Mottling and yellow tips on oncidium. Disease, nutrition or...?

[estación seca]

It might not be getting enough magnesium. I think these do better with more fertilizer than 100ppm once a week. Consider treating with Epsom salts on a different day than you fertilize. A tablespoon per gallon of water should work. It can take weeks to resolve magnesium deficiency.

I don't worry about algae nor cyanobacteria.

9 hours of light daily probably isn't enough, unless they also get natural light. That isn't causing the yellowing but you might have trouble getting them to flower. Many people use 12 hours spring/summer/fall and 10-12 hours in winter.

[sunfire]

Thanks. I will increase the magnesium.

Originally Posted by estación seca

It might not be getting enough magnesium. I think these do better with more fertilizer than 100ppm once a week. Consider treating with Epsom salts on a different day than you fertilize. A tablespoon per gallon of water should work. It can take weeks to resolve magnesium deficiency.

I don't worry about algae nor cyanobacteria.

9 hours of light daily probably isn't enough, unless they also get natural light. That isn't causing the yellowing but you might have trouble getting them to flower. Many people use 12 hours spring/summer/fall and 10-12 hours in winter.