NoID with two toned leaves- what’s wrong?
 

The leaves are two toned, this just started about 2 weeks ago. I grow indoors, water weekly and fertilize biweekly. Bright light temps in Home in 72-78 range.

Any chance it's a light sunburn? Does it get direct sunlight any point during the day?

Also looks like a nutrient deficiency but those don't tend to "suddenly" appear.

Is it deciduous? Mine discolors just before dropping leaves.

No direct sunlight. This is the new growth after flowering

---------- Post added at 07:07 PM ---------- Previous post was at 07:05 PM ----------

I have no idea, this is the growth after it blomed. It was all green when it was smaller, then started with the light area on the leaves and has not gotten any larger.

The plant is a Dendrobium phalaenopsis type, also known as a Den phal. The leaf damage looks like spider mites. You need to move quickly.

Spider mites are eight-legged arthropods so small they're hard to see. They suck plant juices, usually on the undersurface of the leaf. They spin a very fine web on the undersurface that gives the leaves a silvery appearance. As the infestation progresses they envelop the plant in the fine webbing. They can kill a plant rapidly. They love warm, arid weather. High humidity and cool weather often keeps them in check. They are commoner indoors where air conditioning and heating lower humidity. Some plants are more susceptible than others, and Den phals are quite susceptible.

Take a tissue and wipe the undersurfaces of the leaves. If you see brownish or reddish streaks, you definitely have spider mites. Your plant looks so certain for mites, though, that I would treat for them even if you don't find the streaks.

Mites develop resistance to chemical pesticides rapidly. They are naturalized in your region so you won't be able to get rid of them permanently, just control them. I spray rubbing alcohol straight from the bottle (the 70% sold in drug stores) or a solution of 1 quart / liter of water with 1 teaspoon / 5ml liquid dish soap. I make sure I wet the entire surface of the entire plant.

This kills adults but not eggs. You need to retreat for another 2-3 sprays at 3-5 day intervals. The warmer it is the faster they complete their life cycle.

Then you have to be on the lookout. A sturdy spray of water usually does the trick. Once a week or so take the plant to the sink or shower and spray down the leaves with water. This will knock off mites.

Thanks! I will isolate it and treat it! It has been close to a cattleya, should I treat this one as well. It looks fine. No leave damage.

If you find mites on the Dendrobium, treat all your plants. The mites can be there but not be causing much damage.

The leaves are discolored for several reasons; what did estación seca or MrHappyRotter or AnonYMouse say. I add another reason; the pot is too big, the roots are destroyed and the plant, to survive, pulls the food from the leaves. The leaves will fall and in the spring when a new vegetative season begins, new cane will grow. Do not abuse with water, wait until the plant enters in vegetative stage and transfer it to a small pot (half of what is present).