bad grass spot in lawn
Front lawn has had new sod installed twice in the last eight years. There has always been a brown spot in that part of lawn. First time, after removal of old sod we asked to have an insecticide applied before sod. Was told it was not necessary. Also asked for dirt base to be raked and rolled. Was told that 'we don't do that anymore'. The whole experience was unpleasant. And in a year the brown spot was back. A few years later we had another lawn service come in and remove old sod. They did rake, level and roll it and installed new sod. (I don't think they applied insecticide). Job was done well. Still a couple of years later, spot is back. There are a couple of smaller brownish spots distant from large spot. I had some Dursban from a few years back and applied that to lawn a couple of years ago. Didn't do any good. Can you tell what is causing it and a remedy? Lawn gets regular fertilizer and mowing/edging.
Multnomah County Oregon
Thank you for choosing Ask an Expert for help with your lawn. Your observation that the damage appears in the same spot each year leads me to believe that there is something amiss in the soil.
If this was at the top of a slope, I might think that irrigation water is running over the soil and not sinking in, to wet the grass roots. If it was at the bottom of a slope or in a low spot, I might think that irrigation water was pooling there and rotting the roots. However, from the photos, neither one seems to be the case.
Occasionally, builders bury chunks of construction debris (wood, concrete, sheet rock) in a yard, and grade the soil over everything. This certainly could affect the root zone of anything trying to grow in the area.
Alternatively, there are many underground springs and waterways in the Portland area flowing below homes, backyards, and parks that could make one section of a property just a bit wetter than the rest. In addition, some fungus diseases attack in places where the soil is overly wet. I cannot see individual blades to determine whether there are fungus spots or other signs of disease, but I do note some yellowing in the upper part of photo three, which may be a disease.
The pattern of damage does not rule out insect attack, but your use of the insecticide should have taken care of most of the usual culprits.
I’m sorry that I cannot supply a definitive answer. For now, I would rake out the dead grass, check the moisture in the soil that area compared to nearby vigorous areas. If it seems comparable, over-seed with a sun/shade blend, and continue with standard maintenance.
For a look at best practices for lawn care in our area, I recommend the Oregon State University publication, “Practical Lawn Care for Western Oregon”, see here: https://catalog.extension.oregonstate.edu/ec1521