Weed presence continues to reemerge year over year, chemical costs continue to increase, and chemical usage continuing to face increasing government oversight, are just a few of the challenges that site-specific weed management intends to address by minimizing wasted application of chemicals and reducing environmental load of active ingredients. Thus, sprayer system manufacturers have developed precision spray systems that allow the individual spray nozzles to be controlled precisely. These spray systems are designed to reduce the waste of overspray, which helps to minimize costs while still providing adequate protection.

To obtain accurate chemical application, precision spray systems with a high level of nozzle control can be utilized for weed management. There are several factors affecting herbicide application with the performance of the spray application system playing a determining role in the final herbicide coverage. Compared to sprayer systems that have large sectional control, there are not many studies conducted on the resolution or minimum cell size required to utilize the full capability of the sprayer systems that offer individual nozzle control. An optimum cell size or resolution for the spray prescription map could help producers plan their site-specific weed management (SSWM) herbicide application while still guaranteeing coverage.

The goal of this project is to determine an optimum cell size or resolution for a prescription herbicide application map, which guarantees acceptable coverage needed to eliminate the weeds identified from unmanned aerial system (UAS) imagery. The major objectives of this study were 1) to determine an optimum prescription map cell size/resolution that is compatible with current technology, and 2) to assess spray accuracy by comparing the prescription map to the as-applied map recorded by the sprayer system.

The studies were carried out at the NDSU Carrington Research Extension Center (CREC, Carrington, ND). The test site was mapped using a Phantom 4 RTK to collect georeferenced imagery with high spatial accuracy, which was later used as the background for creating the prescription maps.

Prescription maps were first created as shapefiles in ArcGIS Pro, then exported to AgSMS Advanced, and them exported as Rx maps. In this studies we evaluated the effect of cell length (0.5, 1.5, and 3 m long), and spraying speed (7.1, 10.3, and 13.5 km/h) combined with cell length (1.5, 3.05, 4.6, and 6.1 m) on spraying accuracy when using Case IH Patriot 4440 sprayer equipped with individual nozzle control, Raven Viper 4+, and RTK receiver.

The outcomes show that the dependent variables cell width and application speed had the greatest effect on application accuracy (p-values < 0.05), and that an optimum cell width of 1.5 m , a length of 3.05 m , and application speed of 10.3 km h^-1 is recommended.