Damaged Pinto Bean Plants

Hi, l’m hoping someone can help me diagnose the problem with my pinto bean plants. This is my first time growing plants outdoors, so I’m still learning—I planted around 300 different plants all over my front-yard, back-yard and in all the pots I could find, so I’m hoping to learn as quickly as possible as I don’t want them all to die.

These eroded-looking areas appeared over just 24 hours. It was about 80 degrees out yesterday, so I’m thinking maybe it’s related to that(?), but the instructions on the back of the seeds said to keep them in full sun exposure. I also considered bugs, but I can’t find any anywhere on/around the plants. Should I cover them with some sort of mesh? I don’t know what to do here 😅 Please help