Is that brown area in bluegrass turf caused by water stress, or grubs or billbugs? There’s a way to check.
Grubs or water stress? Identifying the cause of brown turf
By Jim Schild and Gary Stone, Extension Educators, Scotts Bluff County
Is the lawn turning brown because of grubs or billbugs, or is it water stress? This is a common question in recent days, since the weather turned hot.
Both types of damage have the same symptoms, because the grubs chew off roots and the bluegrass plant is not able to take in water, giving the appearance of drought.
An easy way to check for grubs is to pull a handful of grass. If the grass pulls up like a piece of carpet, grubs are a likely culprit. If the grass is well rooted, grubs and billbugs can be ruled out.
Another step in identifying the problem is to poke a regular screwdriver into the ground. The screwdriver generally will penetrate as deep as the moisture in the soil, then stop. In a bluegrass lawn, the screwdriver should penetrate to a depth of 6 inches.
Diseases can also start showing up this time of year. Disease symptoms usually are different from water stress, although some diseases that affect roots may look similar in appearance. Another common turf issue is dog urine spots, which with the extreme hot temps are showing unusual browning. These spots are usually somewhat circular in shape and go from brown to green with no transition area.
Drought stress on turf will start showing up as a blue-gray color on Kentucky Bluegrass, and footprints will remain in the grass were you walked. Later stages of water stress show up as the brown patches normally associated with drought stress.
Watering the stressed areas in the early morning will help these areas recover. Some areas that are compacted or have a thatch layer may not absorb water as readily as other areas in the lawn. Make some notes to core aerate these areas this coming fall, after the temperatures have cooled down and the bluegrass has become more active.
If in doubt about what is causing the brown patches in your lawn, contact your local county Extension office for some help in diagnosis of the problems in your lawn.