I notice that there are some strange foam on my plant as if someone has been spitting on it. Is this spittlebug or are there other beneficial bugs that generates foam?
Spittlebugs are the only creatures that I know of. Unless you have a serious number of them, I'd not worry about it. If just one plant is affected, you can spray the globs with water from a hose to knock the nymphs off. Insecticidal soap can help with these guys, too.
Paul, this is a year I've seen a lot perennials with spittle on them. I don't do anything and it hasn't seemed to affect anything negatively.