You Could Look It Up

Q. I am editing a short-story anthology. One of the submissions contains this phrase: “barb wire fence.” My instinct tells me that a hyphen is needed between the first two words, yet I cannot locate an example from a reliable source. What do you recommend, please?

A. Merriam-Webster.com lists barbwire as one word. (Barbed wire is the main entry there; barbed-wire fence is an alternative to barbwire fence.)