A spray for broadleaved plants will not kill the narrowleaved grasses beneath the blackberries. "2,4-D" is the common chemical name found at the garden centers and is one of the least expensive sprays.
However, this drifts. It'll kill or twist other broadleaved plants nearby.
To kill the plant directly, apply Roundup, to the plants you want to kill ONLY. This will kill all green plants. It's more expensive than other plants.
If you don't want to use chemicals, these can be forked out of the ground. I would use a 4 tned "potato fork". But, roots will sometimes (often) spring up. Mowing over and over can exhaust the sprouts eventually.
masters degree, horticulture
· 1 decade ago