INTELLIGENT SPRAY SYSTEMS FOR FLORAL AND ORNAMENTAL NURSERY CROPS
Location: Application Technology Research Unit
2012 Annual Report
1a.Objectives (from AD-416):
To develop two advanced and affordable spray systems that employ intelligent technologies to continuously match system operating parameters to crop characteristics, insect/disease pressures and microclimatic conditions during pesticide applications.
1b.Approach (from AD-416):
Will develop two intelligent expert precision spraying systems implementing five main components to apply the amount of pesticides as needed. The first system will be an air-assisted variable-rate sprayer to be used for shade, flowering and ornamental trees in nurseries. The second system will be a hydraulic boom variable-rate sprayer to be used for flowering container plants in greenhouses and woody ornamentals in nurseries. Due to the similarity of crop structures, the use of the first system can be expanded to other specialty crops such as fruit trees and vineyards, and the second system can be expanded to berries and vegetables. The five components will be: a sensor-controlled unit to control spray outputs that match structures of specific floral and nursery crops, an expert subsystem to assist choosing proper chemicals and application schedules, a direct in-line injection unit to inject concentrated chemicals to individual nozzles to eliminate leftover disposals, a off-target recovery unit to prevent spray off-target losses including drift beyond target areas, and a fluid delivery subsystem to discharge spray outputs with variable rates. All the operations will occur as the sprayer moves past the canopy, providing uniform spray coverage of the canopy with minimum pesticide use and off-target loss beyond the target area. Speciality Crops Research Initiative.
Air jet velocity distributions from an air assisted, five-port sprayer, which was in the development process to achieve variable rates of both liquid and air, were measured at various locations in an open terrain and inside tree canopies. The air jet velocity was controlled by changing the sprayer fan inlet diameter and was measured with a constant temperature anemometer system coupled with hot-film sensors. Sprayer travel speed ranged from 0 to 8.0 km/h. When the sprayer was stationary, the axial air velocity increased as the fan inlet diameter increased while it decreased in the hyperbola function with the increase of distance from the nozzle outlets. When the sprayer was on the move, due to the air entrainment and air jet diversity, the peak air velocity decreased with the increase of distance from nozzle outlets. The peak air velocity also increased as the fan inlet diameter increased but the increase scale was not as great as the increase scale of the fan inlet diameter. Variations in the peak air velocities with the tree volume and foliage density were significant. There were little variations in the peak air velocity with the travel speed and measurement height, confirming the sprayer was able to achieve variable air flow rates for different canopy sizes and foliage densities by controlling the fan inlet diameter.
An electronic flow rate control system with microprocessors and pulse width modulation (PWM) controlled solenoid valves was designed to manipulate the output of spray nozzles independently to match tree structures which would be detected with a wide-range laser scanning sensor. The PWM signals to control nozzle flow rates were generated by the microprocessors based on laser sensor detections. Multi-channel driver and protection circuits for activating solenoid valves were developed to modulate variable-rate outputs in real time. An embedded computer (PC/104) along with a touch screen was used to process control algorithms and to fulfill communications between the operator and the control system. Laboratory tests demonstrated that the flow rate control system was able to achieve linear nozzle outputs with the duty cycle of PWM-controlled solenoid valves.
A variable-rate air-assisted sprayer implementing laser scanning technology was evaluated in an apple orchard by quantifying spray deposition at three different growing stages (April, May and June) with three sprayer treatments: the new variable-rate sprayer (S1), the same sprayer without the variable-rate function (S2) and a conventional air blast sprayer (S3). Their spray coverage and deposits inside canopies were measured and compared with water sensitive papers and nylon screens. The three sprayer treatments provided fairly consistent spray coverage and deposit in spray direction (or canopy depth direction) in April test when tree foliages were in the early growth stage. The variations in spray coverage and deposit in spray direction increased considerably for S2 and S3 in May and June tests. S1 produced better uniformity in spray deposit and coverage across tree height direction than S2 and S3 at all growth stages. Compared to conventional constant-rate sprayers, the new variable-rate sprayer only consumed 27% to 53% of the spray mixture while it still achieved adequate spray coverage inside canopies. Also, the spray deposition from the new sprayer was very consistent regardless of the canopy growth stages. The new sprayer was able to apply appropriate amount of pesticides based on tree canopy characteristics such as tree height, width, volume, foliage density and occurrence of trees, and thus increased spray efficiency and improved spray accuracy, resulting in reduced spray costs and potential environmental pollutions.
Field efficacy tests were conducted to evaluate the control of aphids and powdery mildew by use of newly developed ultrasonic sensor controlled variable-rate sprayer in a commercial nursery in Oregon. The control efficiency was also compared between the new variable-rate sprayer and a conventional constant-rate sprayer. During the growing season, application rate of the conventional sprayer was 75 to 100 gallon per acre while the variable-rate sprayer used less than 35 gallon per acre. For aphid evaluation, leaves were randomly selected from the top, middle, and bottom of the red oak tree canopy for a total of five leaves each from 10 different trees in each row, and the total number of aphids from both the top and bottom of the leaves were counted. For assessment of powdery mildew, Norway maples were selected and sampled weekly throughout the growing season. The rating system used a visual assessment of percent coverage of powdery mildew mycelia on both sides of the leaves. These field tests were a paired comparison experiment with the randomized block design. Ratings of powdery mildew fungal sporulations on five leaves of each tree were averaged to represent an observation for statistical analysis. Observations of 20 trees in two rows for each rating day were grouped to calculate the mean rating for either a smart or conventional spray treatment. The mean ratings for powdery mildew between the two treatments for each rating day was then analyzed with Fisher’s least significant difference (LSD) multiple comparison test and tested at the 0.05 percent level of significance. The difference between the averaged rating means of the two treatments from the first rating to the last rating during the growing season was also analyzed with the Fisher’s LSD multiple comparison test and was verified with the t-distribution of differences between rating means of two treatments on the same day. Aphid numbers on five leaves of an oak tree on each rating day and during the growing season were similarly analyzed and significant differences between the smart and conventional spray treatments before and after insecticides treatments were determined. Test results demonstrated that there was no significant difference to control aphids or powdery mildew between the conventional and new variable-rate sprayers while the new sprayer used two to three times less chemicals than the conventional sprayer.
This project addresses critical elements for the development of precision sprayer technology envisioned in ARS parent project Objective 1 “Develop precision sprayers that can continuously match canopy characteristics to deliver agrichemicals and bio-products accurately to nursery and fruit crops.