Watermelon upper stem seems to be dying..

[sniffs]

I have a watermelon growing in a large 5 gallon container.. All the upper leaves on the stem died out real quickly.. I wasn't over watering and haven't been over fertilizing.. It's in a container that has one of those watering trays at the bottom, so I pull the tray off and out came a billion ants. I lift the container up and I see what looks like some mushrooms growing out the bottom... not sure if the ants were feeding on those or the roots but something is killing this plant.

Any thoughts of what might have caused this? It's not totally dead, just it's severely damaged..

https://goo.gl/photos/BcALoZSwC8PmoyW17

[applestar]

For the ants to have been living there, I think the tray is not getting sufficiently flooded and the watermelon dried out. Are you sure those were mushrooms and not the watermelons roots pressed up against the holes? Maybe the plant is already heavily root bound?

[sniffs]

The few "things" I saw coming out the bottom were huge, like half inch diameter and when i tore them, had the same consistency as a mushroom. They didnt look and feel like roots at all.

I ripped the few out I saw and cleaned up the bottom. Good point on the ants tho.. I used a watering gauge and it kept telling me the water 6-8 inches down was "wet" so I never bothered to water it until it soaked the tray.

The pot is one of those larger 16 or 18" 5 gallon pots with the drop tray that has the lip allowing you to water from below(which I never did).. It's possible it's root bound I guess but the plant is so small.. think there's any hope for it?