Re: What now? Disc won\'t penetrate
There appear to be some misconceptions here about Roundup. I am not an expert, but this is what I do know:
Roundup will kill almost everything, depending on when it is sprayed. Blackberries here in the northwest seem to be the most timing dependent and should be sprayed in the fall.
Roundup works by being taken through the leaves, then translocated through the plant to the roots, which it kills. It may kill other parts, but it is the root kill that seems to do the job. What this means is that you can plant almost as soon as the roundup is dry, because it is not a soil active herbicide. In fact the soil deactivates any that lands on it.
The reason that blackberries should be sprayed in the fall is that earlier in the year most of the stuff in the plant is moving from the roots to the leaves, where the herbicide does almost nothing. In the fall, the plant starts packing food down to the roots for the winter to build up reserves, and the roundup goes along, too and does it's job very well at that time. Grass and many other plants seem to move stuff both ways all the time, so timing with them is not important.
Always use a wetting agent (surfactant) with Roundup or any herbicide & you'll see much better results. Spend the money on the commercial stuff; putting a little detergent in with the spray doesn't do the job.