Cat. I know several will caution against this but I use a regular strength light spray of roundup. Do not spray right up to the cane. Stay at least 6" away. As a precaution I never apply when the ground is wet and when the plant has berries on it. I have never had a problem. Be extra careful with wind drift. Try at your own risk but I can say it has worked for me. Good luck Bill

I think that's vetch and it is hard to eradicate since it is spread from underground runners. Are you using the pine needles as mulch? Make sure it doesn't acidify the soil too much for your blackberries.

How many blackberry plants do you have? It might be worth it to dig them up and get rid of all traces of the vetch and replant. Then put some weed barrier down to keep it from getting out of hand in the future.

I'm new to raising blackberries and have been using pine needles as a mulch (should I use something else). I only have 10 plants all on a trellis already with nice laterals. I quest I can rake up the pine needles and pull as many weeds as I can and put some weed barrier down, this would help so I wouldn't have to worry about spraying. I guess I also need to check the PH again.

I don't think it's vetch. Looks more like Phyllanthus urinaria - Chamber Bitter.

Here is a link that might be useful: Phyllanthus urinaria - Chamber Bitter

^You're probably right, floral...we don't have that plant here but we certainly have vetch. ;)

We don't have it either but it has been asked about a few times on Garden Web so I remembered it.

Here is what I ended up doing, I put down some silt fence from Lowes and left a 2' open strip for my blackberries. I can now spray all the rest of the island without hurting the blackberries and pick any weeds along the 2' open strip.

Picture after putting down pine needles, I think I'll put down my mulched leaves this fall so I don't have to keep paying for pine needles.

Contrary to popular myth Pine Needles do not significantly affect soil pH. The simplest means of control of those "weeds" is a cultivator.
Those that advocate using glyphosate products may want to read the link.

Here is a link that might be useful: About glyphosate

This post was edited by kimmsr on Thu, Jul 17, 14 at 7:01

If you can stay on top of pulling the Phyllanthus this year, you should have many fewer next year, they're an annual. It's a deceiving plant because it never makes visible flowers, and its' seed balls are under the foliage. Pulling them before the seeds ripen and fall is the best course of action.