In order to inject the Termidor SC liquid into the beams you will need to drill holes every couple of inches and use a sprayer with a pinpoint stream or a straw attachment to get the application into the holes. Another option would be to use Termidor Foam which comes in a ready to use can with the small attachments to get the foam into the drilled holes. Using a needle and syringe may not offer enough product and pressure into the areas for best coverage.