Be careful using Roundup! It can most definitely affect a tree in a pot when it’s applied to weeds in the pot. It might not kill the tree, but it can cause deformation of the foliage, and the tree will look “sick”. Curled needles and foliage.
A former apprentice at Boon’s applied Roundup, using a paint brush on just the weeds in the pots of many bonsai. Layer, the trees had curled and deformed leaves. For a while, it was thought there was a mite that infested the garden, but later, it was determined that it was the Roundup. Boon didn’t know the apprentice had applied the Roundup until later. He discovered that the apprentice was doing it without his, Boon’s, knowledge. Once the Roundup “treatments” stopped, the affected trees resumed growing normally.
Two of my trees were affected. They have both fully recovered, but it was scary for a while!