lily, one of the most common issues with pachysandra in your area is volutella blight - begins as tiny tan or brown spots that eventually merge together and kill an entire leaf.

Does your problem look anything like this?

Here is a link that might be useful: Volutella blight

how about just posting a picture ...

never heard of surface application of diatam. earth in teh heat of summer ....

nor late summer oiling ...

i would start with asking what kind of tree ...

how long have they been there ....

how do you water them ...

do you fert ...

are they near a lawn that is sprayed ...

etc ....

post a pic if you want to get anywhere with this. i doubt we can do much for you w/o such .. check out the link ...

ken

Here is a link that might be useful: link

to morz 8 saw that picture today. sure looks like my problem-a biiig one.
diam.earth:Diatomaceous Earth kills aphids, white flies, beetles, loopers, mites, snails, slugs, leaf hoppers, and harmful pests.
neem oil i used to manage fungus, neem is very effective at smothering insect eggs and soft-bodied pests such as aphids, mites and white flies.
what tree???

Lily, a thorough clean up of any leaves or debris, thinning the plants if necessary to increase air circulation, avoiding watering in later afternoon or evening so plants aren't spending a night wet...may help if its really volutella.