Herbicide Applications with Drones: Stay On-Label and On-Target!

Applying herbicides with drone sprayers has the potential to benefit Pennsylvania growers. Compared with ground-based sprayers, drones may be more efficient in small, irregularly shaped fields, reduce crop damage from sprayer wheel traffic, and enable more timely sprays when wet fields prevent ground-based applications. However, drone spraying technology is moving fast, and policy guidelines and best management practices have yet to be fully developed. Here are important considerations when exploring drone spraying technology for your weed control program.

Label considerations: Applicators should consult herbicide labels to determine whether herbicides can be applied using unmanned aerial vehicles (UAVs), such as drones. State regulatory agencies determine whether drones may follow aerial labels. In Pennsylvania, it is legal to apply herbicides using a drone if the product is labeled for "aerial applications".

Applicators must also determine if label restrictions for aerial applications can be followed when using a drone. For example, the drone application must meet or exceed the minimum spray volume (gpa; gallons per acre) specified on the label. In some cases, herbicides labeled for aerial applications are Not Labeled for ultra-low spray volumes (less than 4 gpa), which are frequently used in drone-based pesticide applications. Aerial labels may also have restrictions on the height of application and the nozzle type (or droplet size) that drones must follow.

Targeted spraying: The following table lists common corn and/or soybean postemergence herbicide products that may be considered for use in targeted drone applications. This table includes whether the product is labeled for aerial use, the minimum required carrier volume (gpa) for aerial applications, and corn and/or soybean growth stage restrictions (or pre-harvest intervals; PHI) for herbicide use.

Applicator certification: On your own or your employer's land, general-use herbicides may be applied without an applicator license- but a private applicator license is needed to apply restricted-use herbicides (RUP) when producing an agricultural commodity. A commercial or public applicator license and the aerial applicator category (Category 25) is required to use a drone to apply either general- or restricted-use herbicides on the property of others, or on other public use sites.

Weed control considerations: Little information is currently available on weed control efficacy and drift potential using drones for herbicide applications. Early research suggests that (1) spray volume and height above the canopy influence weed control efficacy, while operation speed has a smaller effect; and (2) drone-based applications result in greater drift than ground-based broadcast applications. Mitigating drift is a balancing act between choosing an effective, economical spray volume and spraying in less predictable draft, wind, and weather conditions.

Understanding how drone application factors influence "spray quality", including droplet size, swath overlap, and coverage (%), will be important for calibration and developing best management practices. Adequate spray coverage is particularly important for maintaining weed control efficacy of soil-applied residual (PRE) products, as well as foliar-active (POST) products that have contact activity.

Drone herbicide application checklist: Before using a drone for a herbicide application, we suggest using this checklist:

1. Does the state regulatory agency allow drones to be used under the aerial label?
2. Does the herbicide product of interest have an aerial label?
3. Does the applicator certification level meet requirements for herbicide product(s)?
4. Can drone use and output meet the minimum carrier volume (gpa) for aerial use on the label?
5. Can Drone use meet other restrictions (e.g., height above canopy, nozzle type) on the label?
6. Will the drone application adhere to application restrictions based on crop growth stage?