The thing that kills Japanese barberries best is a foliar spray of triclopyr applied when the leaves are out. This single herbicide for barberry treatment hits 93% kill rate in field tests. No other method comes close to that number on its own. If you want the plant dead and gone, triclopyr on the leaves during the growing season is your strongest option.
I've used several barberry treatment methods over the years and the gap between them is huge. Pulling small seedlings by hand takes me about 30 seconds each and works great. But walking up to a mature colony with stems as thick as your thumb is a whole different fight. Those old plants have deep root systems that snap when you pull. Any root piece left behind can send up new shoots the next spring.
Penn State Extension puts out the best herbicide for barberry guide I've found. They suggest mixing glyphosate and triclopyr at a 2:1 ratio for the top kill rate. You spray this mix on the leaves during summer when the plant is growing fast. The leaves need to be fully open so they absorb the maximum amount of chemical. Hit every leaf surface you can reach and come back in two weeks to check for any green shoots you missed.
If you don't want to use chemicals, your barberry treatment methods narrow down but still work. Hand pulling gets rid of seedlings and young plants with thin stems. Use a mattock or weed wrench to pop out larger root balls. Cutting the stems to ground level and then burning the stumps achieves close to 90% cover reduction in test plots. This cut-and-burn combo works much better than either step alone.
Flame weeding by itself sounds appealing but the numbers tell a different story. A propane torch on standing barberry never tops 40% kill rate in any study I've read. The stems char on the outside but the roots stay alive under ground. The plant comes back from the base within a few months. You can use fire as part of your plan but don't count on it as your only tool against an established patch.
Here's the part most people skip and it costs them. Barberry seeds stay viable in the soil for up to 9 years after you kill the parent plant. That means new seedlings can pop up for almost a decade even after you've cleared every bush in sight. Mark your calendar to walk your cleared area every spring for at least 3 years and pull any new sprouts you find. This follow-up work is just as vital as the first round of removal.
Start your plan by matching your method to the size of your problem. A few young plants in your garden bed need nothing more than a shovel and some elbow grease. A thick hedge or wild patch calls for the herbicide approach or the cut-and-burn combo. Large forest areas may need help from a land management crew who can cover more ground. Whatever method you choose, commit to the follow-up checks or your work won't last.
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