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Lawn & turf

Before blaming bugs, check the watering. UC IPM says insects are not a common cause of damage to home lawns in California, and that poor irrigation is the most common cause. Purdue calls billbugs the most commonly misdiagnosed insect problem in North American turf, usually taken for drought, disease or grubs. A patch of chinch bug damage looks like drought until you do a float test. So find the insect and count it first.

The count tells you what to do. Grubs are counted by cutting back a square foot of turf and looking through the turf and the top 2–4 inches of soil. Caterpillars are brought up with a soap flush: UC IPM uses 3–4 tablespoons of dishwashing liquid in 2 gallons of water over 1 square yard, and counts what surfaces in 10 minutes. White grubs are the larvae of Japanese beetles, June bugs and other scarabs, and most extension services treat only above about five to ten per square foot. May/June beetle grubs are the exception: UMass sets 2–4 and the Northeastern IPM Center 3–5 per square foot. Below the threshold, water and mow well and leave them.

Beneficial nematodes are the biological control that covers the most lawn insects. They go on in the evening onto moist soil, are watered in straight away, and need the soil kept moist afterwards, and results vary. In the South, mole crickets and fire ants add their own problems. For fire ants, Texas A&M recommends its Two-Step bait method and says grits, club soda and the other home remedies do not work.

crop context · lawn with a brown patch, late summer

The lawn insects worth counting

APRIL–JUNE

Cutworms

Small dead or sunken spots, with grass often clipped close around aeration holes where the larvae hide. UC IPM treats at 5 per yd² in a soap flush.

ReleaseSteinernema carpocapsae25 million per 1,000 ft² (about 270,000 /m²)
JUNE–AUGUST

Billbugs

Stems snap off at the soil, packed with sawdust-like frass. Act at 1 or more larvae per cup-cutter core.

ReleaseHeterorhabditis bacteriophoraAbout 1 billion per acre (≈250k /m²)
JUNE–SEPTEMBER

Chinch bugs

Yellow, then brown patches in the sunniest, driest turf. Float-test first. Thresholds vary: 15–30 per ft² (Penn State, Clemson) up to 30–50 nymphs (UMass).

ReleaseBig-eyed bugsWild — not sold; conserve the ones already in the lawn
JULY–SEPTEMBER

Sod webworms

Small ragged brown patches in sunny lawns, with larvae in tunnels in the thatch. UC IPM treats at 15 per yd²; UMass says damage often does not warrant treatment.

ReleaseSteinernema carpocapsae25 million per 1,000 ft² (about 270,000 /m²)
AUGUST–OCTOBER

White grubs

Turf browns and rolls back like a loose carpet, and skunks and birds dig for them. Treat above about 5–10 per ft² (UMass: from 2–4 for May beetle grubs to 12–20 for Asiatic garden beetle).

ReleaseHeterorhabditis bacteriophoraAbout 25–50 million per 1,000 ft² (250k–500k /m²)
AUGUST–OCTOBER

Fall armyworm

Larvae move across the lawn as a group, leaving a sharp line between eaten and green grass. UC IPM treats armyworms at 5 per yd².

ReleaseSteinernema carpocapsae25 million per 1,000 ft² (about 270,000 /m²)
MARCH–JUNE & LATE AUG–OCT · SOUTHEAST

Mole crickets

Tunnels loosen the soil and roots are eaten, so grass looks drought-struck even when watered. Act at 2–4 per 4 ft² surfacing within 3 minutes of a soap flush.

ReleaseSteinernema scapterisciNot on sale — no current product
BAIT LATE AUG–MID OCT · SOUTH

Red imported fire ant

Loose soil mounds in sunny lawns and painful stings. Texas A&M says the Two-Step method suits yards with five or more mounds per quarter-acre.

ReleaseNothing to releaseTwo-Step: bait the yard, then treat problem mounds

Season calendar

US LAWNS · QUALITATIVE READING OF EXTENSION SOURCES
JFMAMJJASOND
CutwormsJan: QuietFeb: QuietMar: QuietApr: BuildingMay: Pest pressure highJun: Pest pressure highJul: BuildingAug: BuildingSep: BuildingOct: QuietNov: QuietDec: Quiet
BillbugsJan: QuietFeb: QuietMar: QuietApr: BuildingMay: BuildingJun: Pest pressure highJul: Pest pressure highAug: Pest pressure highSep: BuildingOct: BuildingNov: QuietDec: Quiet
Chinch bugsJan: QuietFeb: QuietMar: QuietApr: BuildingMay: BuildingJun: Pest pressure highJul: Pest pressure highAug: Pest pressure highSep: Pest pressure highOct: BuildingNov: QuietDec: Quiet
Sod webwormsJan: QuietFeb: QuietMar: QuietApr: BuildingMay: BuildingJun: BuildingJul: Pest pressure highAug: Pest pressure highSep: Pest pressure highOct: BuildingNov: QuietDec: Quiet
White grubsJan: QuietFeb: QuietMar: QuietApr: BuildingMay: BuildingJun: QuietJul: BuildingAug: Pest pressure highSep: Pest pressure highOct: BuildingNov: QuietDec: Quiet
Fall armywormJan: QuietFeb: QuietMar: QuietApr: QuietMay: QuietJun: QuietJul: BuildingAug: Pest pressure highSep: Pest pressure highOct: Pest pressure highNov: QuietDec: Quiet
Mole crickets (Southeast)Jan: QuietFeb: QuietMar: BuildingApr: Pest pressure highMay: Pest pressure highJun: BuildingJul: BuildingAug: Pest pressure highSep: Pest pressure highOct: Pest pressure highNov: BuildingDec: Quiet
Grub nematode windowJan: QuietFeb: QuietMar: QuietApr: QuietMay: QuietJun: QuietJul: QuietAug: Release windowSep: Release windowOct: QuietNov: QuietDec: Quiet

Starter program

Not a calendar of releases: a lawn gets nematodes only when a count passes the threshold. This is the order of checks through a season.

  1. APRIL–JUNESoap-flush for cutworms3–4 tbsp dishwashing liquid in 2 gal of water over 1 yd²; count what surfaces in 10 minutes
  2. JUNE–JULYTug-test for billbugsStems that snap at the soil and hold frass; confirm the larvae before treating
  3. SUMMER, SUNNY PATCHESFloat-test for chinch bugsAt the edge between brown and green grass; drought alone looks the same
  4. AUGUSTHeterorhabditis bacteriophoraOnly if grubs pass 5–10 per ft²: 25–50 million per 1,000 ft², watered in
  5. ON FINDING CATERPILLARSSteinernema carpocapsae25 million per 1,000 ft² in the evening, onto moist soil, for sod webworms, cutworms and armyworms

Setting up the garden

Nematodes are living animals, and most failures in lawns come from letting them dry out.

Keep the soil moist for two weeks

Water before and straight after application. BASF says grub nematodes need moist soil at 12–30 °C (54–86 °F) for at least two weeks, and UMass warns S. carpocapsae is very vulnerable to drying out.

Apply at dusk or early morning

Put them on in the evening or early morning and water them in at once, so they are carried into the root zone.

Expect variable results

Nematodes are the main biological option for grubs, but Kentucky finds them less consistent than conventional insecticides. Milky spore affects only Japanese beetle grubs.

Sort the float-test catch

Big-eyed bugs float up with chinch bugs. A broad head and bulging eyes means a predator, so leave it out of the count.