I'd take a sample to your local office of your Rutgers Cooperative Extension Service for identification and any treatment suggestions.

Here is a link that might be useful: Rutgers CES

i would call it a bug...

and considering all the leaves will be falling off in a month or two.. i would ignore such ...

those leaves.. even as they are.. are functioning on the plant.. but for you taking them off ...

plagues of bugs come and go over the years... you need not presume ever one that comes along.. must be slaughtered ...

as a newb.. my biggest suggestion is to ignore such ...

a given plague.. can even completely defoliate a tree.. and the tree will releaf and move on with life ...

learning what it is ... is knowledge. and knowledge is power ..

but please... unless you see that the tree is dying ... dont go bat carp crazy spraying all kinds of things onto it ... for a transitory problem ...

full fall cleanup never hurts.. to make sure you dont encourage it into next season ...

ken

Thanks for the replies. A follow up based on those.
One, I don't remember seeing any pear slugs (I googled for their images). And this is on *almost all* the leaves of the two trees.
Secondly, I have attached another picture. Notice the black spots. It is on those spots that the leaf disintegrates. I am fairly certain that this problem is still occurring because I am tracking a few leaves and they have progressed from black spots to holes over the last few days.
Given this information, what is the prognosis ?
Thanks again for the help.

Hi

I was wondering if there were some further hints as to what was causing problems. Are these black spots indicative of the slugs ?

What care should I take for next year when the leaves come back. I am presuming this year is a goner. Can I do something that will help me next year ?

Thanks for the help
vk

Hi it is definitely a pest. Some type flying insect like japanese beetles or butterfly caterpillars. I have a lot of japanese beetles that land on mine in the warm part of days and damage them. Butterflies like laying their larvae in them too. They eat my roses and too.

I am surprised that on this 10 year old thread, no one has yet offered the correct answer to the OP's question. That assumes the theory that none of the responders actually grow this tree. It is NOT a pest or insect issue. It is leaf spot disease (aka "shot hole" disease), which can have either a fungal or bacterial origin. It is very common on Prunus species, of which purple leaf plums are one. They are extremely prone to this issue.

There are scores of publications online outlining how to treat this issue although the situation is really more cosmetic than actually harmful to the tree.

I love how brand new members feel the need to sign on to an outdated thread just to make a single post that continues to provide incorrect info!! Really??