Ask Mr. Smarty Plants

Since this plant is not native to North America, it is obviously out of our area of expertise, and we have no information on it. However, it can be easily disliked by us anyway.

From the Plant Conservation Alliance's Alien Plant Working Group LEAST WANTED Japanese Barberry. We don't think we could say a single thing that would make our feelings any more clear than what is said in this article. From that site:

"Japanese barberry has been reported to be invasive in twenty states and the District of Columbia. Due to its ornamental interest, barberry is still widely propagated and sold by nurseries for landscaping purposes in many parts of the U.S."

"Japanese barberry was introduced to the U.S. and New England as an ornamental plant in 1875 in the form of seeds sent from Russia to the Arnold Arboretum in Boston, Massachusetts. Japanese barberry spreads by seed and by vegetative expansion. Barberry produces large numbers of seeds which have a high germination rate, estimated as high as 90%. Barberry seed is transported to new locations with the help of birds (e.g., turkey and ruffed grouse) and small mammals which eat it. Birds frequently disperse seed while perched on powerlines or on trees at forest edges. Vegetative spread is through branches touching the ground that can root to form new plants and root fragments remaining in the soil that can sprout to form new plants."

When you scroll down that page, you will find excellent Management advice, but it is not going to be easy. We urge you not to use sprays as they can disperse to harm more desirable plants, even animals, like people. The first thing we recommend you get is a long-handled pruner, with very healthy cutting edges. When we say long-handled, we mean one that you can stand erect and use, as your back is going to be in enough pain as it is, and you sure want to stay away from those thorns. As the referenced article points out, you want to prevent it from seeding out however you can, all year round. Cut off the seeding heads and dispose of them where they won't be available to birds for dispersal, nor can be washed onto new ground by rain. Again, that long handled cutter will come in handy.

Now, to get at the root of the matter (pun intended.) Starting from the outer edges of the infestation and using the pruner, cut a plant's root off as close to the ground as possible. Immediately, using a long-handled sponge disposable paintbrush, paint that cut root with an undiluted wide-spectrum herbicide. You need to do this quickly because that cut area is attempting to heal over to protect the very root you are trying to kill. Do this with every branch or trunk that sticks itself out of the ground, as well as branches touching the ground because the plant can sprout from those, too.