Answer: Dark brown circles sound more like a fungal or bacterial disease than an insect problem. I'd pick off the affected leaves so the problem doesn't spread. The browning around the margins of the watermelon leaves can indicate over or under watering, or even overfertilizing. Try watering your plants deeply twice a week during the summer months making sure the water percolates down at least 12". This will encourage deep rooting and fewer problems with heat stress. Hope this helps!
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