Is this plant Bignonia (crossvine)? It would be helpful for everybody if you listed the plant's identification with your images.

Are you watering from a well? If so, is the water being tested on a regular basis? When I had my nursery in SC, I ended up with salty well water, which can really ruin a container nursery in a heart beat. Some of my plants looked very much like yours.

That's about all the insight I can offer at this time, without more info from you. I don't really see anything that jumps out as a disease, to me.

Short of water.
Short of fertilizer.

What's in the potting mix?
Where are the plants growing?
--- city & state?
--- indoors, outdoors, greenhouse?
---- Prevailing temps?

It looks like a palm tree to me.