They also have a significantly different thermal signature (pot is very hot as it grows) so they stand out quite nicely when viewed through thermal imagers. You also can't hide the signature without obviously hiding the signature. That is, any effort to hide the pot signature looks like someone is trying to hide something which could be enough cause for suspicion for a warrant anyway.
Obviously these were drug pushers and not just recreational users growing their own. Bust them and throw away the key. (or perhaps burn them along with their crop. I'm easy)
I guess the big distributors of alcohol like Budwesier and Miller are big drug pushers, too. Should their factories be burned to the ground with all their employees, too? They're the biggest, most destructive, drug pushers around you know.