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- Author or Editor: Wesley Wright x
Nursery producers are challenged with growing a wide range of species with little to no detectable damage from insects or diseases. Growing plants that meet consumer demand for aesthetics has traditionally meant routine pesticide application using the most time-efficient method possible, an air-blast sprayer, despite its known poor pesticide application efficiency. New variable-rate spray technology allows growers to make more targeted applications and reduce off-target pesticide loss. In this study, a prototype laser-guided variable-rate sprayer was compared with a traditional air-blast sprayer. Pesticide volume, spray application characteristics, and the control of powdery mildew were evaluated over the course of two growing seasons. Spray application characteristics were assessed using water-sensitive cards (WSCs) and DepositScan software. This prototype sprayer reduced pesticide volume by an average of 54% across both years despite being tested against a low rate (<250 L⋅ha−1). In 2016, the conventional sprayer had more than double the deposit density on target WSCs among distal trees than the variable-rate sprayer; however, within proximal trees, there was no difference between the two sprayer types. In 2017, when the trees were larger, within both the distal and proximal trees, the conventional sprayer had greater deposit density on target WSCs than the variable-rate sprayer. In 2016, coverage on target WSCs was nearly 7-fold greater with the conventional treatment than with the variable-rate treatment. In 2017, when trees were larger, there was greater coverage on target WSCs in proximal trees (3.8%) compared with those in distal trees (1.0%) regardless of the sprayer type. This variable-rate spray technology provided acceptable control of powdery mildew severity on individual branches and whole trees and maintained the incidence of powdery mildew to levels comparable to that occurring among trees sprayed with a traditional air-blast sprayer. Therefore, the variable-rate spray technology has the potential to effectively control disease, dramatically reduce the pesticide footprint, and preserve natural resources such as ground and surface water, soil, and beneficial insects found within and around nurseries.
Advanced variable-rate spray technology, which applies pesticides based on real-time scanning laser rangefinder measurements of plant presence, size, and density, was developed and retrofitted to existing sprayers. Experiments were conducted to characterize the application of four programmed spray rates (0.03, 0.05, 0.07, or 0.09 L·m−3 of crop geometric volume) when applied to Malus domestica Borkh. ‘Golden Delicious’ apple trees using this crop sensing technology. Water-sensitive cards (WSCs) were used as samplers to quantify spray coverage, deposits, and deposit density in the target and nontarget areas, and an overspray index based on a threshold of greater than 30% coverage was calculated. The application rate ranged from 262 L·ha−1 at the programmed spray rate of 0.03 L·m−3 to 638 L·ha−1 at the rate of 0.09 L·m−3. For a given WSC position, spray coverage and deposits increased as the spray rate increased. WSC positions 1 and 2 were oversprayed at all rates. The effect of spray rate on deposit density varied with WSC positions, with high densities achieved by low spray rates for WSCs closest to the sprayer but by high spray rates for WSCs positioned either deeper within or under the canopy. When coalescing deposits were accounted for, deposit densities met or exceeded the recommended pesticide application thresholds (insecticides 20–30 droplets/cm2; fungicides 50–70 droplets/cm2) at all WSC positions for each spray rate tested. The lowest spray rate reduced off-target loss to the orchard floor by 81% compared with the highest rate, dramatically reducing potential exposure to nontarget organisms, such as foraging pollinators, to come into contact with pesticide residues. Applying the lowest rate of 0.03 L·m−3 met deposit density efficacy levels while reducing spray volume by 83% compared with the orchard standard application of 1540 L·ha−1 and by 87% compared with the 1950 L·ha−1 application rate recommended when using the tree row volume method. Thus, there is potential for growers to refine pesticide application rates to further achieve significant pesticide cost savings. Producers of other woody crops, such as nursery, citrus, and grapes, who use air-assisted sprayers, may be able to achieve similar savings by refining pesticide applications through the use of laser rangefinder-based spray application technology.
