Drones: Innovative Technology for Use in Precision Pest Management.

Arthropod pest outbreaks are unpredictable and not uniformly distributed within fields. Early outbreak detection and treatment application are inherent to effective pest management, allowing management decisions to be implemented before pests are well-established and crop losses accrue. Pest monitoring is time-consuming and may be hampered by lack of reliable or cost-effective sampling techniques. Thus, we argue that an important research challenge associated with enhanced sustainability of pest management in modern agriculture is developing and promoting improved crop monitoring procedures. Biotic stress, such as herbivory by arthropod pests, elicits physiological defense responses in plants, leading to changes in leaf reflectance. Advanced imaging technologies can detect such changes, and can, therefore, be used as noninvasive crop monitoring methods. Furthermore, novel methods of treatment precision application are required. Both sensing and actuation technologies can be mounted on equipment moving through fields (e.g., irrigation equipment), on (un)manned driving vehicles, and on small drones. In this review, we focus specifically on use of small unmanned aerial robots, or small drones, in agricultural systems. Acquired and processed canopy reflectance data obtained with sensing drones could potentially be transmitted as a digital map to guide a second type of drone, actuation drones, to deliver solutions to the identified pest hotspots, such as precision releases of natural enemies and/or precision-sprays of pesticides. We emphasize how sustainable pest management in 21st-century agriculture will depend heavily on novel technologies, and how this trend will lead to a growing need for multi-disciplinary research collaborations between agronomists, ecologists, software programmers, and engineers

Summaries of Arkansas Cotton Research in Progress in 2001

Cotton yields in Arkansas increased steadily during the eighties, but in recent years there has been a leveling off. Of more significance, however, is that extreme year-to-year variability in yields has occurred in the last decade, which is a major point of concern with cotton producers. It has been suggested that this may be related to extreme weather conditions during the boll development period in July and August. Average maximum temperatures in the 2001 season were a few degrees above normal. Recent research in Arkansas has indicated that elevated night temperatures during boll development may be a major contributory factor to low and variable yields. There is also evidence that yield variability in stressful seasons may be related to genotypic changes in the components of yield, seed number, and fiber per seed, over the last 30 years. Yield stability for Arkansas cotton producers has become a major focus for new in-state collaborative research projects

The Detection of Potato Cyst Nematode (PCN) Infestation Using Remotely Sensed Imagery

Potato cyst nematodes (PCN) Globodera pallida Stone and G. rostochiensis (Wollenweber) are economically-important pests which cause significant losses to potato production world-wide. Population control is a major objective of a sustainable management strategy as nematodes are persistent and reproductive rates can be high. Current methods of determining PCN population densities are both expensive and time consuming: an advance on current sampling methods would facilitate the application of precision farming methods to PCN management. The potential for using light reflected from the potato canopy as an assay to detect PCN infestation is investigated. Spectral reflectance was measured from the canopy of commercial potato crops, individual plants and single leaves with a field spectrometer, airborne remote sensing and from SPOT and Ikonos satellite images. Comparisons between the reflectance from healthy and infected plants revealed a significant reduction in green (c. 550nm) reflectance from infested plants, and this was consistent across seasons, cultivars and imaging methods. The strongest results were seen early in the crop cycle, although full canopy development is desirable in airborne and satellite image analysis. Yield-limiting pathogens are frequently reported as increasing visible reflectance by reducing chlorophyll concentration in the leaves of afflicted plants. The spectral response to PCN infestation is distinct from that from common plant stress factors and a PCN- specifrc detector system is proposed. A viable commercial PCN assay would need to be timely, reliable and cost-effective. Whilst aircraft and satellite platforms offer the rapid acquisition of data from large areas, these imaging methods are heavily dependent on weather conditions. Results from data collected using a hand-held chlorophyll meter in this investigation indicate that a closed, or semi-closed imaging system (enclosing or covering the plant canopy) would be suited to the detection of PCN under field conditions and less susceptible to inclement weather

