Could be little black aphids. They like to congregate on stalks. Squirt them off with a spray of water either from a hose (don't destroy your stems/stalks) or squirt bottle- simple as that. Which reminds me, I have a crop of them that need attention right now.

Here is a link that might be useful: {{gwi:645159}}

I once had such a congregation on one of my lupins - I was so disgusted I cut the stalk off - but it had already bloomed anyway. I did not know at the time that aphids came in different colors - even red I think. Yes, apparently just spraying them off with a blast of water does the trick.

Anna