Yellow leaf with black dots.

[estación seca]

Orchids vary in ease of growth. Dendrobium is a huge genus with plants from many different climates. Different kinds require different care.

This appears to be a Dendrobium from the nigrohirsute group. They tend to be demanding about environmental conditions. They drop leaves and go downhill quickly if growing conditions aren't correct.

What is the name on the tag? What are your growing conditions? Temperatures, humidity, light? How do you decide when to water? How are you watering?

You can look up growing requirements for species at the Internet Orchid Species Photo Encyclopedia, orchidspecies.com. You can look up hybrids at orchidroots.com, which shows the ancestor species. From looking up the ancestors you can estimate growth requirements of hybrids.