TEMPERATURE-TIME THRESHOLDS FOR IRRIGATION SCHEDULING IN DRIP AND DEFICIT FURROW IRRIGATED COTTON

Water is one of the most limiting factors to Australian cotton production. Improved irrigation scheduling efficient water use is central to the sustainability of the Australian irrigated cotton industry. Irrigation scheduling is a two-fold process where-by the amount and frequency of water applied to a plant is determined. Producers must aim to optimise crop water use through timely irrigation scheduling and efficient utilisation of in-crop rainfall. Currently, furrow irrigation is the dominant form of irrigation delivery and cotton farmers use a limited range of methods to make irrigation decisions. A combination of the cost, accuracy and complexity of these methods has limited their effective use in commercial production. In this study a potentially simpler method based on crop canopy temperatures and the thermal optimum concept was investigated. Compared to well-watered plants, water stressed plants exhibit elevated canopy temperatures. This is a consequence of the closing of stomata, in response to soil water deficits. The closure of stomata results in a decrease in transpiration and consequently a reduction in latent energy flux, leading to a rise in canopy temperatures. However, ambient conditions can have a large influence on canopy temperatures; thus canopy temperatures are a reflection of both plant and environmental factors. In order to develop indicators of the early onset of water and temperature stress, research conducted in the USA developed a theory that defined optimal plant temperatures with respect to the thermal dependence of the Michaelis-Menten constant of an enzyme (Km). The optimal enzymatic function was restricted to a range of ambient temperatures that was termed the thermal kinetic window (TKW), which is an indicator of the optimal temperature range of a plant species. Using alternative diagnostic methodologies of chlorophyll fluorescence recovery rates and analysis of plant physiological function under field conditions, the optimal temperature of an Australian cultivar was identified to be ~28 °C. Although this was consistent with values obtained from US cotton cultivars, and average day-time canopy temperatures that were achieved in the field at close to optimal water applications, it was important to verify this as Australian cotton cultivars are genetically different to US cultivars and the combined effect of different genetics and ecological adaptations may potentially influence the optimal temperature of biochemistry. The TKW theory was used as the basis for the BIOTIC (Biologically Identified Optimal Temperature Interactive Console) protocol. This protocol was developed by researchers at the USDA-ARS, and uses the relationship between canopy temperature (Tc) and plant water status to schedule irrigation using a temperature-time threshold system. Irrigations are commanded when the crop’s Tc exceeds an optimal temperature threshold for a pre-determined period of time. Using the BIOTIC system as a basis, this study aims to assess the physiological base and utility of the thermal optimal approach to schedule irrigation, with particular emphasis on its use in precision application and large soil water deficit irrigation systems of the Australian cotton industry. Deficit irrigation is an optimisation strategy where full crop water requirements are not necessarily provided, improving water-use efficiency (WUE). The thermal optimal approach was studied previously; however, its use was limited to irrigation systems that provide full water requirements at high irrigation frequencies and low irrigation volumes. Hence, its application to deficit and furrow irrigation systems was unknown. The physiological basis of the principles underlying the thermal optimum concept for irrigation scheduling was examined through the monitoring of Tc of the commercial cotton cultivar Sicot 70BRF at ‘Myall Vale’ Narrabri Australia. Surface drip irrigation experiments were conducted in the 2007/08 and 2008/09 seasons, where irrigation treatments were based on daily crop evapotranspiration (ETC) rates calculated using the FAO56 protocol with a locally calibrated crop coefficient. A furrow-irrigated experiment was conducted in the 2008/09 season, where irrigation treatments were based on plant available soil water deficits (mm) from field capacity calculated from neutron attenuation data. The objectives of this research were to: (1) confirm that the optimum temperature (Topt) of a current commercial Australian cotton cultivar (Sicot 70BRF) is the same as other measured USA cotton cultivars; (2) determine if Tc can define plant water stress by comparison with soil and atmospheric conditions; and (3) determine the potential of the thermal optimum approach to scheduling irrigation in Australian cotton systems. The hypothesis that Tc provides sufficient information for irrigation scheduling was investigated in the surface drip and furrow irrigated cotton. Irrigation treatments resulted in differences in lint yield, plant architecture, growth, biomass accumulation and Tc. Canopy temperatures were correlated with crop lint yield and the volume of water applied to the crop. Peak lint yields occurred at average day-time (Rn > 300 W m-2) Tc of 26.4 ± 1.7 °C and total water of 108% calculated ETC under surface drip conditions, and at Tc of 28.6 °C ± 0.6 °C and water supplies of 99% calculated ETC under furrow irrigated conditions. Acclimation of Tc due to the wetting and drying cycles of furrow irrigation did not occur and the combination of both furrow and drip irrigated data showed a single relationship where peak lint yields occurred at Tc of 28 °C. This highlights the benefits of maintaining average canopy temperatures close to 28 °C, and supports the potential utility of the thermal optimum concept in Australian drip and furrow irrigated cotton. Although lint yield is proportional to the thermal optimum, the physiological limitations of a plant can mean that a well-watered plant’s Tc can still exceed the thermal optimum. This gives rise to the stress time (ST) concept, where ST represents the average daily period of time that a well-watered crop’s Tc can exceed its optimum temperature. The ST concept was tested and adapted to Australian field-based drip and furrow irrigation systems. Peak lint yields and crop WUE (the ratio of lint yield produced per hectare to the cumulative amount of water used by the crop through evapotranspiration) in drip-irrigated cotton occurred at 4.5 h ST, considerably higher than the empirically calculated threshold of 2.8 h. A thermal optimum protocol was developed to schedule furrow irrigation events through a cumulative ST approach, where one ST h represents 0.6 mm plant available soil water depletion, enabling a producer to determine the desired soil water deficit and schedule irrigations based on cumulative ST. An integrated approach to stress detection was also proposed. This approach, the sum of cumulative ST, is theoretically advantageous as it considers both the degree and duration of time Tc exceeding the optimum. The physiological principle underlying a thermal optimal approach to irrigation scheduling were analysed in this thesis. An independently estimated optimal temperature was determined to be 28 °C. This optimal temperature was correlated with peak lint yields, and Tc was responsive to irrigation. A stress time threshold producing peak lint yield was developed in surface drip irrigation systems, and a cumulative stress time threshold for soil water deficits was outlined for furrow irrigation systems. These modified stress time thresholds provided the information required to detect water stress for irrigation scheduling. The practical implication of this research is that temperature-time thresholds in a thermal optimal irrigation scheduling system have utility in the irrigated Australian cotton industry. However, the time thresholds that were determined in this study were developed by monitoring cotton crops with infra red thermometers, and irrigations were not scheduled with a thermal optimum protocol in this study. With field validation, these irrigation protocols could be used as the basis for a modified BIOTIC system and be adopted by the commercial cotton industry, as it is a simple, cost effective irrigation scheduling system

