42 - Considerations for Effective Aerial Adulticide Applications

Aerial adulticiding is a method used to effectively treat large areas infested with actively flying mosquitoes, either disease vectors or pestiferous species, without the need for a tight street network. However, unlike truck adulticiding which places the spray cloud directly into the target zone, aerial adulticiding relies on a combination of factors to move the spray cloud both horizontally and vertically from application altitude, typically between 100 and 300 feet, to the target near ground level.
These factors include:

< !        1) Aircraft vortices which entrain the spray droplets and then descend between 50 and 100 feet below the aircraft flight level                  before their energy decays to near zero. The strength, longevity and descent distances of the vortices are primarily                            dependent on aircraft characteristics such as size, weight, wing loading and forward speed, with larger slow-moving aircraft              producing stronger vortices.

< !        2) Atmospheric turbulence in the form of both horizontal and vertical air movement. Atmospheric stability describes the level of              turbulence present in the atmosphere, a stable atmosphere being characterized by little to no vertical air movement, a                      condition common soon after sunset on clear calm evenings. By contrast, a neutral atmosphere occurs on windy overcast                evenings and is characterized by moderate turbulence that causes a significant vertical mixing of the spray droplets within                the air mass.

< !        3) Droplet sedimentation energy, which although relatively low (10’s of feet per minute), can be of significance in bringing                      droplets down under stable atmospheric conditions with little vertical air movement.
Consideration must also be given to obstructions within the target habitat, such as forest canopies, which can limit horizontal movement of the spray.
This presentation describes how these factors influence spray movement under different operational settings, an understanding of which is vital in planning accurate and effective aerial adulticide applications.