I live near the Canal du Midi too, and have my boat there. We have been sailing the canals since 1980.
I fail to understand what VNF are trying to do, but I'm beginning to cotton on.
They poison infected trees by injecting them to hasten their demise. The trees they inject don't look anywhere near being on the point of falling down or being even slightly dangerous. There are many trees covered in ivy, which will eventually kill them, but this is totally ignored.
Gangs of people with big machinery eventually come to cut down the trees. After felling them they laboriously cut them up on the canal bank, with (presumably infected) chippings going everywhere, then make a big show of wrapping the logs in plastic sheet to cart them down the road a short way to make a big bonfire with them.
I think the big clue is that somebody is making a lot of money out of this operation.
They put up ludicrous signs saying they are saving the trees by cutting them down. In truth, I think someone's brother-in-law is making a fortune.
Here is a friend's website dedicated to the subject http://www.canaldumidi.net:80/
On some great and glorious day the plain folks of the land will reach their heart's desire at last, and the White House will be adorned by a downright moron.
H. L. Mencken 1880 - 1956
Some may not like his views, but what a prediction!