This blog is dedicated to sharing timely and relevant precision ag information with county Extension agents and growers.

With increased availability and interest in spray drones recently, we are starting to see more people getting into the spray drone application business as well as growers who are interested to learn more about the technology and its application capabilities. The wet weather during months of May and June across much of the southeastern US also made most fields inaccessible with ground application equipment, hence limiting the timely pesticide applications for most growers. Consequently, there have been lot of questions lately about use of spray drones for pesticide applications in both row and specialty crops. While multiple research efforts are underway and it will take some time to completely understand the spray performance and efficacy of pesticides applied with spray drones, we have learned some things from our work that can serve as some general application considerations and helpful for those interested in using spray drones for pesticide applications:  

  • First and foremost, it is important to understand that the rules and regulations for using spray drones for pesticide applications are very different and complex than flying a normal drone with a camera. Make sure you are aware about all the FAA regulations for pesticide applications with spray drones and have all the required licenses and certifications in place. Detailed information on these regulations can be found here:
  • Regarding labels, at this time if a pesticide has been approved for an aerial application, it can be applied with a spray drone following the similar application i.e. spray volume, droplet size and other drift management requirements listed on the label. Changes to pesticide labels for aerial applications with spray drones are expected in the future.
  • For most pesticide labels, remember that the minimum spray volume requirement for aerial application is 2 GPA (check label carefully, this can be higher like 5 or even 10 GPA for some pesticides). Do not use spray volumes below the minimum recommended or 2 GPA as it can considerably affect the coverage and pesticide efficacy, and it can also create compatibility issues during mixing. In fact, we have seen significant improvement in both coverage and efficacy in some cases by increasing the spray volume to 3 GPA.
  • Currently, most new spray drones come equipped with standard XR flat-fan nozzles (except if it has rotary atomizers) which are not really the best choice for spray drift management and even coverage for aerial applications. Use a nozzle that provides medium to coarser spray droplets (e.g. AIXR or AirMix) to minimize spray drift potential as well as attain good coverage on the crop or within the canopy. XR nozzles should only be used in calm conditions with wind less than 4-5 MPH.
  • For spray drones with rotary atomizers such as DJI T40, there is an option to select the droplet size from the controller screen so again make sure to use the medium to coarser droplet sizes as 250 to 320 µm spray droplets is a good range for most pesticide applications.
  • Drone height from the ground or crop canopy is directly related to the spray swath but also only up to a certain height. Determine an optimal height range for your drone, such as 8 to 12 ft. for DJI T30, and stay within that range for adequate application performance. Do not fly too low or too high to avoid streaking or causing any unnecessary drift that could be avoided. Also remember that flying above a certain height (e.g. 12 ft.) do not increase swath anymore but instead considerably increases the potential for spray drift.
  • Most newer spray drones are equipped with a rate controller which means that it will adjust the flow rate (gallons per minute, GPM) accordingly based on the selected speed and swath to attain the target application rate (in GPA) but within the pump and spraying systems’ capacity. Therefore, do not always utilize the maximum swath and maximum speed options for applications as the performance of the spray system is mostly sub-par at its full capacity. The potential for spray drift and vortex is also increased at higher speeds.
  • Before any pesticide applications with your spray drone, it is highly recommended to perform some sort of swath testing using spray cards or a continuous sheet of paper to determine effective swath using the intended application parameters i.e. height, speed and nozzle type/droplet size. This is very important to understand the spray performance (coverage) of the drone and to adjust swath accordingly to avoid any major application issues.
  • The general best management practices for pesticide applications applies to the spray drones too so make sure to follow them accordingly. Some of these include avoid spraying when wind speeds are more than 10 mph, considering wind direction to minimize spray drift, and avoiding applications when conditions for temperature inversions are favorable or if sensitive crops are downwind. 
  • None of the spray drones available today have any sort of agitation in the solution tank so make sure to be careful about using any pesticides that need to stay suspended in the solution or using tank-mixes that can possibly seize the pump or clog the nozzles. If planning to use two or more pesticides, make sure to properly check the tank-mix compatibility of the products using a jar test or other similar method. Tank mix compatibility test is very important for low GPA applications (2-3 GPA). A jar test should be performed when a new tank mix is used. Considering spray drones do not have tank agitation, the tank mix in jar test should be able to maintain homogeneity for at least 8-10 minutes without showing layer separation and precipitation.  
  • Always use a drift reducing adjuvants (DRAs) to improve coverage and also reduce spray drift. Some DRAs can cause foaming and tank incompatibility if they have oil-based formulation. Jar test for compatibility is required when tank mixing a new DRA.
  • Before creating and implementing a flight plan, inspect the field properly for any obstacles or any other operational considerations that will require the drone to stop or veer from the planned flight route. In most cases, using only background maps (aerial/satellite imagery) is not reliable enough to avoid all possible obstacles in the field so in-field checks before take-off are must for safe operations and to avoid any damage to the spray drone.
  • Loss of signal between the drone and remote controller is common when flying large fields or tall crops like corn and creates significant crash risks for the operators. Utilizing signal transmitters like DJI relay can reduce the risk of drone losing the connection with the controller in these situations where the drone is out of sight. It is also important to set up the base on high ground so the drone is in the visual line of sight as much as possible during application.   
  • When planning to spray large acres, think about re-filling and charging station to minimize downtime and be efficient with the application. A portable trailer setup with re-filling and charging stations onboard seems to be the most common practice currently utilized by spray drone operators but this can vary from one operation to another and also based on many factors such as number of batteries, generator capacity, size and type of the fields to be sprayed.  
  • Given the costs of spray drones ($30,000 – 50,000) which will likely increase in the future with larger tanks and more advanced features, consider purchasing a drone insurance especially if planning to operate as a commercial spray drone business. This is also a good option for growers and operators planning to use them for pesticide applications on their own farms.

Note: Any company or product names mentioned by the authors are just for informational purposes and do not imply endorsement of their products or services.