This tube finally defeated the little critters. The birds are delighted.
Loss: Canadian thistles 50: Sally 10
This view of the Canadian thistle root systems tells the whole story of why it's so hard to discourage them in the garden. You can't pull them out, which only stimulates the roots to send up 10 more in its place. I'm gaining ground in the entire battle, but like some of our skirmishes in foreign lands, I'm not sure I will ever win. I may need to accept that it will go on for years.