Answer: I don't think the heat is the problem. Both melons are grown in areas as hot and hotter than north central Texas.
Watermelons and cataloupes often produce male blooms first and later start setting female blooms (the female blooms have a miniature fruit attached to the base of the blossom). Your cantaloupes may be about to start setting female blooms if they haven't already.
Another cause of failure to set is poor pollination. If you kill the bees by using insecticides around blooming plants, you inherit their job of pollination. Since the watermelons are setting fruit, I suspect you have bees present. Nevertheless if pollination is inadequate, the failure of seeds to develop can cause a fruit to begin to grow and then shrivel and die.
Once blooms are pollinated and fruit are set they can be lost to blossom end rot. Although the condition is caused by a lack of calcium in the fruit, it is brought about by moisture fluctuations in the soil (too wet to too dry). Keep plants well watered and evenly moist. Add organic matter to the soil if it is sandy and mulch well. You also may want to have a soil test done to make sure your calcium levels are adequate. Your County Extension Office (ph# 817/565-5537) can assist you with having your soil tested. Hope this helps!
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