Every year we spot spray for thistles with 2,4-D. In the past that seems to have kept them under control, almost to the point where by July, we have hardly any in the pasture. We do what we can with them, but we have neighboring pastures where the owners may spray once, or not at all. This year, my sister and I have been out in full force spraying with 2,4-D and Hired Hand since the beginning of May. Usually by now, we only have to spend a couple hours a week spraying, but this year we have been spending 4-6 hours every day spraying. The thistles are bigger than ever, some being 3 feet across at the base. After a couple days of being sprayed, the thistles are barely wilting and the grass around them is being burnt. So my question is, can thistles become immune to 2,4-D? Is there something better we can be spraying on them?