Answer: Cucumbers and melons are potentially subject to a variety of diseases that can cause wilting and death. Sometimes this is related to which specific varieties you are growing, since some are more disease resistant than others. The diseases can be carried by insects or in the soil or by spores in the air (such as mildew). Too, there are insects that can cause a plant to wilt by boring into the stem. Physical damage to the stem such as breakage can also cause severe wilting and dieback. Based on your description I am not able to diagnose the problem(s) with your plants. You might want to consult with your local county extension to try to obtain a more specific diagnosis and based on knowing that, see if there is anything you can do to protect the rest of your plants. I'm sorry I can't be more specific long distance.
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