Assessing the Feasibility of Using Sentinel-2 Imagery to Quantify the Impact of Heatwaves on Irrigated Vineyards

Heatwaves are common in many viticultural regions of Australia. We evaluated the potential of satellite-based remote sensing to detect the effects of high temperatures on grapevines in a South Australian vineyard over the 2016-2017 and 2017-2018 seasons. The study involved: (i) comparing the normalized difference vegetation index (NDVI) from medium- and high-resolution satellite images; (ii) determining correlations between environmental conditions and vegetation indices (Vis); and (iii) identifying VIs that best indicate heatwave effects. Pearson's correlation and Bland-Altman testing showed a significant agreement between the NDVI of high- and medium-resolution imagery (R = 0.74, estimated difference ??0.093). The band and the VI most sensitive to changes in environmental conditions were 705 nm and enhanced vegetation index (EVI), both of which correlated with relative humidity (R = 0.65 and R = 0.62, respectively). Conversely, SWIR (short wave infrared, 1610 nm) exhibited a negative correlation with growing degree days (R = -0.64). The analysis of heat stress showed that green and red edge bands-the chlorophyll absorption ratio index (CARI) and transformed chlorophyll absorption ratio index (TCARI)-were negatively correlated with thermal environmental parameters such as air and soil temperature and growing degree days (GDDs). The red and red edge bands-the soil-adjusted vegetation index (SAVI) and CARI2-were correlated with relative humidity. To the best of our knowledge, this is the first study demonstrating the effectiveness of using medium-resolution imagery for the detection of heat stress on grapevines in irrigated vineyards.</p

Physiological Responses Of Grapevine Shoots To Water Stress And The Development Of A Microtensiometer To Continuously Measure Water Potential

Water availability plays a key role in growth processes in grapevines (Vitis vinifera L.), moderating the balance between vegetative and reproductive growth. It was hypothesized that differences in vegetative growth of individual shoots within a grapevine on a single cane were due to differences in the water status of those shoots as indicated by their midday stem water potentials, [PSI]md. A combination of leaf pressure chamber, leaf gas exchange, ultrasonic acoustic emissions, stem hydraulic measurements, and histology techniques were used on field-grown 'Riesling' grapevines that were subjected to progressive soil moisture deficits during the 2011 and 2012 growing seasons. Differences in [PSI]md were not large enough to explain the large differences in shoot length within a single vine. Longer shoots had greater hydraulic conductivities, but shorter shoots were found to have higher rates of xylem acoustic emissions occurring under less water stress (higher [PSI]md) than longer shoots. Longer shoots had larger cross-sectional xylem vessel area and somewhat less inter-vessel pitting compared to shorter shoots. These differences could contribute to the higher hydraulic efficiency of long shoots, and with fewer pits per vessel, there may be fewer embolisms. Stomatal conductance and photosynthetic responses to increasing water stress were not different in relation to shoot length. In summary, although there were differences in water status between long and short shoots on the same vine, the differences were not great enough to explain the differences in growth rate of the shoots. Tensiometry is a technique to measure the chemical potential of stretched liquid water based on a thermodynamic equilibrium between liquid water and its vapor. It provides the most sensitivity in the range of (high) water potentials relevant to plants and soils, and is compatible with miniaturization for embedding in plants. Based on this technique, we developed a i microelectromechanical system (MEMS)-based microtensiometer in which a piezoresistive pressure sensor coupled to a nanoporous silicon membrane was able to measure large internal negative pressures of liquid when exposed to sub-saturated vapors. We demonstrated its function in sub-saturated vapors across a range of activities (aw) or relative humidities (RH), measuring internal hydrostatic pressures approaching -33 MPa (aw=0.78 or 78% RH), the largest negative liquid pressure directly measured by any method. The extended range of measurement combined with a small form factor make the microtensiometer an attractive instrument for the measurement of water activity in a variety of materials (e.g. concrete), physical, biological, and environmental systems. The microtensiometer can also be embedded in the stems of woody plants and in soils for the continuous measurement of water potential. Scalable microtensiometer arrays in conjunction with wireless networks offer the potential to provide continuous, high-resolution data to geographic information system (GIS) centers to aid in irrigation decisions and optimize water resource management for sustainable crop production. i

Evaluating Remotely-Sensed Grapevine (Vitis vinifera L.) Water Stress Responses Across a Viticultural Region

