An infectious pathogen inside California’s pot farms is attacking cannabis plants and growing invisibly for months only to spoil a crop just as a farmer is ready to harvest. Scientists believe that it’s in nearly every pot farm in the state and could be causing billions of dollars in damages to the national weed economy. Hop-latent viroid, or HLVd, shrivels pot plants and reduce how much weight they produce by as much as 30%. It also destroys the amount of THC, pot’s most common active compound, that a plant produces, greatly reducing the value of affected plants. HLVd was first...