.

you could treat it like a mine, one that already is discovered, so anyone could shoot at the plants. you would also need some stats of course. anything getting into its trigger area gets a template.
back in n2 mines used to have the option of choosing between a circular and the small teardrop template. you could use the circular one only if the small teardrop seem too big.

 

You could use the Hostile Environment rules from N3:
http://wiki.infinitythegame.com/en/Hostile_Environment