Answer: Whew! Sounds like you are running yourself ragged trying to keep your lawn green. There are only a few things that will cause death of a lawn; insects, diseases, poor soil, inadequate water and over/under-fertilization. So, let's start with insect problems. Grubs can cause dead patches in lawns, but the population needs to be large and it's unlikely that newly installed sod would have a population large enough to cause dieback. To check for grubs, do this simple test: take a 2-pound coffee can (or something similar in size) and remove both the top and bottom so you have a cylinder. Push the can 2" into the soil, then fill the can with water and a squirt of dish soap. Grubs will float to the surface. If you count more than 12 grubs, it's time to treat the lawn. If you find fewer, don't waste your money on treatments.
Diseases can attack turfgrass in a hurry. The most likely culprit is Summer Patch, caused by the fungus Magnaporthe poae. It is a disease that occurs during the hot portion of the summer. The initial symptoms are yellow patches 6-12 inches in diameter. The turf in these patches thins and the remaining turf turns bronze in color. If warm weather continues, all of the turf in the patch may die. The dead patches may be colonized by weedy grasses. Soil moisture is important in disease development. Excess irrigation or an absence of irrigation during hot weather may make the disease more severe.
Summer patch is a difficult disease to control but several cultural practices will help reduce disease severity. Turfgrass should be maintained in a vigorous, but not overstimulated, growing condition. A balanced fertilization program is important. Avoid excessive nitrogen fertilization during the summer months. Seventy-five percent of the nitrogen fertilizer should be applied in the fall. The use of acidifying nitrogen sources such as ammonium sulfate has been shown to reduce summer patch severity. Slow-release nitrogen fertilizers should be used for spring fertilization. Mowing heights should be maintained above 2 inches on residential lawns. Thatch reduction is important for suppressing disease development, and infested lawns should be dethatched yearly and/or core-aerated.
Summer patch may develop even with optimal turf care, and certain cultural modifications may be necessary to save the turf. Seriously diseased turf should be watered (syringed) daily in the early afternoon to cool the plants and provide some moisture for the diseased roots.
Several fungicides are labeled for the control of summer patch. Chemical control has not been completely effective in eradicating the disease, but it can reduce disease severity if used in conjunction with good turf management. Timing of fungicide applications is critical for effective control . Make the first preventive application in spring when the soil temperature at a depth of 2 inches remains above 65 degrees F. This varies with geographic location, but generally the first fungicide application should be made in early to mid-May, or about 2 to 3 weeks after the crabgrass germinates. A second application should be made one month after the first. The fungicides azoxystrobin (Heritage), propiconazole (Banner and others), triadimefon (Bayleton and others), and myclobutanil (Eagle) are recommended for the early season, preventive applications. Follow label directions concerning irrigation immediately following fungicide application.
At this point I can only recommend that you (or your landscaper) rake out all of the dead spots (roots and all) and reseed the bare areas. Fall rains should help the seeds germinate quickly. Next spring you can apply a fungicide as outlined above to keep Summer patch from ruining your lawn.
Best wishes with your landscape!
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