Agricultural pilot reported an airborne conflict with a UAS that was crop-spraying in a nearby field. The pilot took evasive action to avoid a possible collision.

Narrative

I was conducting a aerial application flight on a field 17 miles north of ZZZ. When I arrived to the field I circled it several times to look for obstacles. While doing this recon I noticed a truck parked 1/4 mile south of the field. I circled again and noticed that it was a Unmanned Spray Drone operator conducting an application on that field. At the time he had just landed the drone on the back of the truck. I did not see an issue since I would be a 1/4 mile away; and also that I was under the assumption that the drone would stay down low in the field since they were in fact spraying that field. So I proceeded with my application. I flew my field using east/west passes. After about 15-20 minutes I was done but still had to make a trim pass on both ends of the field. Those would be done north/south in this case. I did the west side first; circled around to the North and finished with a southbound pass on the east side of the field. As soon as I pulled up out of the field from that pass; I saw the drone at my 2 o'clock; about 80-100 feet above me; at maybe 1;000 feet horizontally at the most. I abruptly pulled up to further ensure I wouldn't hit it.The issue here is that the drone should never have been at that high of an altitude in the first place. A spray drone flies low in the field just like we do; so it should not have been a factor in this case. They are too hard to see until you are very close. I also circled the operator at roughly 300-400 feet AGL several times so they had to know of my presence. If they had any reason to fly the drone that high they should have waited until I had left the area at the very least. Why they did this I have no idea but had I have been in a slightly different angle on that pass I would have almost for sure hit the drone.Drone operators should yield to manned vehicles at all times. It should be their responsibility to stay clear and keep separation. I am not exactly sure what needs to be done about this; but low flying pilots of any kind need to remain vigilant.