Build Up the Low Yellow Spots
The makers and sellers of pest and fungus treatments would love you to believe that every yellow or dead spot is the result of a sinister invader that can be eliminated with frequent use of their expensive products. But some yellow spots are simply the result of low spots in your lawn, especially if they appear after heavy rain. Grass can suffocate or rot in standing water. Try spreading a layer of compost over the yellow spot to raise it up to the level of the surrounding ground. Within a week or two, new grass will likely sprout to fill the patch.