Evaluation of Late Season Potassium Applications to Arkansas Soybean

Potassium (K) deficiency is one of the most important yield limiting factors in Arkansas soybean (Glycine max (L.) Merr.) production, although there are recently improved diagnostic and management opportunities available. However, several questions regarding the successful implementation of in-season K management in soybean production remain. Therefore, the research objectives were to (a) delineate the relationship between drought stress and K deficiency on soybean vigor, (b) identify the spatial dependencies of leaf-K concentrations at the production scale, (c) develop a leaf sampling protocol, (d) calibrate the fertilizer-K rate needed to correct varying levels of K deficiency at 15, 30, and 45 days after first flower (DAR1), and (e) evaluate the economics of in-season K management in soybean. The research encompassed complementary rain-out shelter and field experiments at the small plot scale as well as commercial production fields. Drought stress significantly (P \u3c 0.05) reduced the total K uptake (TKU), aboveground biomass production, and yield, with greater reductions when drought stress was imposed during reproductive growth. Across producer managed fields, no consistent spatial dependencies were found in the leaf-K concentrations indicating that a soybean tissue-K grid sampling protocol cannot be generalized to a specific area size. Therefore, one composite sample consisting of at least 18 of the upper-most fully expanded trifoliolate leaves from each management zone is appropriate to capture the area’s crop nutritional K status. Additional small plot research was conducted on silt loam soils to quantify the level of deficiency with trifoliolate leaf samples and assess the yield response to corrective applications of 0 to 149 kg K ha-1 at 15, 30 and 45 DAR1. As expected, higher levels of deficiency required higher rates of fertilization to reach the yield goal. Linear plateau models were considered for each timing, using the join point as the threshold determining whether a corrective application is warranted. The parameters of the significant (P \u3c 0.05) individual models predicting the 15 and 30 DAR1 rate recommendations were not statistically different (P = 0.902). Therefore, data were combined and a new model fit, providing a predicted site-specific fertilizer-K rate recommendation from R2 to 30 DAR1. At both the 15 and 30 DAR1 times, economic ramifications associated with corrective applications were quantified in a payoff matrix by calculating yield averages, partial returns (PR), and regret, each assuming 5-year average prices. At both times, large increases in PR and differences in regret were reported when in-season K deficiencies occurred. The 45 DAR1 results failed to provide a reasonable calibration curve (P = 0.401), suggesting that this is too late to correct a K deficiency in soybean. Overall, the ability to follow a leaf sampling protocol to appropriately capture a soybean field’s K status and use the results to determine a site-specific, calibrated fertilizer-K rate will enable producers to diagnose and correct deficiencies in-season and maximize both yield and profit. These research findings are the first to provide site-specific fertilizer-K rate recommendations for in-season applications and accompany the information with economic payoff matrices to facilitate informed management decisions

