alternatives to pesticides - weeds - blackberry bushes
Although blackberries are native to this region, the species of blackberry that is most invasive is the Himalayan blackberry, an imported species that has naturalized here. It is, however, a source of food and cover for many species of wildlife, not to mention the source of countless jars of blackberry jam. It arrives in your landscape through the help of birds, which introduce seeds in their droppings, or by the invasive roots that creep under fences and out of naturalized areas into your yard. Nothing other than hard labor and natural decomposition will make the canes go away. Furthermore, no herbicide will completely control the roots, so if you use physical methods or chemical methods to control blackberries, continual, persistent removal of the new growth will be necessary for at least a year following your initial efforts.
Encourage the growth of desirable plants, especially vigorous shrubs that will cover the ground, and use mulches wherever possible.
Remove canes by hand and pull as many roots as possible. Wear leather gloves and a long-sleeved shirt and long pants to protect yourself from the thorns. Winter is an especially good time since the heavy clothing will be more comfortable and the leaves will be off the plants, making them a little easier to work through. During the growing season, continue to remove the new canes as they appear. If there are no desirable plants within a foot or two of the cut blackberry canes, pour boiling water on the cut stumps. Also, remember that if a site has been neglected for a very long time, this will be heavy, uncomfortable work. Do yourself a favor and be realistic about how much area you can clear in a day.
Least-toxic chemical control
If chemical control is necessary, paint a systemic herbicide on the leaves while the plant is actively growing. The herbicide will move through the plant to kill the roots.