I would recommend you avoid them all. There are no 'safe' herbicides to use around trees. Most of them are neonicitnoids and will kill a lot good insects as well as the plants. some of them have been shown to kill trees.

Hand pulling or smothering the weeds are your best bet. 

Systemic herbicides kill plants by moving through their circulatory systems. Lower concentrations only mean that they will kill more broadleaf (read trees here) plants and not grasses. this is only because thin grass blades take up less poison.

Spray weeds also means drift. Even with little to no wind, you will have drift. Some of the chemicals have been shown to drift later. Spraying in temps over 80° can cause them to atomize.

If you choose to use an herbicide, the article below should help you understand the risks.

https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=24291

You may find this article interesting. 

https://mitppc.umn.edu/sites/mitppc.umn.edu/files/2024-06/Guide-to-forest-understory-revegetation-buckthorn-2024_3.pdf