2018 ASHS Annual Conference

Novel, variable-rate spray technology was developed that can be retrofitted to existing airblast sprayers. The sprayer applies pesticides based on real-time scanning laser rangefinder measurements of plant presence, size, and density. The objective of this experiment was to evaluate spray coverage and deposit density at four application rates applied to Malus domestica ‘Golden Delicious’ apple trees from the newly developed technology.

Uniform trees in two 408-ft long rows running in an East-West orientation were used for this study. Four pairs of trees, the 3^rd, 15^th, 25^th and 35^th trees, across the driveway from one another were selected, and four clips for water sensitive cards (WSCs) were placed equidistant from one another within each canopy. Clips were attached to branches at increasing distances from the driveway at a height of 170 to 180 cm from the ground. One of four rates, 0.03, 0.05, 0.07, or 0.09 fl oz/ft³, was randomly assigned to each pair of trees within the row so that all four rates were tested on each run. WSCs were placed in the clips, and the trees were sprayed with water. Rates were randomly re-assigned to trees, and a WSC was placed in each clip prior to each of the three subsequent runs. Cards were analyzed for coverage (%) and droplet density (deposits/cm²).

There was an orientation effect on sprayer performance due to wind direction. Coverage was 24, 16, 10, and 3% greater for cards 1, 2, 3, and 4, respectively, on the North set of trees compared with the South set. In the North row of trees, card position 1 had 35% more coverage than card position 2 and had 47% and 209% greater coverage than card positions 3 and 4, respectively. Similarly, card position 1 in the South row of trees had 26% more coverage than card position 2 and had 30% and 159% greater coverage than card positions 3 and 4, respectively.

For all rates, increasing distance between the sprayer and card position increased droplet density for trees on the North row, likely due to the heavier coverage on the North side causing droplets to coalesce on the cards in closest proximity to the sprayer. On the South row, droplet density was relatively consistent across the canopy at the 0.03 and 0.05 fl oz/ft³ rates but increased with increasing distance from the sprayer at the higher two rates.