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UC Pest Management Guidelines


Larvae of lucerne moth.

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)

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/1000 sq ft** Ag Use
R.E.I.+
NonAg Use
R.E.I.+
(trade name)   (hours) (hours)

  Calculate impact of pesticide on air quality
The following materials are listed in approximate order of usefulness in an IPM program, taking into account efficacy and impact on natural enemies and the environment. Not all registered materials are listed. Not all registered pesticides are listed. Always read label of product being used.
 
A. SPINOSAD
  (Conserve) SC Label rates 4 until dry
  MODE OF ACTION GROUP NUMBER1: 5  
 
B. 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.
 
C. BACILLUS THURINGIENSIS ssp. KURSTAKI
  (various products) Label rates 4 until dry
  MODE OF ACTION GROUP NUMBER1: 11.B2
  COMMENTS: Breaks down rapidly in sunlight and washes readily off leaves. Do not irrigate for 2 days after treatment.
 
D. CARBARYL*
  (Sevin) 80WSP 3.673 oz 12 until dry
  MODE OF ACTION GROUP NUMBER1: 1A
 
E. AZADIRACHTIN
  (Azatrol, Neemix) Label rates see comments until dry
  MODE OF ACTION GROUP NUMBER1: 18B
  COMMENTS: Most effective on young larvae. Can be used on both warm and cool season grasses. REI for Azatrol is 4 hours and 12 hours for Neemix.
 
F. PERMETHRIN
  (Astro, etc.) 0.4–0.8 fl oz 12 until dry
  MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: Apply using sufficient water to provide adequate coverage. May cause water quality issues.
 
G. DELTAMETHRIN
  (DeltaGard T & O) 5SC 0.2–0.4 fl oz until dry
  MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: Not for use on sod farms or in commercial seed production. Apply as a broadcast spray in a minimum of 2 gal water/1,000 sq ft. Delay irrigation or mowing for 24 hours after application. May cause water quality issues.
 
** 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 are assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their Web site at http://www.irac-online.org/.
+ Restricted entry interval (R.E.I.) 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
M. L. Flint, UC IPM Program, UC Davis
M. A. Harivandi, UC Cooperative Extension, Alameda County
H. K. Kaya, Nematology, UC Davis
Acknowledgment for contributions to Insect and Mites:
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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