How to Stop Boogering?

I'm getting a lot of boogers on my prints. I have been manually cleaning them, but sometimes miss and the extruder will hit a hardened booger and cause the extruder or bed to jump a tooth (see pic).

I've been experimenting with slic3r configs, varying the Retraction (0.2, 0.4, 0.8, 1.0) but still getting them (my Retraction is set at 0.4mm, Speed at 20 mm/s).

I also set Seam Position to Random, which may exacerbate the problem as it tends to make boogers when it moves from one start location to another. I'll try changing this to Nearest, but prefer not to have the seam.

Should I be adjusting something else or should these settings be different?

Thank you!

 

Before these prints I changed the Z axis lift under Retraction settings to 0.2mm (from 0), I'm wondering if the lift is what is creating the wisps of filament that turn into boogers. I'll try switching back to 0 and see if that helps.