Soory for the slow reply. I see symptoms of possible disease, nutrient deficiency, and or possibly overwatering. Here is a fact sheet that covers many of the common diseases of watermelon - https://extension.okstate.edu/fact-sheets/watermelon-diseases.html. Samples may be needed to determine the actual problem. For additional assistance and to submit samples for diagnosis please contact your local Oklahoma County OSU Extension Center - https://extension.okstate.edu/county/oklahoma/.