COLUMN: Grubs not always the culprit for brown patches in the lawn

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By Jeneen Wiche

Whenever brown patches or dead spots appear in the lawn, we are quick to suspect a grub infestation. This is not always the case, though. In fact, contemporary lawn care routines may be more to blame than you realize. Some lawn care habits encourage disease and/or make your lawn more desirable to Japanese beetles and masked chafer beetles, both of which deposit the eggs that grow into grubs.
The most common disease for lawns around here is brown patch (which is sometimes blamed on grubs). Circular brown patches will begin to show in tall fescue after hot summer weather. Throw in a couple of rainy days and you see the patches begin to develop. Patches range in size from a couple of inches to three feet.
One of the reasons we see more brown patch in Kentuckiana lawns is, indeed, bad habits. Lawns that receive too much nitrogen in the spring and summer are susceptible; lawns that are mowed too short and mowed when wet are more susceptible; and lawns that are irrigated on a regular basis are more susceptible. This seems to be the care profile for those who stress about a perfect lawn. Ease up a bit.
If grubs cause brown patches, it is basically too late to treat once you notice the dead spots. If the problem is actually grubs, you will be able to lift the dead sod away because the grubs feed on the roots, effectively severing them at the soil surface.
When we have dry conditions during egg laying, we typically see larger infestations in irrigated turf. A green, lush lawn in a drought cycle will be like a beacon in the night for beetles looking for a place to lay eggs. A higher rate of egg-hatch occurs in warm, moist soil, too.
Grub control takes place June through mid-August. Egg-hatch for most lawn grubs is in mid-July. Use Milky Spore instead of chemical insecticides if you can confirm a grub problem. The excessive use of lawn chemicals and fertilizers ends up polluting our waterways more than controlling a pest problem.
Other potential causes for brown colored patches in the lawn include debris just beneath the surface, which impedes good root development making that area more susceptible to heat and drought stress. We have quite a bit of limestone in western Shelby County, so when we experience drought, there are certain areas that brown out first due to rock just beneath the surface. We have been in a cycle of drought after all.
Animal urine certainly can kill the grass, too. Often you will see a brighter green ring around the dead patch because of the extra nitrogen the urine leaves behind. Oddly enough, it both kills and feeds the grass.
I have essentially quit fertilizing the lawn. There is simply too much of it at the farm, and I have come to love my toads more than a fast grass green-up in the spring.
If you must fertilize, however, do so in the fall so that the extra nitrogen helps to establish a healthier root system.
Do not fertilize in the spring – fertilizer is used up by the grass in rapid spring growth (and it contributes to summer fungal diseases like brown patch), or it runs off into the storm drain during frequent spring rains.