On the surface, the concept of using a small unmanned aircraft system (sUAS) to apply chemicals seems a bit crazy, but in specialty crop production such as nurseries, this method of applying chemicals by air makes great sense. Currently, the ground-based application of chemicals is the standard method in nursery crop production. Existing spray systems do not efficiently deliver pesticides within dense nursery crops and require the applicator to be in close proximity to the target site. Additionally, conventional spray systems apply chemicals across the entire taxa or nursery regardless of pest pressure resulting in excessive amounts of pesticide use to achieve effective pest control in isolated hotspots. Enter the small (take-off weight less than 55 lbs) unmanned spray drone (Fig. 1).
This rapidly evolving technology offers advantages over current application methods such as reducing the cost of chemical application and environmental impact, reduced drift, reduced operator exposure, and improved ability to make applications in a timely and highly spatially resolved manner. sUAS also have the capability to fly repeated autonomous flight paths by using multiple stored waypoints (GPS point), resulting in easily repeated applications to specific blocks or hotspots. Also of interest to growers is the application of granular products (e.g., fire ant bait), which is a novel concept in sUAS pesticide application. One advantage of granular applications over liquids is the possibility to carry more payload due to the reduced weight (i.e., lower bulk density). Application of granular fire ant baits is low hanging fruit because the material is applied in non-overlapping lanes which can be efficiently planned for using existing flight navigation software. To give you an example of a granular application, the USDA recently tested grasshopper control in New Mexico using granular carboryl bait applied at 5 pounds/acre on a 50-foot swath and each flight covering 5 acres (Fig. 2).
Many would say that this concept (i.e., small spray drones) is not feasible. However, it is currently operational in 32 states for activities such as vector control, weed management, and industrial applications. Applicators are treating up to 250 acres a day with a single system. Spray drones are a forerunner for the assimilation of autonomous equipment into agriculture production systems. While this article focuses on spray drones in nursery production, this technology will prove very useful in other specialty horticultural crops (e.g., vining vegetables such as watermelon and cucurbits, turfgrass, strawberries) where intensive pesticide application is employed.
Several suppliers (e.g., Leading Edge Aerial Technologies, HSE-UAV, Hylio) in the U.S. sell various aerial application drones that can apply liquids or granules. Manufacturers have adapted quickly to this rapidly advancing area by developing interchangeable tanks/reservoirs for safety and convenience issues. Manufacturers are also developing chemical loading systems for the safe handling of pesticides. Newer models include RTK (real-time kinematics) GPS capability, allowing for ultra-precise GPS positioning within 3 cm accuracy. An important new feature of most models is obstacle avoidance technology. This technology enables the sUAS to sense and avoid obstacles in the field such as trees, power lines, irrigation systems and the like.
As with any emerging technology, there are many issues that need to be considered before widespread adoption is possible in the U.S., including regulatory and labeling. To fly sUAS in the U.S., you must be remote pilot certified (Part 107), but since we want to use these aircraft to apply chemicals, you must also obtain Agricultural Aircraft Operations Certification (Part 137). These are the same regulations that apply to operators of manned spray aircraft, so during the application process, you will request waivers for sections that do not apply to unmanned aircraft. The Part 137 certification of sUAS is new for the FAA, so everyone is adjusting to the process. Another issue is the labeling of chemicals that you wish to apply using sUAS. Again, this is new territory for chemical manufacturers and the EPA, so everyone is slowly navigating the process.
As with other aspects of sUAS, we will see many companies respond to the increasing demand by offering spray services to nurseries. As with other types of sUAS applications (e.g., generating aerial images, generating vegetation indexes), utilizing these service providers may be the best option for a nursery since these companies already have the licensing and equipment in place.