Within five years, max.
Ground equipment is is already cutting into the agplane jobs, by making extra high clearance rigs with ever wider spray booms. A farmer (that I drive truck part-time for) in Lawrence county TN has bought a extra high clearance Hagie sprayer, and thinks he may rarely hire the agpilot from now on.
The Hagie link shows the tech is amazing, even using boom cameras to identify weeds for spray nozzle control.
https://www.hagie.com/equipment-categories/sprayers/
John Deere ‘see and spray’ system:
https://www.deere.com.au/en/news/all-news/see-spray-premium-available-on-hagie/
Aerial applicators can’t fly slow enough for such precision that can greatly reduce chemical usage.