Missing leaves - another form of "skeletonized"
Section by section, leaves on my four-year old scarlet runner bean plant completely disappeared. Pod production had begun. No debris or worm droppings on the ground. I clipped off the affected branches but that did not prevent the spread.
(Side question - how many years can scarlet runner bean plants last?)
In Nov. I planted fava beans to winter over in a nearby bed and the same thing happened when they were a couple of feet tall. All the healthy leaves were gone within a week. Some new leaves are growing back now as the days are getting longer.
Scarlet runner bean (Phaseolus coccineus) plant is a perennial vine, but commonly treated as annual plants.
I suspect the culprit could be slugs. They generally feed during night. Try to look out for slugs during the night and hand pick them or you can use beer or milk traps.
How to prepare traps- Take any wide mouth plastic container and quarter fill with either milk or beer, and buried the container by digging a hole and leave approximately 1/4 " above soil. The slugs will fall and die inside the container. Change the liquid two or three days once.