Suggestions for a systemic insecticide

Through winter I keep half my trees in a bonsai greenhouse, and the less expensive/younger ones in my unheated garage here in northern Vermont. No tropicals among them. Trees in the garage have done just fine by the way for the past 15 years.

The trees that are dropped off at the bonsai nursery are sprayed and prepped professionally before winter sets in. Trees kept in my garage are cleaned up before they are placed inside. Have treated some with a generic insecticide spray containing pyrethrum to kill off aphids late in the summer.

Seeking suggestions for a generic systemic to treat the trees with prior to putting them away for winter. Worried that a spray won’t get at anything residing in the soil. Prefer a product that can be diluted and watered through the soil rather than a spray. Suggestions and sources to purchase from?

Hi @Richard_D
I have to be honest, I have gone right off pesticides. They have their place, and used as a preventative may well be that place. However, I find we (westerners) have a tendency to treat the symptoms and ignore the causes. Plants that get hit by pests are invariably weak and many pesticides are leading to stronger strains of pest.
That being said, I have heard that a dilution if lime sulphur as a wash is effective.