Indoor maidenhair fern - white substance at the bottom of dead stems, mealybug residue?

[Sweets777]

I've attached pictures of the base of some dead maidenhair fern stems that I've clipped from the plant, but most dead stems have this to some extent.

I haven't seen any active mealybugs, but does this look like their residue? If mealybugs are the culprit, it seems like they must be dormant within the soil and I suppose I'll have to do a root soak in neem oil.