Dendrobium Leaves Yellowing and Have Texture

[estación seca]

Welcome to the Orchid Board.

First, the roots look OK to me. The picture isn't great on my phone.

Thin-leafed Dens are prone to spider mite attack. It can look exactly like this. I think that is the likely cause. Use the Search function above to read about spider mites.

For now mix a solution of 1/2-1 teaspoon of liquid dish detergent per quart of water. Spray all surfaces of this, and all your plants, because spider mites are likely present even if not causing damage. Spider mites always come back so you need to watch carefully and be prepared.