It's a crop duster. That right there narrows the HAZ-MAT.

Herbicide or pesticide. Ask at his point of origin, or ask the farmer he was working for.

If herbicide -- not so bad.

If pesticide, depending on type, could be semi - to sorta bad.

Materials are more than likely in liquid form - they were crop dusting. Contiain and Clean up and neutralize, according to package directions.