Soil Treatment for lemon trees

I have had my Lemon Tree and Lime Bush outside for the summer (Wisconsin). I usually use a treatment in my plants soil before bringing them inside for the winter (to kill unwanted bugs). I am not sure what I should use for these plants. We use the fruit from them and want to be sure that whatever I use is not harmful to humans. Thanks for your help

 

Horticultural Oil spray will kill most any bugs--aphids, scale, mites--and it is totally non-toxic.