Question

trunk   We have 2 red maples that we planted about 3 years ago. They have never really thrived, thought they were planted in good soil and were kept well watered until we went out of town for 3 months, from August to October, which is a very hot time in FL.  When I returned I noticed that the bark was cracked open on one tree.  When I investigated further, I noticed mottled gray and brown patches and lichens on the trunks. Have they been lethally attacked by fungi while they were in a state of dehydration perhaps?  Can they be saved?

Answer
I do not think there  is a major problem. As a maple grows thre bark will go from smooth to fissured or cracked. I think that is what you're  mainly seeing. The lichens are not a real problem on healthy trees. I would fertilizer the trees with 10-10-10 fertilizer at the rate  of 1  lb per inch of trunk diameter. I would lay off the water an dangly water if it does not rain for a couple of weeks.