2019 ASHS Annual Conference

A recent groundbreaking advance in spray application technology, the ability to customize the application using scanning laser rangefinder measurements and variable-rate solenoid valves can be retrofitted to existing air-blast sprayers, allowing growers to access the technology without purchasing a new sprayer. This technology detects plant presence, size, and density and adjusts spray output to match crop characteristics in real-time. Multi-row blocks provide a unique performance environment for the laser-based sensing system; therefore, the objective of this experiment was to compare sprayer performance and volume, and pest and beneficial insect populations in the manual and “intelligent” spray modes when applied to 15-gallon trees in a multi-row block, pot-in-pot production system.

For this experiment, a field was divided in half, with one half sprayed in intelligent mode applying 0.07 fl. oz./ft³ (0.07 L/m³) and the other in manual mode applying 51.3 gallons/acre (480 L/ha), a conservative rate compared with the industry standard of 100 gallons/acre (935 L/ha). Ten Shumard oaks were flagged in each treatment and monitored regularly for Cylindrosporium and Tubakia leaf spots. Half of the trees were in an outer row of a block and half in an interior row. Presence and number of pollinators and natural enemies were also recorded. On August 8, 2018, water sensitive cards were placed in the tree canopies and at the base of flagged trees and then sprayed with water to assess intentional and non-target spray with one pass down the driveway, spraying cards from one direction. Cards were analyzed for coverage (%) and droplet density (deposits/cm²). Spray volume consumed was recorded for each treatment (sprayer mode).

Shumard oaks increased in caliper 0.05 in (1.3 mm) and 0.12 in (3.0 mm) for the manual and intelligent modes, respectively, from August 4 to November 16, 2018 and were not affected by sprayer mode or row position (P-values 0.0548 and 0.5008, respectively). The average spray volume consumption was 102 gallons (387 L) for the manual and 72 gallons (272 L) for the intelligent mode, a 30% reduction (P-value <0.0001). Pest population levels and pest damage were managed to an acceptable level in both treatments. Few natural enemies and pollinators were observed, regardless of treatment. Within the canopy, pesticide application deposit density met or exceeded the recommended guidelines for both modes (20-30 droplets/cm² threshold for insecticides, 50-70 droplet/cm² threshold for fungicides). Coverage and deposit density did not significantly differ between sprayer modes (P-values >0.05); however, volume used in the intelligent mode was significantly less indicating the intelligent sprayer technology can achieve recommended pesticide application ranges while reducing pesticide costs and the potential for negative ecosystem impacts.