Talke cuttings from the vine,and if you still can move it. Cut the original down.Hopefully it will survive and thrive again.Your neighbor is old,and I am hoping that she will be rehomed soon to various elderly housing situations or die. If a person would spray on their fence side knowing it could over spray onto yours I doubt very much they will care if you complain.
In the least I would let her know her spraying is affecting food plants that you and your family eat. The spraying will also affect plants the chickens eat. I would remove all edible things from that area,and keep family/animals away as well. If you want you could contact local police(or a lawyer) to see if she can be cited for poisoning your food?!?!?
She reminds me of an old lady someone was dealing who they dubbed NUTTY. Even with video ,fines,and court orders Nutty kept harassing her neighbors. I think they just had to wait it out till Nutty got rehomed or died.
I would say something even though it might up the anty(sp) by her.Time for a video cam pointed in her direction! Put up some fencing to block off the area. I would want to situate a manure pile in that location as well. Sorry,but I would need some wee bit of *get back at ya* satisfaction for what was done.A 40 year grape vine-should be illegal to kill it!
Politely ask if she sprayed or has seen anyone spraying that area, and discuss your concerns. Perhaps her only intent was to get the grapevine and the wind caught the spray and took it further. If she denies it, then tell her you are going to put up a cam.
Is this grapevine lurking and crawling on her side of the fence? Perhaps that is why she hates it. Wrong to just kill it though.
Most places require fence set backs,so you may actually own a few inches to feet on the other side. My fence is 2 inches in.That means I own the entire fence.Neighbors can weed wack along the fence line if they want,but cutting/spraying the vining plants I grow on the fence is property damage.
You can get a boundary survey just for that section then charge the woman in small claims for replacement of the plant if she refuses to replace it.Ofcourse charge for the court fee as well since a grape plant doesn't cost all that much.Nothing can replace a 40 year plant.
I would let the charging go and just do a survey to ensure who owns what.If the fence was inside the property line I would actually put something up on her side just inside the fence line to block her. Ofcourse a survey could also reveal the fence is off quite a bit or it could be right on the line.Right on the line means you both own the fence.And we all know what it means if the fence is on her side of the line!
I would suggest reading the NFH forums before saying/doing anything.See what others had to deal with when they talked to their neighbors about problems they had with them.
Since she poisoned it right after you moved in several years ago, it's odd that she waited so many years to poison it again.
Did she admit poisoning it to anyone the first time? If so, that would go a long way as far as prosecution, and she should be called to task for it. With the kids and animals there, someone poisoning your property could go a lot farther than just simple plant vandalism.
Around here, people can trim anything growing over onto their property, and if a herbicide is used on their property that results in damage to your property, they're responsible for it.
Fencing laws can be sticklish. Sometimes fences built inside the property line actually just end up giving the neighbor that property after a certain amount of time. Solid fences sure can help, but even then I'd be concerned about something being tossed over it by a person that could set poison out around kids.
I've heard of people cutting across a small corner of your land then after a while they lay claim to it as a right of way if you didn't make an effort to stop them. Crazy stuff.
Set up a camera, but don't tell her.
Get the survey done and check your laws and if you can raise the height of the fence.
Contact law enforcement and get it on a report. Then if this keeps happening and you catch her on the camera you can get her for damages, also she might be having health issues no one is aware of yet.