What you actually need
Most commercial agricultural drone work starts with the General VLOS Certificate (GVC), which lets you apply for a CAA Operational Authorisation. The heavy spray and spread drones used on farms weigh more than 25 kg in use, so they fall outside the standard permission and need a bespoke authorisation built on a Specific Operations Risk Assessment. Spraying pesticides also requires Health and Safety Executive approval, because it counts as aerial spraying. In other words, a course is one piece of the picture: plan your qualifications around the services you actually intend to offer.