The evolving spatial and temporal knowledge about vineyard performance through the use of remote sensing offers new perspectives for vine water status studies. This paper describes the application of aerial thermal imaging to evaluate vine water status to improve irrigation scheduling decisions, water use efficiency, and overall winegrape quality in the Coonawarra viticultural region of South Australia. Airborne infrared images were acquired during the 2016 and 2017 growing seasons in the region of Coonawarra, South Australia. Several thermal indices of crop water status (CWSI, Ig, (Tc-Ta)) were calculated that correlated with conventional soil and vine water status measures (&Psi;pd, &Psi;s, gs). CWSI and Ig could discriminate between the two cultivars used in this study, Cabernet Sauvignon (CAS) and Shiraz (SHI), as did the conventional water stress measures. The relationship between conventional vine water status measures appeared stronger with CWSI in the warmer and drier season (2016) compared to the cooler and wetter season (2017), where Ig and (Tc-Ta) showed stronger correlations. The study identified CWSI, Ig and (Tc-Ta) to be reliable indicators of vine water status under a variety of environmental conditions. This is the first study to report on high resolution vine water status at a regional scale in Australia using a combination of remote and direct sensing methods. This methodology is promising for aerial surveillance of vine water status across multiple blocks and cultivars to inform irrigation scheduling

Effects of timing and intensity of elevated temperatures on reproductive development of field-grown Shiraz grapevines

Aim: To investigate whether timing and duration of exposure to elevated temperatures impact the reproductive development of field-grown Shiraz grapevines. Methods and results: The reproductive responses of Shiraz grapevines (Vitis vinifera L.) to two levels of elevated temperatures at budburst and flowering were investigated in an irrigated vineyard in the Barossa Valley (South Australia) over two consecutive growing seasons. Custom-built under-vine ‘tents’ and closed flow-through chambers enclosing a set of grapevines in the field were used to raise canopy temperatures above ambient. Higher temperatures at flowering resulted in lower yields due to decreased fruit set in 2007-08, while yield was virtually unaltered the following year despite the lower fruit set. Two indicators of grapevine reproductive performance, Coulure Index and Millerandage Index that quantify abscised and underdeveloped berries, respectively, were calculated to be higher as a result of the heat treatments in both seasons. Stigma receptivity, pollen germination, and pollen tube kinetics were generally lower in vines grown under the tents. Conclusion: Flowering and fruit set are strongly influenced by temperature changes during this period of development. Significance and impact of study: This is one of the first field based studies to demonstrate that extreme temperatures (>35°C) during the flowering period detrimentally effect fruit set and final yield and thus providing critical knowledge for managing vineyards in a changing climate

Estimation of Grapevine Crop Coefficient Using a Multispectral Camera on an Unmanned Aerial Vehicle

Crop water status and irrigation requirements are of great importance to the horticultural industry due to changing climatic conditions leading to high evaporative demands, drought and water scarcity in semi-arid and arid regions worldwide. Irrigation scheduling strategies based on evapotranspiration (ET), such as regulated deficit irrigation, requires the estimation of seasonal crop coefficients (kc). The ET-driven irrigation decisions for grapevines rely on the sampling of several kc values from each irrigation zone. Here, we present an unmanned aerial vehicle (UAV)-based technique to estimate kc at the single vine level in order to capture the spatial variability of water requirements in a commercial vineyard located in South Australia. A UAV carrying a multispectral sensor is used to extract the spectral, as well as the structural, information of Cabernet Sauvignon grapevines. The spectral and structural information, acquired at the various phenological stages of the vine through two seasons, is used to model kc using univariate (simple linear), multivariate (generalised linear and additive) and machine learning (convolution neural network and random forest) model frameworks. The structural information (e.g., canopy top view area) had the strongest correlation with kc throughout the season (p ≤ 0.001; Pearson R = 0.56), while the spectral indices (e.g., normalised indices) turned less-sensitive post véraison—the onset of ripening in grapes. Combining structural and spectral information improved the model’s performance. Among the investigated predictive models, the random forest predicted kc with the highest accuracy (R2: 0.675, root mean square error: 0.062, and mean absolute error: 0.047). This UAV-based approach improves the precision of irrigation by capturing the spatial variability of kc within a vineyard. Combined with an energy balance model, the water needs of a vineyard can be computed on a weekly or sub-weekly basis for precision irrigation. The UAV-based characterisation of kc can further enhance the water management and irrigation zoning by matching the infrastructure with the spatial variability of the irrigation demand

Evaluating the Potential of High-Resolution Visible Remote Sensing to Detect Shiraz Disease in Grapevines

