"Getting into the weeds"

I heard the phrase this afternoon on an NPR radio program about recent Congressional shenanigans and had to look it up.  The best I could find was a column in The Word Detective from 2011, excerpted herewith:

“[I]nto the weeds” now seems to be very, very popular, to the point where it earned its own article in the Christian Science Monitor in 2008. That article, in turn, heavily relied on an immensely helpful 2006 post on the excellent linguistics blog Language Log by Mark Liberman, who did some solid research on the phrase.

There seem to be two different uses of “getting into the weeds” out there in the wild. One is the “getting into too much (possibly irrelevant) detail” sense that you mention. This is evidently a very popular figure of speech among policy wonks, beltway insiders in Washington, D.C., and savvy observers such as Talking Points Memo’s Josh Marshall, who has frequently used the phrase in his articles. The other sense is a restaurant term invoked when the staff is overworked, everything is going wrong, and total chaos is only a burnt fillet of sole away. Back in 2000 there was actually a Molly Ringwald movie about the staff of a restaurant dealing with a bad night called “In the Weeds.”

Golf, rather than farming, is favored for the etymology (details at the link).