Bush bean problems

[adamra1]

I planted these bush bean seeds about 3 weeks ago and they were coming up nicely until a few days ago when they started turning yellow and the edges of the leaves are brown and mushy. Its strange because its only happening on about 1/2 of the bean plants. Is it the amount of water they are getting or a nutrient issue?

[imafan26]

Definitely an overwatering problem. the stem coming out of the ground does not look healthy.

[jal_ut]

Hmmmm........ I'd be looking for some insects. Maybe cutworms? Check carefully on the underside of leaves for small insects.