How to Manage Pests

UC Pest Management Guidelines

Turfgrass

Sod Webworms

Scientific Names:
Lucerne moth: Nomophila noctuella
Western lawn moth: Tehama bonifatella
Sperry's lawn moth:Crambus sperryellus

(Reviewed 9/09, updated 9/09, pesticides updated 12/16)

In this Guideline:


DESCRIPTION OF THE PESTS

Adult sod webworms, called lawn moths, are typical snout moths: they have sensory appendages called labial palps that extend in front of the head. The moth holds its wings close to and over its body at rest, giving it a slender appearance. When disturbed, the moth makes a short flight close to the grass. At night, these moths drop their eggs indiscriminately on to turf. The creamy larvae have a distinctive double row of brown or black spots down their backs, located at the base of long bristles. The Lucerne moth larva is somewhat larger than the other sod webworm larvae. During the day larvae reside in silk-lined burrows, writhing when disturbed. At night they emerge to feed.

SUSCEPTIBLE SPECIES

Bluegrasses and bentgrasses often suffer the most damage, while perennial ryegrasses and turf-type tall fescues infected with endophytes (symbiotic fungi) and warm-season turfgrasses are more resistant.

DAMAGE

First instar sod webworm larvae are leaf skeletonizers. Later instars notch or cut off leaf blades and pull them into the burrow. Heavily infested turf (more than 100/sq. yd.) quickly appears moth eaten, with irregular patches of brown grass or bare areas. Significant damage can occur on drought-affected bluegrass and on bentgrass green and tee areas. Lucerne moths are primarily a problem where clover and dichondra are mixed with turfgrass.

MANAGEMENT

When sod webworms are present, dethatching the turfgrass may help. Monitor to determine if treatment is needed. Treatment choices include parasitic nematodes and Bacillus thuringiensis (Bt).

Biological Control

Natural enemies in California include a parasitic tachinid fly and two parasitic braconid wasps, along with earwig, rove beetle, robber fly, paper wasp, ant, and vertebrate predators. The extensive soil or thatch contact of sod webworms makes Steinernema carpocapsae nematodes a valuable control measure. Bacillus thuringiensis ssp. kurstaki (Bt), a microbial insecticide, can be used but it breaks down rapidly in sunlight, washes readily off leaves, and is ineffective against late instar larvae.

Cultural Control

Thatch removal can assist in removing sod webworm habitat, although larvae do not require a thatch layer to be present in very high numbers. Control of clover and dichondra may help minimize damage. Damage is usually not noticeable in turf mowed at heights above 2.5 inches.

Monitoring and Treatment Decisions

Monitor for these pests from June to early October. Consider treating only when a drench test (see section on MONITORING AND TREATING INSECTS AND MITES) indicates there are more than 5 larvae per square yard on stressed greens or 15 larvae per square yard in other situations. If Bt is used, apply it when there are predominantly early instar larvae. Other materials are also most effective on small larvae but will kill larger ones more effectively.

Mow and irrigate the site before applying insecticide and do not mow or irrigate the turfgrass for at least 24 hours after treatment unless nematodes were applied, in which case apply a post-treatment irrigation. When Bt is applied, do not irrigate for 2 days after treatment.

Common name Amount per 1000 sq ft** Ag Use
REI‡
NonAg Use
PHI‡
(Example trade name)   (hours) (days)

UPDATED: 12/16
Calculate impact of pesticide on air quality
Bee precaution pesticide ratings
The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Not all registered pesticides are listed. Always read the label of the product being used.
 
A. SPINOSAD
  (Conserve) SC Label rates 4 Until dry
  MODE-OF-ACTION GROUP NUMBER1: 5
  COMMENTS: Toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.
 
B. BACILLUS THURINGIENSIS ssp. KURSTAKI
  (various products) Label rates 4 Until dry
  MODE-OF-ACTION GROUP NUMBER1: 11A
  COMMENTS: For young cutworm larvae. Apply to early instar larvae. Repeat application may be necessary. Breaks down rapidly in sunlight and washes readily off leaves. Do not irrigate for 2 days after treatment.
 
C. BACILLUS THURINGIENSIS ssp. AIZAWAI
  (various products) Label rates 4 Until dry
  MODE-OF-ACTION GROUP NUMBER1: 11A
  COMMENTS: For young armyworm larvae. Apply to early instar larvae. Repeat application may be necessary. Breaks down rapidly in sunlight and washes readily off leaves. Do not irrigate for 2 days after treatment.
 
D. STEINERNEMA CARPOCAPSAE 25 million NA NA
  COMMENTS: Store nematodes properly before use as directed. Apply to warm, moist, but not soggy soil. Several irrigations may be needed during 2 weeks after application to keep soil moist. Apply during the coolest time of day in hot areas.
 
E. AZADIRACHTIN
  (Azatrol, Neemix) Label rates 4 Until dry
  MODE-OF-ACTION GROUP NUMBER1: un
  COMMENTS: Most effective on young larvae. Can be used on both warm- and cool-season grasses.
 
F PYRETHRINS
  (various products) Label rates See label See label
  MODE-OF-ACTION: 3A
 
G. CHLORANTRANILIPROLE
  (Acelepryn) Label Rates 4 Until dry
  (Acelepryn G) Label Rates 4 After application complete
  MODE-OF-ACTION GROUP NUMBER: 28
 
H. CLOTHIANIDIN
  (Arena 50 WDG) Label rates 12 Until dry
  (Arena 0.25 G) Label rates 12 When dust has settled.
  MODE-OF-ACTION GROUP NUMBER1: 4A
  COMMENTS: Toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.
 
I. CARBARYL*
  (Sevin SL) Label rates 12 Until dry
  MODE-OF-ACTION GROUP NUMBER1: 1A
  COMMENTS: Nontarget effects likely on other soil-dwelling organisms. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.
 
J. BIFENTHRIN
  (Talstar) Label rates Until dry
  MODE-OF-ACTION GROUP NUMBER1: 3A
  COMMENTS: Not for use on sod farms or in commercial seed production. May cause water quality issues. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.
 
** Apply in 25 gal water/1000sq ft.
* Permit required from county agricultural commissioner for purchase or use.
1 Rotate chemicals with a different mode-of-action group number, and do not use products with the same mode-of-action group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a group number of 1B; chemicals with a 1B group number should be alternated with chemicals that have a group number other than 1B. Mode-of-action group numbers ("un"=unknown or uncertain mode of action) are assigned by IRAC (Insecticide Resistance Action Committee).
Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Agricultural use applies to sod farms and commercial seed production.
NA Not applicable.
Indicates use is not listed on label.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Turfgrass
UC ANR Publication 3365-T

Insects and Mites

A. M. Sutherland, UC Statewide IPM Program, Alameda County
M. L. Flint, UC IPM Program, UC Davis
M. A. Harivandi, UC Cooperative Extension, Alameda County

Acknowledgment for contributions to Insect and Mites:
H. K. Kaya, Nematology, UC Davis
J. Hartin, UC Cooperative Extension, San Bernardino County
R. S. Cowles, Connecticut Agricultural Experiment Station, Windsor, CT
K. Kido, Entomology, UC Riverside
H. S. Costa, Entomology, UC Riverside
D. D. Giraud, UC Cooperative Extension, Humboldt/Del Norte counties

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