Should I include reference section on a conference poster?
Biologist here. 

I tend to be more careful to cite methodology on a poster rather than things that belong in an introduction or discussion section, and especially anything derived directly from a particular paper, such as an equation that is on the poster.

Sometimes there is a particular key reference - either a review or highly relevant original paper - to cite for background. Otherwise, if you find yourself citing a lot of things you probably have too much text on the poster.

(to be clear: if it needs to be cited, it should be cited; it just turns out that the type of content that needs to be cited should be at a minimum on a poster)