I need to bring in my potted lemon tree before the temps. get too cold. There are probably ants in the pot's soil. Is there a recommended treatment for this issue? The tree is a bit too large to repot so I am hoping there is another solution. Thank you!
Check the soil for ants and look for scale insects on the foliage and/or stems https://ask.extension.org/expert/questions/433856.
Drench the soil with water (you should see ants if they are nesting). Wash off insect pests or apply a labeled houseplant insecticide to control any plant pests such as scales. Once you bring the plant inside you can place outdoor ant bait stations on the soil of the pot if you have an ant issue.
Here are more houseplant tips http://extension.umd.edu/hgic/fall-houseplant-tips