Pests in Gardens and Landscapes: Quick Tips

Lawn Insects

Published   4/19

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White grub (masked chafer) larvae.

White grub (masked chafer) larvae.

Cutworm larva.

Cutworm larva.

Dig around roots to look for grubs.

Soil drench test.

Contrary to popular belief, insects are not a common cause of lawn damage in California. Poor lawn care, especially incorrect watering or planting grass varieties not suited to your area, is the most likely cause of unhealthy or dying lawns. Turfgrass diseases and dog urine also produce similar damage. Never apply an insecticide unless a damaging level of a known insect is confirmed. Insecticides are only effective if applied at the right time and in the right manner. Many insecticides also kill good bugs—use them only as a last resort.

Keep your lawn healthy.

  • Plant grass species best suited for your area.
  • Over-seed thin areas in the spring and fall.
  • Water deeply and infrequently.
  • Perform routine maintenance on sprinkler heads.
  • Apply fertilizer appropriately.
  • Aerate your lawn annually; remove thatch if it exceeds 1/2 inch.
  • Cut only 1/3 of grass height at each mowing and keep lawnmower blades sharp.

How do you know if insects are causing damage?

  • Brown spots in lawns can have different causes. Over- or under-watering, plant disease, over-application of fertilizer/herbicide or chemical spill, and dog urine all cause similar looking damage.
  • Before applying an insecticide, confirm that insects are present at high enough numbers to cause damage .
    • For grubs, dig around roots. You do not need to treat if there are 5 or fewer grubs per square foot.
    • For other insects, perform a drench test (described on reverse).
  • If you do not find live pest insects at high levels, do not treat with pesticides.

What about pesticides?

  • Before applying insecticide, try to alter your lawn environment to discourage the pest.
  • If an insecticide is required, select the least toxic product available for the pest you are targeting. Time treatments appropriately to be effective.
  • Insect-attacking nematodes control caterpillars or grubs.
  • Find out which insecticide targets your pest:
    • Bacillus thuringiensis (Bt) and spinosad are least toxic pesticides that kill caterpillars.
    • Azadirachtin controls cutworms, armyworms, and larvae of lawn moths.
    • Imidacloprid controls young lawn grubs but can injure bees on flowering weeds and earthworms.
    • Avoid products containing carbaryl and pyrethroids (e.g., bifenthrin). These are broadly toxic insecticides that kill chinch bugs, grubs, lawn moths, and cutworms, but also kill beneficial insects and pollute waterways.

How to perform a drench test:

  • Measure out an area of lawn that equals 1 square yard.
  • Mix 3–4 tablespoons of dishwashing liquid to 2 gallons of water.
  • Evenly apply the 2 gallons to 1 square yard of your lawn.
  • Watch the area for 10 minutes and count the number of caterpillars that rise to the surface.
  • Treat the area only if insect numbers exceed 5 armyworms or cutworms or 15 lawn moth larvae per square yard.

Read more about Lawn Insects. See also UC Guide to Healthy Lawns.

Minimize the use of pesticides that pollute our waterways. Use nonchemical alternatives or less toxic pesticide products whenever possible. Read product labels carefully and follow instructions on proper use, storage, and disposal.

Statewide IPM Program, Agriculture and Natural Resources, University of California
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Agriculture and Natural Resources, University of California

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