124 light years seems quite close, it seems to be some sort phytoplankton for now, what can we send there quickly to eradicate them before they become a problem

124 light years seems quite close, it seems to be some sort phytoplankton for now, what can we send there quickly to eradicate them before they become a problem. How much mass of galactic "roundup" should we send ? Do we have the technology yet for planet-scale sanitizing ? Can we pulse some high energy particles at roughly the speed of light and aim it at them ? Do we know if they have some magnetic field protection like earth does ?