Controlling irrigation using timers or manually operated systems is the most common irrigation scheduling method in outdoor container production systems. Improving irrigation efficiency can be achieved by scheduling irrigation based on plant water needs and the appropriate use of sensors rather than relying on periodically adjusting irrigation volume based on perceived water needs. Substrate amendments such as biochar, a carbon (C)-rich by-product of pyrolysis or gasification, can increase the amount of available water and improve irrigation efficiency and plant growth. Previous work examined two on-demand irrigation schedules in controlled indoor (greenhouse) environments. The goal of this study was to evaluate the impact of these on-demand irrigation schedules and hardwood biochar on water use and biomass gain of container-grown Hydrangea paniculata ‘Silver Dollar’ in a typical outdoor nursery production environment. Eighteen independently controlled irrigation zones were designed to test three irrigation schedules on ‘Silver Dollar’ hydrangea grown in pine bark amended with 0% or 25% hardwood biochar. The three irrigation schedules were conventional irrigation and two on-demand schedules, which were based on substrate physical properties or plant physiology. Conventional irrigation delivered 1.8 cm water in one event each day. The scheduling of substrate-based irrigation was based on the soilless substrate moisture characteristic curve, applying water whenever the substrate water content corresponding to a substrate water potential of –10 kPa was reached. The plant-based irrigation schedule was based on a specific substrate moisture content derived from a previously defined relationship between substrate moisture content and photosynthetic rate, maintaining the volumetric water content (VWC) to support photosynthesis at 90% of the maximum predicted photosynthetic rate. Total water use for the substrate-based irrigation was the same as for the conventional system; the plant-based system used significantly less water. However, plant dry weight was 22% and 15% greater, water use efficiency (WUE) was 40% and 40% greater, and total leachate volume was 25% and 30% less for the substrate-based and plant-based irrigation scheduling systems, respectively, than for conventional irrigation. The 25% biochar amendment rate reduced leachate volume per irrigation event, and leaching fraction, but did not affect total water use or plant dry weight. This research demonstrated that on-demand irrigation scheduling that is plant based or substrate based could be an effective approach to increase WUE for container-grown nursery crops without affecting plant growth negatively.
Container-grown nursery crops generally require daily irrigation applications and potentially more frequent applications during the hottest part of the growing season. Developing management practices that make more efficient use of irrigation water is important for improving the sustainability of nursery crop production. Biochar, a byproduct of pyrolysis, can potentially increase the water-holding capacity and reduce water and nutrient leaching. In addition, the development of sensor-based irrigation technologies has made monitoring substrate moisture a practical tool for irrigation management in the nursery industry. The objective of this research was to determine the effect of switchgrass biochar on water and nutrient-holding capacity and release in container substrates of Buxus sempervirens L. × Buxus microphylla (‘Green Velvet’ boxwood) and Hydrangea paniculata (Pinky Winky® hardy hydrangea). Containers were filled with pine bark and amended with 0%, 10%, or 25% volume of biochar. Plants were irrigated when the volumetric water content (VWC) reached the water-buffering capacity set point of 0.25 cm3·cm−3. The sensor-based irrigation in combination with the low cost biochar substrate amendment increased substrate water-holding capacity and reduced irrigation requirements for the production of hydrangea, a high water use plant. Biochar application rate influenced irrigation frequency, which likely affected plant biomass for hydrangea, but boxwood dry weight was unaffected by biochar rate. Total irrigation applied was decreased by 32% in 10% biochar treatment without reducing hydrangea dry weight. However, in the 25% biochar treatment, total irrigation applied was reduced by 72%, whereas dry weight decreased by 50%. Biochar application reduced leaching volume and leaching fraction in both plants. Leachate analysis over the course of the 8-week experiment showed that the average mass of phosphate (PO4), potassium (K), and total carbon was greater in the leachate from containers that received 25% biochar compared with those receiving 0% or 10% biochar for both plant species. For hydrangea, mass of total nitrogen (TN) and nitrate (NO3) in leachate was not significantly affected by increasing the biochar rate. However, for boxwood, the mass of NO3 and TN was greater in the 25% biochar treatment leachate, whereas the mass of ammonium (NH4) was unaffected. In hydrangea, total nutrients lost from the containers was lower in biochar-amended containers (both 10% and 25% biochar) because of receiving a lower total volume of water. Amendment with biochar also affected concentration of phosphorus (P) and K, with the highest concentration in both leaf tissue and substrate from the 25% biochar application rate.
To optimize pesticide applications to the canopies of deciduous perennial crops, spray volume should be adjusted throughout the year to match the changes in canopy volume and density. Machine-vision, computer-controlled, variable-rate sprayers are now commercially available and claim to provide adequate coverage with decreased spray volumes compared with constant-rate sprayers. However, there is little research comparing variable- and constant-rate spray applications as crop characteristics change throughout a growing season. This study evaluated spray volume, spray quality (e.g., coverage and deposit density), and off-target spray losses of variable- and constant-rate sprayers across multiple phenophases in an apple (Malus domestica) orchard and a grape (Vitis vinifera) vineyard. The variable-rate sprayer mode applied 67% to 74% less volume in the orchard and 61% to 80% less volume in the vineyard. Spray coverage (percent), measured by water-sensitive cards (WSC), was consistently greater in the constant-rate mode compared with the variable-rate mode, but in many cases, excessive coverage (i.e., over-spray) was recorded. The variable-rate sprayer reduced off-target losses, measured by WSC coverage, up to 40% in the orchard and up to 33% in the vineyard. Spray application deposit densities (droplets per square centimeter) on target canopies were typically greater in variable-rate mode. However, the deposit densities were confounded in over-spray conditions because droplets coalesced on the WSC resulting in artificially low values (i.e., few, very large droplets). Spray efficiencies were most improved early in the growing season, when canopy density was lowest, demonstrating the importance of tailoring spray volume to plant canopy characteristics.