I don't believe that the Citrus Blackfly is a pest of petunias nor a pest that would be found in Pennsylvania. Note that these specks are on the upper surface of the foliage, not on the underside, which is where you would find the blackfly (as well as their relatives, the whitefly) nymphs.

Those don't appear to be the nymphs of your blackfly...and you haven't said that you've seen swarms of the adults. That doesn't look like BSM, to me, either. If it were, it would be all over the foliage, as well as the stems.

Do these black specks move? Are they attached to the foliage?

I tell you, these things look just like frass to me. Have you been noticing some caterpillar damage?

No caterpillar damage noticed here.
There was sooty mold all over the Petunias. Some ants also. Very sticky stems and leaves. Aphids?
The Petunia was looking very sickly, then I noticed the ants and sooty mold on everything. My first thought was Aphids, so I sprayed the petunia with safers insecticide soap. Afterwards is when I noticed the black specks, so I have no idea if they were ever alive or not.
I still have the plant and specks.

The little black things look like they could be seeds that fell out of that old seed pod....no?

This was my first year growing Petunias and I never seen there seeds. I'll take a closer look at these black things. Thanks for the suggestion...

first pic..

seed pod... spilt seed????

you sure those arent ripe seed???

ken

Jim, be brave and pick up some of the back things so that you can tell if they are animal or vegetable matter. Or FROM an animal, lol.

OK, never mind...you don't have to. Ken hit the nail on the head! Don't know how I missed the obvious...with the seed pod right there spilling the contents all over the place. Good job, Ken!

Your plants may have had an aphid infestation at one time, or still do. That's what would cause the sticky stuff.

Look at the FIRST picuture on this Google images page.

Here is a link that might be useful: petunia seed pod and seeds

petunias are naturally sticky ... arent they ...

patty nailed it also ... but her reply was not there when i typed mine.. though it is here this morning .... GW gets weird sometimes ... no matter how many times i hit my browser refresh ... whats that all about??

jim .. petunia get SPENT ... they start looking ratty ... a severe pruning.. or cutting back MIGHT get them to recuperate ... but one thing for sure.. with annuals [in your zone] ... most will stop blooming profusely.. once seed is matured.. their job is kinda done ...

you will have to learn about deadheading.. if you wish to extend the flowering season longer ...

its hard to explain based on your pix.. but you might trace back a large branch.. back towards the main stem.. looking for little buds.. and then whack off most of the side branch.. hoping to stimulate the last 2 or 3 buds ... in a prefect world.. those would start growing.. and inside a few weeks.. you might get a new series of flowers ... [or they just might die.. since they already spread their seed]

if the plants have many branches... say 6.. clip two as i suggest ... and see how they respond... if you start to see new growth.. then clip the rest..

you have a multitude of plants.. experiment...

ken

Yes, Patty had her eyes open, too! When I look at the first picture with the seed pod smack in the middle...dumping a pile of seeds all over the place....I have to laugh at me. Caterpillar poop!

I can't remember if Petunias naturally sticky or not. I stopped growing them years ago because I was tired of all the deadheading involved and those summer 'blahs'. I do like the calibrachoa, but that's as close as I'll get.

Are they sticky?

Ok, here's the deal. I took samples to our local Agri office. The Petunia had botrytis blight. It did not have sooty mold. Botrytis blight caused the leaves to drop fast exposing the stems to intense direct sunlight all day.
And those are Petunia seeds. lol. Thanks Everyone for your comments.

Hey, thanks for getting back to us! Also, thank you for sending us such good images. You wouldn't believe some of the pictures we get, lol. Yours were terrific.