I have quite a few lilies, but I planted 6 along the edge of a recently manured fallow spot because the lilies were extras. They came up this spring, and grew to a good height and then 3 of them began turning yellow. I pushed them gently and they fell over revealing hollowed out stems at ground level. Does anyone know what this might be from? Note that the spots on the leaves are from Asian lily beetle. I think I was on top of them, and they are probably not to blame.

I see in the preview that the resolution of these images has deteriorated. I guess that's from saving them and then retrieving them and posting again. The insides of the stems were brown and cleanly hollowed out at the point where the stem broke.

TIA
LAS

Have you tried digging up one of the bulbs and seeing what condition it is in? For example, are the scales falling away from the base of the bulb or is the bulb nice and firm?

Or it could be a borer.

Pardalinum, I will dig up when I return to our summer place and report.

Magnolialover, what kind of borers attack lilies?

TIA
LAS

corn borer has damaged mine in the past. It hollows out a section of the stem and before you know it the stalk is wilting over.