jade plant dieing
I have a number of jade plants from an original that is greater than 30 years old (they even flower!) The originals have stems that are >6" diameter. I tend to fight mealybugs most winters and have been challenged with mealybugs on 2 of them this year. The first died--either from too much horticultural oil (not my first choice of insecticides) or it got too cold when I left it in the garage one night after treating it. The other is dieing from something I have never seen before (mealybugs not quite gone)--it is getting dark brown spots that start anywhere but more frequently near the attachment of the leaf to the stem and spread over the whole leaf, then the leaf dries up and is covered with a lot of clear, dry material (that is so light and thin, that you can't feel it) that sticks to the leaf and drops off it. Many of the leaves, but not all are yellowing before the brown spots start. I have treated the plant this winter with orthene, then diazinon, then horticultural oil. Are you able to tell me what is wrong with it and if there is anything I can do to save it.
Sounds like a root problem or it could be a cumulative response to the mealybugs, which do inject a toxic saliva.
We recommend that you cut it back severely. They can tolerate this and regrow. The new foliage should be clean of mealybugs. You'll also need to repot it because the mealybugs get in the soil. While repotting, look for root rot, too. Of course, keep this infected plant far from your healthy ones.
You also may want to send us photos of the plant, close up as well as full shots.