Background and Aims. Shiraz disease (SD) is a viral disease associated with Grapevine virus A that causes significant yield loss in economically important grape cultivars in Australia such as Shiraz and Merlot. Current diagnostic methods are time-consuming and costly. This study evaluates an alternative methodology using visible remote sensing imagery to detect SD in Shiraz grapevines. Methods and Results. High-resolution visible remote sensing images were captured of Shiraz grapevines in two South Australian viticultural regions over two seasons. The projected leaf area (PLA) of individual grapevines was estimated from the images. Virus-infected vines had significantly lower PLA than healthy vines in the early season but fewer difference after veraison. The lower PLA was only observed in grapevines coinfected with grapevine leafroll-associated viruses (GLRaVs) and Grapevine virus A (GVA). Shiraz vines infected with either GLRaVs or GVA had similar PLA to healthy vines. Conclusions. High-resolution RGB remote sensing technology has the potential to rapidly estimate SD infection in Shiraz grapevines. Our observations of shoot devigouration only in coinfected vines calls into question the etiology of SD. Further validation of the PLA technique incorporating different regions, seasons, cultivars, and combinations of viruses is needed for improving the robustness of the method. Significance of the Study. This preliminary study presents a new rapid and low-cost surveillance method to estimate SD infections in Shiraz vineyards, which could significantly lower the cost for growers who conduct on-ground SD visual assessments or lab-based tissue testing at the vineyard scale

The influence of bird netting on yield and fruit, juice, and wine composition of <em>Vitis vinifera</em> L.

Aims: To investigate the impact of semi-permanent bird netting and timing of its application on Cabernet franc grapevine yield components and fruit, juice, and wine composition. Methods and results: Semi-permanent bird netting was installed over Cabernet franc grapevines at various times – post-bloom, bunch closure, and veraison – of the 2004 growing season in the Niagara Peninsula of Canada. At harvest, vine yield components were measured followed by berry and must compositional analysis of soluble solids, pH, titratable acidity (TA), color, and polyphenols. Wines made from these grapes were also analyzed (pH, TA, color, and polyphenols). It was found that installation of bird netting over grapevines had minimal effect on yield components and berry composition regardless of when the nets were installed. Must composition revealed significant decreases in soluble solids, pH, and color as a result of the netting, the least impact being when the nets were applied at post-bloom. Wine composition was similar to the must data with the netted treatments resulting in lower pH, higher TA, and decreased color. Total anthocyanins and polyphenols were slightly reduced as a result of the netting. Conclusions: Minimal impact of bird netting on yield, fruit, must and wine quality is a positive finding since netting is becoming more prevalent in vineyards worldwide due to changing migratory patterns of birds. It is recommended that netting be applied around post-bloom for the ease of application, to minimize shading effects, which could lead to decreased fruit quality, and to maintain yield. Significance and impact of the study: Use of bird netting is becoming more prevalent by grape growers worldwide due to changing migratory patterns of birds that feed on grapes. This study shows that bird netting is not detrimental to yield and fruit and wine quality especially when applied early in the growing season

Plant Viral Disease Detection: From Molecular Diagnosis to Optical Sensing Technology&mdash;A Multidisciplinary Review

Plant viral diseases result in productivity and economic losses to agriculture, necessitating accurate detection for effective control. Lab-based molecular testing is the gold standard for providing reliable and accurate diagnostics; however, these tests are expensive, time-consuming, and labour-intensive, especially at the field-scale with a large number of samples. Recent advances in optical remote sensing offer tremendous potential for non-destructive diagnostics of plant viral diseases at large spatial scales. This review provides an overview of traditional diagnostic methods followed by a comprehensive description of optical sensing technology, including camera systems, platforms, and spectral data analysis to detect plant viral diseases. The paper is organized along six multidisciplinary sections: (1) Impact of plant viral disease on plant physiology and consequent phenotypic changes, (2) direct diagnostic methods, (3) traditional indirect detection methods, (4) optical sensing technologies, (5) data processing techniques and modelling for disease detection, and (6) comparison of the costs. Finally, the current challenges and novel ideas of optical sensing for detecting plant viruses are discussed

Plant Viral Disease Detection: From Molecular Diagnosis to Optical Sensing Technology—A Multidisciplinary Review

Plant viral diseases result in productivity and economic losses to agriculture, necessitating accurate detection for effective control. Lab-based molecular testing is the gold standard for providing reliable and accurate diagnostics; however, these tests are expensive, time-consuming, and labour-intensive, especially at the field-scale with a large number of samples. Recent advances in optical remote sensing offer tremendous potential for non-destructive diagnostics of plant viral diseases at large spatial scales. This review provides an overview of traditional diagnostic methods followed by a comprehensive description of optical sensing technology, including camera systems, platforms, and spectral data analysis to detect plant viral diseases. The paper is organized along six multidisciplinary sections: (1) Impact of plant viral disease on plant physiology and consequent phenotypic changes, (2) direct diagnostic methods, (3) traditional indirect detection methods, (4) optical sensing technologies, (5) data processing techniques and modelling for disease detection, and (6) comparison of the costs. Finally, the current challenges and novel ideas of optical sensing for detecting plant viruses are discussed