Ask-a-Dave's-Gardener: Bug-infested Blue Sea Holly - HELP!, 2 by valal

valal wrote:
I have been working on a large garden project since last June. This year, among other things, I put in Blue Sea Holly..my first time at growing this. I lost a couple I think I overwatered? They did better in the ground, but 2 of 3 died back anyway. Yesterday I noticed the one is doing well and seemed to be getting ready to flower ..so was excited. Was out taking photos tonight and saw a bunch of black stuff on the stem. We had a ton of heavy rain, I thought it was dirt but alas, I have a terrible back bug problem....Not sure what they are (I'm a newbie that fortunately hasnt had to deal with alot of pests yet)

What are they? Can you tell me how to get rid of them?

THANKS in advance!