I'm an enthusiastic Datura gardener, Spider-mites live on the underside of the leaves, cutting away the populated areas won't do the trick. I have ALWAYS used NEEMS OIL as a VERY effective insecticide/fungicide/miticide. Your local LOWE'S store should have NEEMS OIL in their gardening center, or a NEEMS Concentrate. It's good for the plants and stops whatever insect is feeding on your plant by eliminating the insects ability to eat AND molt (molting is when the insect changes per se from larvae to pupa to adult...) The stuff works WONDERS! It's important though to mix the NEEMS with warm water (not below 45 degrees Farenheit) and add a dash of dish soap to it to help it mix with the water. Spray the WHOLE plant, especially the undersides of the leaves, and do it again in 4-5 days until no bugs. It's best to continue using NEEMS on a regular basis every 14 days or so, but that's just a recommendation.

--OH! Also with your Daturas, NEVER use organic fertilizers. Daturas are prone to fungal problems in their roots, organic fertilizers have been known to bring in bacteria that chemical fertilizers wouldn't. Just letting ya know cuz it sucks to lose a BEAUTIFUL plant due to a virus that could of been avoided.

HOPE THIS HELPS!!!!