Several here have already spoken the facts-that the stuff on the tree is all harmless, but that still, it's not good to see so strong a showing on such a dinky plant already...and that the general aspect of the tree is not good. BTW, in florida, there is a bright red-orange lichen-also harmless-but most unusual to see. Looks like a bit of that is starting here too. And also BTW, even very flat white patches on trunks is usually also a lichen, one which has not yet had its photosynthetic algal partner kick in yet. One more thing-the stuff that is more spiny looking is probably a Tillandsia, an epyphyte or "air plant" which also is common in FL, also harmless, and is a Bromeliad. You initially said "fungus" and the lichens are paramutualistic organisms, one part of which is a fungus. But again, it is not only not harmful to whatever tree it may be growing on, they' re of great interest and beauty. +oM

Fungal spores can overwinter on twigs and branches on the tree and on any fallen leaves that have not been removed. The only way to effectively treat scab is to spray before symptoms occur and again, as conditions warrant, periodically into the growing season. Best to alternate between two different fungicides as the organisms have an ability to adapt and build resistance against a single type. The rust is harder to control as it requires removal of the host species (a juniper) which may or may not be located in your garden. But its damage tends to be more cosmetic although just as unsightly. You will never be able to predict when or if these diseases will occur.....these things are just beyond our control. There is no point in doing anything at this time as nearly all fungicides are preventative in method, not curative, and it is too late to have any effect. Personally, I am in that camp that says this is just wasted effort on something as egregious as an ornamental pear tree..........removal is your most desirable option :-) There are so many more beautiful flowering trees one could substitute for the smelly, invasive and structurally weak and disease prone Callery pear.

That looks like wilt damage from getting too dry or sunburn from too much light too fast. Your tree will grow new leaves and be fine.

plum pockets disorder? Caused by a fungus. I am no expert on this fungal disease (if that is what it is). Sounds like what you have however. I would be real worried about it spreading to your other plums. I recall NY had a major outbreak of it a few years ago and some counties were quarrantied to prevent it from spreading. Lots of info on the web about plum pockets.