So it is time to do the wood filler trick. I do not buy retail wood filler, I make my own.
This time I used a combo of Titebond liquid hide glue and some sanding dust from the filter bag on my excellent Ridgid random orbital sander with variable speed.
Stir it together to form a thick paste and use a small spatula to force it into the cracks. Here is what the filler kit looks like. I keep vials of dust from a variety of wood species and use various glues to make the paste, from Weldbond to hide glue to epoxies, depending on circumstances and what effect I am looking for. This time I want the filler to show as a dark line.
Next trick is to show you how I sand the rungs.