Improving Spray Quality and Disease Control with a Laser-guided Air-assisted Sprayer for Multi-row Nursery Production

In Tennessee, nursery producers often maximize production areas by planting 4 or more rows in a block.  While this increases the production area it can affect pesticide spray deposition quality and pest control.  Nursery producers can choose from many sprayer types depending on target application. Typically, air-assisted sprayers are preferred when applying fungicides and insecticides to field crops.  Conventional air-assisted sprayers can be used if there are no concerns for excess pesticide use and/or drift; however, this is increasingly not the case as negative effects of non-point source pollution have become more widely recognized and pesticide costs have increased.  The objective of this experiment was to compare spray coverage, spray drift reduction and powdery mildew control in multi-row nursery blocks between a newly developed air-assisted sprayer guided with a laser scanning sensor, which was designed to control spray outputs to match canopy structures and greatly reduce pesticide application volume, and a conventional Tifone Storm 1500 air-assisted sprayer.  The experiment was conducted at Walker Nursery, Morrison, Tennessee.  Prior to initiation of the experiment early symptoms of powdery mildew were scouted weekly.  At the first sight of symptoms, Cornus florida ‘Cherokee Princess’ trees were rated and spray comparison tests were initiated.  On day of application, 2 sets (1 set = 2 cards back to back) of water sensitive cards were placed in 5 trees per replication per treatment (n = 120 cards); one set was used to record spray drift and the second was used to document spray coverage.  The experiments were conducted using a randomized complete block design.  Percent spray coverage was 43.5%, 30.7%, and 17.4% in trees sprayed using the conventional sprayer compared with 15%, 21.6%, and 10.2% coverage from the laser guided sprayer, for the three spray dates.  Drift created by the conventional sprayer was greater than drift from the laser-guided sprayer at each application date.  Overall, powdery mildew ratings were not different with the exception of the third week following the first application.  Powdery mildew was generally no different on trees in the interior of the block from exterior rows indicating the sprayers penetrated the interior of the block equally well.  Younger leaves had lower levels of powdery mildew than the oldest leaves for the first 7 weeks of the study.  These results indicate that growers with multi-row production blocks can potentially benefit from laser-guided technology by reducing pesticide use and spray drift without sacrificing plant quality.