My plot was an array of fields 5x6. A field against the wall developed Crow-damage. But I never saw a crow, and I think it was outside the wall. If so, then I need to run outside my walls, to chase all crows off? Hopefully not, that would be an obnoxious grind.
The 600% upkeep was an inconvenience, but didn't ruin the field. It took about 10 humus (maybe more, I was spamming it), and then 300 cotton seeds to plant it. Then before any fertilizer, the upkeep went to 100%, and all fertilizer worked normally. (Had to make my first planter's bag to be able to use 300 seed on one field).