2018 ASHS Annual Conference

A variable rate sprayer was developed that applies pesticides based on real-time scanning laser rangefinder measurements of plant presence, size, and density. The objectives of this experiment were to evaluate (1) control of dogwood powdery mildew and (2) characterize spray applications to Cornus florida in a multi-row block from the newly developed laser-guided “intelligent” sprayer and a conventional air-blast sprayer.

Water sensitive cards (WSCs) were placed in ‘Cherokee Princess’ flowering dogwood trees prior to each of four fungicide applications to characterize spray penetration and drift. Cards were analyzed for coverage (%) and droplet density (deposits/cm²) using the DepositScan program. Powdery mildew severity was ranked weekly throughout the season. Whole trees were rated on a 0-4 scale following Hagan et al. 1998 with 0 signifying no disease and 4 signifying 76-100% disease.

Increase in plant height over the season was 49 and 48 cm for the intelligent and conventionally sprayed trees, respectively, and increase in caliper was 13 and 10 mm for the intelligent and conventionally sprayed trees, respectively. On May 26, June 28, and July 27, 2017, the overall tree disease ratings were 0 and 0, 0.75 and 0.625, and 0.58 and 0.50 for intelligent and conventionally sprayed trees, respectively.

Intentional spray coverage and droplet density on WSCs were lower from the intelligent sprayer than the conventional sprayer by 47 and 59%, respectively. The average deposit density was within 6.5% of the recommended range for fungicides when spray was applied by the intelligent sprayer but was 38.3% from the range when applied by the conventional sprayer. Drift coverage was reduced 63.5% by using the intelligent sprayer.

The intelligent sprayer reduced spray volume by 53.7% compared to the conventional sprayer. The average per application cost for this trial was $5.07/2.4 acres for the intelligent sprayer and $14.95/2.4 acres for the conventional sprayer, a 66% cost reduction from using the intelligent sprayer. A second generation intelligent sprayer that can be retrofitted to existing air-assisted sprayers is currently under evaluation.