We don’t have the weather to grow most of those fruits. While the climate is ok for watermelon, can’t grow those either. Some soil borne disease is what I’m thinking.
To grow watermelons I take a 1 cubit foot bag of mixed manure and a 1 cubit foot of cheap topsoil.from the garden store and mix them and then dump the mixture on top of the ground. I don’t even mix it in the soil. I then lay out cardboard about ten or twelve feet around the pile of soil to prevent weeds.
Doing this means I don’t really till down. In places I only have 1/2 an inch soil before I hit coral limestone.
It may be a soil issue but it may also be snails, slugs and beetles eating the shoots.
Fusarium wilt I'm bettin'. It's murder on all melons.
They finally have some varieties with decent resistance to it.