Eggplants dying

I have several egg plants looking very unhappy in my garden. The stem about halfway up is brown and when I break it open, it seems to be almost hollow. I can’t find any presence of an insect but I’m wondering if that’s what it is. Or perhaps a fungus? Does anyone have any ideas on what it might be and how to control it. It seems to have hit about half the egg plants in my garden, and the rest are looking hale and hearty at the moment.