Crop ruined. What to do next year to avoid this?

My best idea is to grow indoors. You can grow bagseed into awesome bud. Every time I've grown outdoors, I've either fought pests, thieves, or cops.

 

Did you prepare the soil in any way, test the ph at least? If the soil's ph was too high it cuold have caused a high ratio of hermies, which would make sense if two out of three are full of seeds. If each or every other branch on an offending plant producing just one or two quite-well-hidden bananas, it's enough to give you a fair few seeds on each branch, and not much for seed elsewhere. The fact that third one seems seed free, makes it unlikely (but not impossible) that the pollen came from elsewhere. There is always that chance it was one of those hard-to-polinate females, but even so.. we'll probably need more info about the soil and surrounding environment before we can give any more solid advice.

 

There's not much you can do, for the most part it isn't a problem, there was an old theory that, outdoors, a male plant can pollinate any female within a 1.5 mile radius due to the wind. But it's an outdated theory, one that I've never seen proven. I'm sure a barrier method (lol.. plant condoms) may help to some degree, but it's not going to stop pollen from drifting in from above, and you need that open for sunlight, unless you plan on building a clear roof too, but that makes it a greenhouse which defeats the purpose of the guerrilla grow

I'd say the problem was closer to home than you'd think, I have a fair bit of breeding experience, I'll pollinate and have males within a grow space, fans blazing, and see only the immediate surrounding plants effected by the pollen, sure sometimes a particularly robust male and pollinate the entire room intended but even then it sometimes won't without manual direction and help.

I generally have two to three rooms running at any given time, all within one small building. I'll fill one grow space with a robust pollen-dropping male and several breeder fems, and sometimes even the females within the room on the outskirts won't pick up the pollen so easily, and I absolutely never see a transfer of pollen from one room to another.

What I'm trying to say is, odds are the pollen was either created locally within the grow area itself, or possibly it was brought there on the body of an animal.

That's all you can hope for anyway, because if there really is another farmer working that nearby leaving males up to produce pollen, and it's really close enough to effect your crop, there's not a whole lot you can do for protection.
If you find no signs of self-pollination, none at all, try a different location next year, that's your best bet.

On the up side, if they didn't pollinate themselves, and you know it for a fact, the seeds may not be useless, (unless of course the other farmer has a hermie, and that's where the pollen came from).. if they were hermie seeds, and they went over so easily, you'd never want to germinate any of them because, genetically, all the offspring will see their parents hermaphroditic breeding being rewarded when they're allowed to live, and will try to carry on the same traits.. ie, the ability to easily produce seeds without the need of a male counterpart.
It's the females that needed to be tortured nearly to death before producing male pollen that are good for hermie breeding, because their offspring will need the same amount of duress in order to produce seeds.

 

You can always just finish them and make hash or butter from them. That is to bad thou a friend had this happen to him last year and made butter.