mrsross I don't know what it is but there is something wrong. It may be very minor or may get worse. I have a lot of melon plants both short vining and standard and none of them have any yellow leaves or dead leaves.

A short list of what can cause your problem. (I'm sure there are more.)

Have you stepped on any of the vines or leaf stems?

Have you watered in the late afternoon and sprayed water on the leaves?

Have spilled fertilizer on the leaves or stems?

Have to inspected for insects and powdery mildew?

Are they getting to much or to little water?

Are they getting enough hours of direct sunlight? (At least 8hrs.)

i have sprayed water on the leaves...i shouldn't do that? watering is in the morning, but there have been a couple of times where i thought they may need more and watered in the afternoon...they have a lot of hours of direct sunlight, but i do have a shade up...should i take it down? its a 60% tan shade.

Melons do not need shade. They thrive in full sun. In El Centro California it hotter than it is here and they grow melons in fields with no shade all summer long. A soaker hose is a better way to water because it does not get the leaves wet and water does not splash from the ground onto the leaves. If at all possible try not to water too late in the afternoon. It takes a longer for the moisture to dry up and molds and fungus's can form which damage leaves and crops.

with 60 percent shade cloth they may need to be hardened off again. On a weekend soon try this. Given them an extra 4hrs of sun on Saturday. Then give them an extra 6hrs of sun on Sunday. Then leave them uncovered. They may wilt a little but they will bounce back. They love sun and will reward you for it. The leaves will also dry faster after you water them in the morning.

this is great advice! thank you, i will try it. It's interesting, the leaves that are peaking out from under the cloth are the greenest! i will take the cloth down - or move it to a different section of the garden that will need it...like tomatoes!