I would fill the crack with glue, then wrap sinew around the knot... 1-2 layers going with the length of the bow, then 1-2 layers wrapped around the stave. this should hold the stave together. Another trick is when tillering the bow, keep this area a little stiff and tiller more above and below the knot. It will still shoot but it will releive a lot of stress on that area and your bow should stay together.
good luck