Is It Heat Damage or Lawn Insects?

Brown lawn damage can be caused by heat stress, uneven sprinkler coverage or lawn insects. Photo by Salvador.

August can be a difficult month for lawns in Southern Idaho. Hot afternoons, dry wind, reflected heat from concrete and uneven sprinkler coverage can quickly cause yellow or brown patches. Unfortunately, lawn insects can create many of the same symptoms.

From a distance, heat-stressed grass and insect-damaged grass may look almost identical. Identifying the cause before making changes is important. Otherwise, you may waste water trying to fix an insect problem or apply an insect treatment when the lawn simply is not receiving even coverage.

Here are a few ways to tell what may be happening in your lawn.

Signs Your Lawn May Be Suffering From Heat or Drought Stress

Heat stress usually begins in the hottest and driest parts of a property. Common trouble spots include:

• Lawn edges next to sidewalks, driveways and curbing

• Narrow park strips surrounded by concrete

• Slopes or areas exposed to afternoon sun

• Corners and sections between sprinkler patterns

• Areas blocked by shrubs, vehicles or other obstacles

  
  

Before grass turns completely brown, it may develop a dull gray or bluish-green color. The blades may begin to fold or curl, and footprints can remain visible because the grass does not spring back quickly.

Dry soil is another important clue. A few hours after the sprinklers have finished, push a long screwdriver or soil probe into both a healthy section and the damaged section. If it is much harder to push into the brown area, that part of the lawn may not be receiving enough water.

Do not assume the entire lawn needs a longer watering cycle. Run each sprinkler zone during the day so you can watch it operate. Look for:

• Clogged filters or nozzles

• Broken, tilted or sunken sprinkler heads

• Heads that are not rotating correctly

• Spray blocked by overgrown grass or plants

• Low pressure or shortened spray patterns

• Water landing on pavement instead of the lawn

• Areas where neighboring sprinkler patterns do not overlap

Correcting one coverage problem is often more effective than increasing the watering time for every zone. The University of Idaho recommends checking sprinkler spray patterns, soil moisture and possible soil compaction when isolated dry spots develop.

Signs Lawn Insects May Be Responsible

The University of Idaho identifies sod webworms, white grubs and billbugs as three common turf insects in the state. Their damage can become more noticeable during hot weather because damaged grass cannot take up water normally.

Billbugs

Billbug damage is especially easy to mistake for drought stress. These insects are a known turf problem in the Boise–Twin Falls region. Their larvae feed in grass stems, crowns and roots, causing irregular yellow or brown patches during the summer.

Gently pull on the damaged grass. Billbug-damaged blades may break away easily at the crown. You may also find a sawdust-like material near the base of the grass. The larvae are small, creamy white with brown heads and do not have visible legs.

Sod Webworms

Sod webworm larvae feed on grass leaves and stems near the surface. Early damage may appear as small brown areas that look closely clipped or scalped. As feeding continues, the patches can join together and form larger irregular areas. Grass blades may also look chewed or shredded.

Small tan or whitish moths sometimes fly up while mowing or walking across the lawn. That can be a clue, although seeing moths alone does not confirm damaging numbers of webworms. The larvae usually hide in silk-lined tunnels in the thatch during the day.

White Grubs

White grubs feed below the surface and damage the lawn's roots. When root loss becomes severe, the turf may feel loose or spongy and can sometimes be rolled back like a piece of carpet. You may find creamy white, C-shaped grubs with brown heads and six legs in the upper few inches of soil.

Birds or animals digging repeatedly in the same area can also indicate insects below the surface, but digging alone is not enough to identify the specific pest.

Three Simple Checks You Can Do

1. Check the moisture

Probe the soil after watering and compare damaged areas with healthy turf. Dry soil points toward a watering, coverage or soil-compaction problem. Moist soil does not automatically rule out heat stress, but it is a reason to investigate further.

2. Try the tug test

Gently pull on the grass at the edge of the damaged patch. Heat-stressed grass usually remains firmly rooted. Grass affected by billbugs or grubs may pull loose because the crown or roots have been damaged.

3. Inspect the edge of the patch

The transition between healthy and damaged turf is usually the best place to look. Check the thatch and top few inches of soil for larvae, chewed blades, loose roots or sawdust-like material. The completely dead center of a patch may no longer contain the insects that caused the original damage.

Heat Stress and Insect Damage Can Happen Together

Sometimes the answer is not one or the other. A lawn with poor sprinkler coverage is already under stress and may show insect damage sooner. Likewise, insects that damage the roots make it harder for grass to survive hot weather, even when the sprinklers are running regularly.

That is why simply adding more water or applying a general insecticide may not solve the problem. The pest should be identified before treatment because the correct product and timing depend on the insect and its life stage. Not every insect found in a lawn is harmful.

If the soil is moist and the grass is still firmly rooted, other possibilities may need to be considered, including disease, compacted soil, thick thatch or a recent chemical injury.

What Should You Do Next?

Start by checking sprinkler operation and moisture levels. If coverage is uneven, repair or adjust the system before deciding the lawn needs additional water. If the grass pulls up easily or you find larvae, feeding damage or other insect evidence, have the lawn properly evaluated before applying a treatment.

Once the cause has been corrected, some heat-stressed grass may recover with improved watering. Areas with severe crown or root damage may need to be reseeded or replaced. Late summer into early fall is generally the best period for establishing cool-season turf in Idaho, but the underlying sprinkler, soil or insect problem should be corrected first.

Need Help Diagnosing Brown Spots?

One Call Property Solutions provides sprinkler inspections and repairs, lawn fertilization, weed control and lawn insect treatments throughout Twin Falls and the surrounding Magic Valley. We can check sprinkler coverage, look for signs of insect activity and recommend the appropriate next step for your lawn.

Call 208-490-6713 or submit a work request at onecallps.com to schedule service.