UVR8 mediated spatial differences as a prerequisite for UV-B induced inflorescence phototropism

In Arabidopsis hypocotyls, phototropins are the dominant photoreceptors for the positive phototropism response towards unilateral ultraviolet-B (UV-B) radiation. We report a stark contrast of response mechanism with inflorescence stems with a central role for UV RESISTANCE LOCUS 8 (UVR8). The perception of UV-B occurs mainly in the epidermis and cortex with a lesser contribution of the endodermis. Unilateral UV-B exposure does not lead to a spatial difference in UVR8 protein levels but does cause differential UVR8 signal throughout the stem with at the irradiated side 1) increase of the transcription factor ELONGATED HYPOCOTYL 5 (HY5), 2) an associated strong activation of flavonoid biosynthesis genes and flavonoid accumulation, 3) increased GA2oxidase expression, diminished gibberellin1 levels and accumulation of DELLA protein REPRESSOR OF GA1 (RGA) and, 4) increased expression of the auxin transport regulator, PINOID, contributing to local diminished auxin signalling. Our molecular findings are in support of the Blaauw theory (1919), suggesting that differential growth occurs trough unilateral photomorphogenic growth inhibition. Together the data indicate phototropin independent inflorescence phototropism through multiple locally UVR8-regulated hormone pathways

Determination of Time Dependent Stress Distribution on Potato Tubers at Mechanical Collision

This study focuses on determining internal stress progression and the realistic representation of time dependent deformation behaviour of potato tubers under a sample mechanical collision case. A reverse engineering approach, physical material tests and finite element method (FEM)-based explicit dynamics simulations were utilised to investigate the collision based deformation characteristics of the potato tubers. Useful numerical data and deformation visuals were obtained from the simulation results. The numerical results are presented in a format that can be used for the determination of bruise susceptibility magnitude on solid-like agricultural products. The modulus of elasticity was calculated from experimental data as 3.12 [MPa] and simulation results showed that the maximum equivalent stress was 1.40 [MPa] and 3.13 [MPa] on the impacting and impacted tubers respectively. These stress values indicate that bruising is likely on the tubers. This study contributes to further research on the usage of numerical-methods-based nonlinear explicit dynamics simulation techniques in complicated deformation and bruising investigations and industrial applications related to solid-like agricultural products

Tree Peony Species Are a Novel Resource for Production of α-Linolenic Acid

Tree peony is known worldwide for its excellent ornamental and medical values, but recent reports that their seeds contain over 40% α-linolenic acid (ALA), an essential fatty acid for humans drew additional interest of biochemists. To understand the key factors that contribute to this rich accumulation of ALA, we carried out a comprehensive study of oil accumulation in developing seeds of nine wild tree peony species. The fatty acid content and composition was highly variable among the nine species; however, we selected a high- (P. rockii) and low-oil (P. lutea) accumulating species for a comparative transcriptome analysis. Similar to other oilseed transcriptomic studies, upregulation of select genes involved in plastidial fatty acid synthesis, and acyl editing, desaturation and triacylglycerol assembly in the endoplasmic reticulum was noted in seeds of P. rockii relative to P. lutea. Also, in association with the ALA content, transcript levels for fatty acid desaturases (SAD, FAD2 and FAD3), which encode for enzymes necessary for polyunsaturated fatty acid synthesis were higher in P. rockii compared to P. lutea. We further showed that the overexpression of PrFAD2 and PrFAD3 in Arabidopsis increased linoleic and α-linolenic acid content, respectively and modulated their final ratio in the seed oil. In conclusion, we identified the key steps that contribute to efficient ALA synthesis and validated the necessary desaturases in P. rockii that are responsible for not only increasing oil content but also modulating 18:2/18:3 ratio in seeds. Together, these results will aid to improve essential fatty acid content in seeds of tree peonies and other crops of agronomic interest