I am new to vegetable gardening and have a cantelope planted that is trellised. The lower leaves are yellowing (upper leaves are all green) and I wanted to know if this is a problem. If so, is this due to overwatering? They were planted in compost/peat moss about 3-4 weeks ago from starts at home depot and have grown a lot. They get watered for 15 minutes 3 times a week from my automatic irrigation system by drip line. The cucumber you can see next to it are green from top to bottom.

Here is a link that might be useful: cantelope on left - cucumber on right