Answer: Since you've already treated for insects, it could be a disease. You didn't identify the grass type you're growing, so that makes diagnosis a bit more difficult. Grass may be injured by dog urine. The spots resemble Dollar Spot. The difference is that outside the area of dead grass there is often a zone of grass with luxuriant growth. Heavy watering will wash down excess salts and help the grass recover.
Dollar Spot, caused by the fungi Lanzia spp. and Moellerodiscus spp., produces 23 inch circular patches on creeping bentgrass turf and 4-6 inch circular to blotchy areas on bluegrass lawns. These patches are straw colored. Early in the morning, when the grass is covered with dew, a faint cobwebby growth may be seen on the leaves of affected plants. In the early stages of disease, leaves develop distinct tan-colored spots and bands; quite often a reddish-brown border can be seen on the leaf spots.
Dollar Spot develops at temperatures of 60-85 degrees Fahrenheit with high humidity and low soil moisture. The disease usually develops on lawns which are unfertilized but occasionally occurs on high maintenance lawns under stress. It can be controlled by keeping lawns adequately fertilized and watered and by using a fungicide as necessary. Bluegrass varieties differ in Dollar Spot susceptibility with most being moderately susceptible or moderately resistant.
Hope this information is helpful.
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