Answer: It sounds as though you've done everything right as far as feeding your lawn. Yellow areas in your lawn can have many causes. Whatever the reason, they're unsightly at best and could be signs of bigger problems. The good news is that in most cases these ugly spots can be easily remedied or repaired.
Before proceeding with any type of action, make sure the grass is not turning yellow/brown because it's going dormant. Dormancy is a natural reaction in turfgrasses, prompted by seasonal temperature changes. Cool-season grasses go dormant in the heat of summer, warm-season grasses in winter. Dormancy is a resting period, do not fertilize during dormancy.
Yellowing grass is also a symptom of several lawn diseases. Should there be evidence of disease or insect pests, get a positive identification of the problem before trying to treat it. Your local Cooperative Extension Service can help.
Yellow or brown spots may be the result of a simpler problem. Gasoline spills, over-application of pesticides, foot traffic, scalping the lawn when cutting or mowing with a dull blade can all cause discoloration. Affected areas need to be repaired and reseeded.
The high nitrogen content of dog urine can be especially detrimental to lawn grasses. For yellowing turfgrass due to pet urine, the best treatment is to flush the area with water (as soon as possible - within the hour is best). If you think you can train your pet to "go" elsewhere in the lawn, it's worth a try. You may also want to check with your veterinarian about dietary supplements made to reduce the pH and extra nitrogen in dog urine.
There are leaf spot infections that attack warm- and cool-season grasses. Grass begins to appear gray, tan or brown. Upon closer examination, tan, red or purple spots are evident. Can severely thin or kill turfgrass. You can apply a fungicide to your lawn to control fungal diseases. Be sure to apply according to label directions.
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