Asked August 30, 2019, 1:30 PM EDT
Oakland County Michigan
Most diseases of turf are fungal, so it may be. If you had to pull weeds from the area, that indicates the grass was thinner in that area, allowing weeds to take hold.
Things to check:
Are these low lying areas or slightly raised areas- that is, do they stay wetter or drier than the sections of turf with no problems? Run a sprinkler calibration test -
Is the soil compacted? Clay soils especially become compacted and roots can die off.
What time of day do you water? leaves should be dry by nightfall to minimize disease issues.
Are any tiny moths flying up when you walk across the lawn? This would indicate sod webworm. https://www.canr.msu.edu/resources/sod_webworm_tips_for_your_lawn
Another insect to check is chinch bug, which causes brown areas-
Does a close look at individual leaves show any different colors like black spots, reddish brown spots, etc? These indicate various fungi.
How short is the grass being mowed? Leaving grass 3-4 inches long after mowing develops thicker grass and deeper roots.
How much sun do the problem areas receive? Shaded to densely shaded areas(less than 9 hours sun) will be thinner and will need over-seeding each year with shade tolerant fescues.
For a fee the MSU Plant Diagnostic lab can give you an opinion and recommend a treatment. You submit a fresh cut sod sample and mail it to the lab on a weekday so that it doesn’t sit over a weekend in a post office or the lab mailroom. Here are the instructions:
“Residential Turf: Include a square of turf from the margin of the diseased area so that both healthy and diseased turf is included. Minimally, the turf square should be 6 inches x 6 inches. An intact layer of soil should remain on the root system. Wrap samples in newspaper and pack in a box for shipment. Do not add moisture to the turf prior to shipment. Provide a detailed description of cultural practices (irrigation, fertilization, pesticide application, etc.) and images of the symptoms in the lawn with the sample.” Lab website- https://pestid.msu.edu
I wouldn’t try a general fungicide yet, because certain diseases need a specific fungicide. Here is a reference for you-
I hope some of these ideas are helpful. Thank you for using our service.