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How to Manage Pests

UC Pest Management Guidelines


Variegated cutworm larva.

Turfgrass

Cutworms and Armyworms

Scientific Names:
Black cutworm: Agrotis ipsilon
Variegated cutworm: Peridroma saucia
Granulate cutworm: Agrotis subterranea
Armyworm: Mythimna (= Pseudaletia) unipuncta

(Reviewed 9/09, updated 9/09)

In this Guideline:


DESCRIPTION OF THE PESTS

Cutworms and armyworms are larvae of heavy-bodied, night-flying moths in the family Noctuidae. The white or greenish eggs of these noctuids are laid in masses, darkening as they approach hatching. Larvae can grow up to 2 inches (5 cm) long and typically curl up and lie still when disturbed.

Although damage is similar, armyworms are distinct from cutworms in their behavior. While cutworms are usually solitary feeders, armyworm eggs are laid in masses and larvae will feed as a group. When populations are high and food is scarce, armyworms will move as a group, feeding indiscriminately on plants in their path. Variegated cutworms are also known to march like armyworms when populations are high.

SUSCEPTIBLE SPECIES

All turfgrass species.

DAMAGE

Cutworms and armyworms are active from mid-March to October. They feed on leaves and crowns and may cut off plants near the soil surface. Larvae feed at night and hide in the thatch layer or in a burrow in the soil during the day. Turfgrass may be closely clipped around aeration holes, which larvae commonly occupy. Damage appears as circular spots of dead grass or depressed spots. Armyworms, especially, prefer damp areas.

MANAGEMENT

Manage armyworms or cutworms by dethatching the turfgrass and ensuring that irrigation does not cause wet areas in the turf. When monitoring indicates a need to treat, treatment choices include parasitic nematodes and Bacillus thuringiensis (Bt).

Biological Control
Larvae are parasitized by braconid wasps (Apanteles spp.) and by tachinid flies. Birds also commonly feed on armyworms and cutworms. The extensive contact noctuid larvae have with soil or thatch makes Steinernema carpocapsae nematodes a valuable control measure.

Cultural Control
Remove thatch to eliminate much of the daytime resting habitat for larvae. Avoid wet areas by irrigating according to evapotranspiration needs of turfgrass, because armyworms prefer laying eggs in damp areas containing stressed plants.

Monitoring and Treatment Decisions
Threshold levels are five larvae per square yard. Conduct a drench test (see MONITORING AND TREATING INSECTS AND MITES) to determine the infestation level. Consider treatment when there are more than five larvae per square yard. 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. Bacillus thuringiensis subsp. kurstaki (Bt) is not as effective against cutworms and armyworms as for sod webworms and should only be used on younger larval stages (first and second instars). 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.
 
A. SPINOSAD
  (Conserve SC) Armyworms: 0.25–1.2 fl oz 4 until dry
    Cutworms: 0.8–1.2 fl oz    
  MODE OF ACTION GROUP NUMBER1: 5
  COMMENTS: Use lower rate for control of light infestations of small larvae; the higher rate should be used for control of heavy infestations and large larvae. Delay watering or mowing of treated area for 12–48 hrs after treatment. Do not reapply within less than 7 days.
     
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: 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.
 
D. BACILLUS THURINGIENSIS ssp. AIZAWAI
  (various products) Label rates 4 until dry
  MODE OF ACTION GROUP NUMBER1: 11.B1
  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.
 
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. The REI for Azatrol is 4 hours; for Neemix it is 12 hours.
 
F. CARBARYL*
  (Sevin) 3 oz 12 until dry
  MODE OF ACTION GROUP NUMBER1: 1A
 
G. BIFENTHRIN
  (Talstar) Label rates until dry
  MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: Not for use on sod farms or in commercial seed production. May cause water quality issues.
 
** Apply spray in 25 gal water/1000 sq 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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