Estimating Surface Wetness on Plants

Magarey, Roger D.; Seem, Robert C.; Weiss, Albert; Gillespie, T. J.; Huber, Laurent

doi:10.2134/agronmonogr47.c10

Cited by 22 publications

(22 citation statements)

References 100 publications

(197 reference statements)

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“…2.4 | Climate measurements LWS data were only available for limited periods in the wet season of 2011 and 2012. The use of dielectric sensors as a proxy for actual leaf wetness is limited by several factors, including leaf surface traits to retain or repel water (Armstrong, Barthakur, & Norris, 1993;Sentelhas, Monteiro, & Gillespie, 2004) and the high level of spatial variation in wetness condition and duration throughout a complex canopy (Giesler, Horst, & Yuen, 1996;Magarey, Seem, Weiss, Gillespoe, & Huber, 2005). Therefore, we constrain our use of LWS data to generalized relationships between sap flux and leaf wetness.…”

Section: Transpiration Measurement and Upscalingmentioning

confidence: 99%

Upscaling transpiration in diverse forests: Insights from a tropical premontane site

et al. 2017

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Upscaling water use of individual trees to stands using sap flux techniques is a common method for partitioning site water balance, but few such studies have occurred in the tropics. Increasing interests in the role of tropical forests in global cycles have spurred upscaling studies in natural tropical forests, which present challenges from greater tree species and functional diversity, and potential factors that would reduce transpiration, such as frequent cloud cover and wet canopy conditions. In a premontane wet tropical forest in central Costa Rica, sap flow was measured in 15 trees stratified into 5 size classes based on tree diameters. None of the trees belonged to the same species, genus, or even family. We also accounted for potential radial variation in sap flux density. Data were scaled to estimate transpiration within a small 2.2‐ha watershed using stand surveys of sapwood area. Stand transpiration averaged only 1.4 ± 0.7 mm day−1 within this forested watershed due to persistent low radiation, evaporative demand, and frequent wet canopy conditions. Our systematic approach used tree size attributes to scale water use to the stand, given difficulties to quantify species differences in such a diverse ecosystem. Contrary to previous evidence on temperate trees, the large trees sampled did not exhibit flow reductions in deeper sapwood, which warrants further study. These results highlight some unique aspects of measuring transpiration in wet tropical forests that are important to consider for future studies in diverse stands.

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Section: Transpiration Measurement and Upscalingmentioning

confidence: 99%

Upscaling transpiration in diverse forests: Insights from a tropical premontane site

et al. 2017

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“…This threshold has been adjusted in a number of models used throughout Europe; i.e, the French model, Milsol, uses a threshold of 86% (Gaucher, personal communication) and the Danish Blight management uses a threshold of 88% (Hansen, personal communication). There are a number of reasons to opt for lower risk when deciding on which reported relative humidity threshold should be considered blight favorable, such as accuracy of measurements, distance between weather data source and the production area, topography of the area, physiological and phenological differences in crop haulm density and shaded areas of the production fields [49,97,98].…”

Section: Discussionmentioning

confidence: 99%

Evaluation of the ‘Irish Rules’: The Potato Late Blight Forecasting Model and Its Operational Use in the Republic of Ireland

et al. 2019

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Potato late blight caused by Phytophthora infestans is one of the most important plant diseases known, requiring high pesticide inputs to prevent disease occurrence. The disease development is highly dependent on weather conditions, and as such, several forecasting schemes have been developed worldwide which seek to reduce the inputs required to control the disease. The Irish Rules, developed in the 1950s and calibrated to accommodate the meteorological network, the characteristics of potato production and the P. infestans population at the time, is still operationally utilized by the national meteorological agency, Met Éireann. However, numerous changes in the composition and dynamics of the pathosystem and the risks of production/economic consequences associated with potato late blight outbreaks have occurred since the inception of the Irish Rules model. Additionally, model and decision thresholds appear to have been selected ad hoc and without a clear criteria. We developed a systematic methodology to evaluate the model using the empirical receiver operating curve (ROC) analysis and the response surface methodology for the interpretation of the results. The methodology, written in the R language, is provided as an open, accessible and reproducible platform to facilitate the ongoing seasonal re-evaluation of the Irish Rules and corresponding decision thresholds. Following this initial analysis, based on the available data, we recommend the reduction of the thresholds for relative humidity and an initial period duration from 90% and 12 h to 88% and 10 h, respectively. Contrary to recent reports, we found that the risk of blight epidemics remains low at temperatures below 12 °C. With the availability of more comprehensive outbreak data and with greater insight into the founder population to confirm our findings as robust, the temperature threshold in the model could potentially be increased from 10 °C to 12 °C, providing more opportunities for reductions of pesticide usage. We propose a dynamic operational decision threshold between four and 11 effective blight hours (EBH) set according to frequency of the disease outbreaks in the region of interest. Although the risk estimation according to the new model calibrations is higher, estimated chemical inputs, on average, are lower than the usual grower’s practice. Importantly, the research outlined here provides a robust and reproducible methodological approach to evaluate a semi-empirical plant disease forecasting model.

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“…Unpainted flat panel sensors were used to detect occurrence of wetness under the shade. Because unpainted sensors tended to detect less wetness duration when small water droplets were formed on the sensors [4] , a pair of wetness sensors was installed [5] , [6] . It was assumed that wetness occurred when wetness was detected by at least one sensor.…”

Section: Methodsmentioning

confidence: 99%

Assessment of microclimate conditions under artificial shades in a ginseng field

Lee

Kang

et al. 2016

Journal of Ginseng Research

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BackgroundKnowledge on microclimate conditions under artificial shades in a ginseng field would facilitate climate-aware management of ginseng production.MethodsWeather data were measured under the shade and outside the shade at two fields located in Gochang-gun and Jeongeup-si, Korea, in 2011 and 2012 seasons to assess temperature and humidity conditions under the shade. An empirical approach was developed and validated for the estimation of leaf wetness duration (LWD) using weather measurements outside the shade as inputs to the model.ResultsAir temperature and relative humidity were similar between under the shade and outside the shade. For example, temperature conditions favorable for ginseng growth, e.g., between 8°C and 27°C, occurred slightly less frequently in hours during night times under the shade (91%) than outside (92%). Humidity conditions favorable for development of a foliar disease, e.g., relative humidity > 70%, occurred slightly more frequently under the shade (84%) than outside (82%). Effectiveness of correction schemes to an empirical LWD model differed by rainfall conditions for the estimation of LWD under the shade using weather measurements outside the shade as inputs to the model. During dew eligible days, a correction scheme to an empirical LWD model was slightly effective (10%) in reducing estimation errors under the shade. However, another correction approach during rainfall eligible days reduced errors of LWD estimation by 17%.ConclusionWeather measurements outside the shade and LWD estimates derived from these measurements would be useful as inputs for decision support systems to predict ginseng growth and disease development.

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Estimating Surface Wetness on Plants

Cited by 22 publications

References 100 publications

Upscaling transpiration in diverse forests: Insights from a tropical premontane site

Upscaling transpiration in diverse forests: Insights from a tropical premontane site

Evaluation of the ‘Irish Rules’: The Potato Late Blight Forecasting Model and Its Operational Use in the Republic of Ireland

Assessment of microclimate conditions under artificial shades in a ginseng field

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