Hey David, there are different bowings that fit different styles of fiddle music. A very common bowing is when you slur two eighth notes together, and then play two eighth notes separate. This is very common in 2/4 and 4/4 time. Another common bowing which I wrote about in my book is called the Georgia Shuffle. This is a little more complicated but is common in fiddle playing.
You don’t have to rely on doing one specific bowing pattern. Many times a fiddler will do the Nashville Shuffle bowing the first time, random bowing the second time, and Georgia the third time. Fiddle playing is a lot more loose compared to reading traditional classical music (where you stick to what is on the page).
So a simple answer is–slur whenever and do things similar to Nashville and Georgia bow patterns.