium isotopes as tracers of groundwater discharge into the Sebastian River Estuary, a gaining stream in Florida, USA. We developed a spatially-distributed mass balance model that accounts for radon sources and sinks in waters above and below the estuarine pycnocline. Radium isotopes (224Ra, 223Ra, and 226Ra) were not enriched in groundwater relative to surface water and thus had limited usefulness as tracers at this specific site. The detection of fresh groundwater just beneath the sediment:water interface overlain by brackish bottom water implies that fresh groundwater dominates over saline groundwater in this salt wedge estuary. Lateral groundwater inputs from sandy banks into waters above the estuarine pycnocline were about 6-fold higher than inputs into waters below the pycnocline. Groundwater discharge rates into the surface layer of the estuary estimated from a radon mass balance ranged from 5 to 18m3/s (or 18 to 62cm/day if uniformly distributed throughout the entire estuary area). The fluxes into the bottom layer ranged from 0.8 to 1.1m3/s (or 2.8 to 3.9cm/day). These groundwater inputs augmented river discharges gauged upstream of the estuary tidal reaches by about 260% during the dry period and 135% during the wet period. As nutrient and other dissolved species are often highly enriched in groundwaters, groundwater probably controls surface water quality in this and other Florida estuaries. [ABSTRACT FROM AUTHOR]

Summary: Naturally occurring 222Rn (radon; t 1/2 =3.8days) is a good natural tracer of groundwater discharge because it is conservative and typically 2–3 orders of magnitude higher in groundwater than surface waters. In addition, new technology has allowed rapid and inexpensive field measurements of radon-in-water. Results from the C-25 Canal, a man-made canal in east-central Florida thought to be dominated by groundwater inflows, display how one can quickly assess a water body for locations of groundwater inputs. Although only the eastern portion of the canal was surveyed, use of a few assumptions together with some continuous radon measurements allowed reasonable estimates of the groundwater inflows to be made. Groundwater discharge estimates of 327,000m3/day and 331,000m3/day were measured for two stations based on determining the groundwater fraction of the total stream flow. This fraction in each case was calculated by correcting radon concentrations for decay over transit times determined from concentration differences between the apparent focal point of groundwater discharge (with a concentration of 520±80dpm/L) estimated to be ∼17.7km upstream from the downstream sample locations. During the same period, an average flow of 312,000±70,000m3/day was determined from time-series measurements of radon at a fixed downstream location. Coincident current meter readings and a measured cross-section area allowed an independent assessment of the total stream discharge of 336,000m3/day. The radon-derived estimates thus indicate that >90% of the total flow is groundwater derived, consistent with the known characteristics of this waterway. [Copyright &y& Elsevier]

Abstract: We report the results of an experiment in which we measured 222Rn (15,000 observations), CH4 (40,000 observations), and associated variables in seawater nearly continuously at a coastal site in the Gulf of Mexico for almost two years. Significant correlations between 222Rn and CH4 imply that they are derived from a common source, most likely groundwater. However, we were unable to explain the overall tracer variability as a single function of groundwater table height, temperature, tidal range, and wind speed, indicating multiple, overlapping controls on SGD dynamics at this site. Methane and radon concentrations may vary 2-fold in a given well in the subterranean estuary over tidal time scales, demonstrating the complexity of determining SGD endmember concentrations and suggesting that unaccounted for temporal changes in groundwater may explain some of the patterns observed in seawater. Surprisingly, the variability of 222Rn and CH4 in seawater over short (e.g., hourly) time scales was generally comparable to or even more pronounced than fluctuations over much longer (e.g., monthly) scales. While high tracer concentrations usually occurred during low tide and low tracer concentrations during high tide, this pattern was occasionally inverted or absent indicating that no single model can be used to describe the entire data set. We also describe a sequence of events in which SGD tracers were depleted in coastal waters during storms and regenerated afterwards. We found no increase in radon activities immediately after the largest storm (75 mm rainfall) perhaps because of the short residence times of groundwater in contrast to the ingrowth time of radon. Marine controls appeared to be the most important SGD drivers with only minor influence relating to the shallow and deep aquifers. This implies that seasonal investigations of SGD tracers in the coastal ocean may be masked by short-term variability. [Copyright &y& Elsevier]

Abstract: The contribution of submarine groundwater discharge (SGD) to oceanic metal budgets is only beginning to be explored. Here, we demonstrate that biogeochemical processes in a northern Florida subterranean estuary (STE) significantly alter U and Ba concentrations entering the coastal ocean via SGD. Tidal pumping controlled the distribution of dissolved metals in shallow beach groundwater. Hourly observations of intertidal groundwaters revealed high U and low Ba concentrations at high tide as a result of seawater infiltration into the coastal aquifer. During ebb tide, U decreased and Ba increased due to freshwater dilution and, more importantly, biogeochemical reactions that removed U and added Ba to solution. U removal was apparently a result of precipitation following the reduction of U(VI) to U(IV). A significant correlation between Ba and dissolved organic carbon (DOC) in shallow beach groundwaters implied a common source, likely the mineralization of marine particulate organic matter driven into the beach face by tidal pumping. In deeper groundwaters, where the labile organic matter had been depleted, Ba correlated with Mn. We estimate that net SGD fluxes were −163 and +1660μmolm−1 d−1 for U and Ba, respectively (or −1 and +8μmolm−2 d−1 if a 200-m wide seepage area is considered). Our results support the emerging concept that subterranean estuaries are natural biogeochemical reactors where metal concentrations are altered relative to conservative mixing between terrestrial and marine endmembers. These deviations from conservative mixing significantly influence SGD-derived trace metal fluxes. [Copyright &y& Elsevier]