Lawn Disease not Grubs Causing Brown Spots

Lawn disease, not grubs may be the cause of brown spots on your lawn.
By Richard C. Fry
May/June 1987
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I suspect that the previous owners used lots of chemicals, and when you cut back, your lawn went through a withdrawal stage, during which it was weakened and susceptible to diseases.

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My problem is grubs. 

When I bought my home four years ago, I also bought the best-looking lawn on the block. The previous owners, a retired couple, had worked that yard all day every day. I decided to make it even better, so I sprinkled some compost from my back yard pile (one cubic foot of leaves and table scraps) on the less luxuriant places. 

The next year, brown spots appeared where I had applied the compost. Although I saw no grubs, I figured that's what it had to be, so I sprayed the areas with nicotine. To no avail: The compost-treated grass finally died completely. 

The next year, the brown spots appeared again. Again, nicotine didn't faze the grubs. 

Last year I reseeded my lawn. It was beautiful—until July, when (you guessed it) the same brown spots showed up. 

This year I'm considering cementing in the entire yard and having the best-looking patio on the block. Before I do, any ideas? I can't see it being lack of water; I water almost every day.  

Lawn Disease not Grubs Causing Brown Spots

It sounds to me as if your problem is not grubs but lawn disease. Here's how you can tell: Grubs chew off the grass roots, so if the pests have been at your lawn, you should easily be able to lift patches of dead grass off the soil. If the dead grass is still tightly rooted, chances are you've got one or more of the warm-season lawn diseases. These are in the soil year-round, but they're most obvious during hot, humid periods.

It's interesting to speculate why the problem occurred when and where it did. I suspect that the previous owners used lots of chemicals, and when you cut back, your lawn went through a withdrawal stage, during which it was weakened and susceptible to diseases. It's also possible that your compost pile—which is extremely small—didn't “cook” hot enough, so that diseases in incompletely composted matter transferred themselves to your lawn.

I'd recommend several things. First, get a sample of your dead turf—preferably near the outer edge where you can also get some healthy grass and take it to your county agricultural extension agent. Second, reseed the damaged areas with a disease-tolerant turf grass variety appropriate for your area, and apply a low-nitrogen organic fertilizer in June. Finally, I'd suggest you replace the daily sprinklings with deep, weekly watering.

— Richard C. Fry, horticulturist 

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