I've had gardens for 30 yrs and never had a decent watermelon . My daughter grew 1 perfect , delicious one in her first attempt. #dadisacrappygardener.
Bugs possibly but most likely wet ground. got to elevate them off the ground unless you have a slight grade. Old plates upside down are good. I have used plastic crates also (upside down. This year I am trying out some oil changing plastic tubs. If I can get them on sale I will use upside down Lugs, like what a butcher users. I want the melon to never sit in water or dirt.