Tropicals & Tender Perennials: New lesson/leaf damage, 0 by Calalily

Calalily wrote:
Snails are a constant problem. I put out bait, they eat it and more take their place. These leaves were against the side of the gh, where it's moist and snails love moist, shady conditions. Here is the next symptom that is manifested by leaf yellowing. What caused this? Is it a disease? Cultural problem? There are lots of these yellow leaves, only on one plant, older leaves only. No apparent insect problems. What did I do to this plant? I know, do you?