Question
Rust spots on underside of leaves.  All flowers have dropped off and none seem to be coming back on.

Answer
Dear Alma, You are located quite far north to be growing a dipladenia and I admire your effort.  Your plant has a fungal infection, and will need to be sprayed with a strong fungicide (something with the active ingredient proprioconozole or chlorothalinol would be ideal).  The main problem, however, is that I suspect your plant is either not getting enough sun, or is not draining well.  If your plant is in a container, then you need to be very sure that the pot drains quickly.  Ideally, when watering, you should be able to saturate the soil, and then the pot will drain without leaving any standing water.  If you have the pot in a saucer to catch overflow, make sure it stays emptied. Dipladenia requires a lot of light, about 6 to 8 hours daily in order to thrive.  So my best advice would be to check your drainage and make improvements as necessary.  Make sure the plant gets plenty of sun, spray with a good fungicide and remove any fallen leaves, and then once the plant starts to perk up, apply a good fertilizer with a higher middle number (ex. 5-10-5) to get the plant blooming again.  I hope this information helps, but feel free to ask me more question.  Good luck.  Melissa