The hollow stems may be from a stalk borer. It's not a significant threat on established plants, but it can be quite annoying. There's no really good control -- some people slice out the hollowed part and try to catch the caterpillar, but destruction of nearby weeds is probably more effective. Sprays won't do anything.

If the fruit that is wrinkling and turning mushy isn't on the wilting stems, there may be a problem with inconsistent water. It can cause shriveling as well as splitting and blossom-end rot, and the end result is generally mealy and tasteless. I'm assuming that the fruit is otherwise edible... mulching well may take care of that, and watering a bit more often.

--Alison