You should repost over onthe discussions page.

It probably needs to be repotted. Miltoniopsis should be repotted yearly for best results. They don't usually tolerate the salt buildup in media that is over a year old.

Miltoniopsis is one of the most difficult orchids to grow. It seems to be more than usually susceptible to bacterial/ fungal disease and yours may already be too late to save unfortunately. Try the following:

How to save a dying orchid

The commonest cause of premature death in cultivated orchids is bacterial and/or fungal rot. I have been able to save about 30% of very sick plants by this method.

1. If the plant is in a pot remove it entirely and wash off all the compost. Either heat sterilize or discard the remaining compost.
2. Using a sterilized knife or secateurs cut away all the dead root, even if this means leaving no root at all.
3. Prepare a solution of onion tea by cutting a large onion into large pieces and simmer in 1-2 pints of pure water for about half an hour. Allow to cool.
4. Immerse the entire plant in the solution for about half an hour.
5. Wrap any remaining root in damp sphagnum moss and place inside a clear plastic bag then seal.
6. Place the bag with the plant in a warm, well shaded place and leave for about 4-6 weeks.
7. After this time inspect the bag without opening it if possible. If the plant appears to have deteriorated further, discard it. If it is showing signs of regrowth remove and place in sterile compost then grow as normal but keeping fully shaded for a at least a further month. If the plant has not deteriorated further but is still not showing signs of regrowth leave it in the bag for a further month. Repeat.
8. Plants grown in baskets or on plaques may also be treated by this method. In this case miss out step1 and soak the whole mount in solution. Plants grown by this method are less prone to disease than those grown in pots.
Prevention

The onion tea method can be used as a simple preventative as an alternative to using commercial products, Simply mix the tea with about a gallon of pure water and soak the plants as normal.

Heat sterilization

Heat sterilization is an essential procedure to prevent the introduction or spread of disease. Any cutting tools should be sterilized by heating in a flame before use. Small quantities of compost can be sterilized by placing in an open container or pot and heating in the microwave for 2-4 minutes depending on the amount. Always dampen the compost first. Dry compost can catch fire! Large quantities of compost can be sterilized by putting inside a wire mesh basket and placing on top of a smoky bonfire for up to half an hour. Once again make sure the compost is damp.

Good luck!

Ian Fraser (Nonsmokinjoe)

Let me hold up my hand and admit error. I read your post without really looking closely at the photograph. On reflection I think it is quite possible you plant is perfectly healthy! All orchids (all plants) shed old leaves from time to time. If the new growth appears healthy I would do nothing, but do take strong precautions against bacterial/ fungal disease as suggested.