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How to Manage Pests
UC Pest Management Guidelines
Turfgrass
Cutworms and Armyworms
(Reviewed 9/09,
updated 9/09)
In this Guideline:
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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.
All turfgrass species.
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.
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) |
|
| 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. |
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| A. |
SPINOSAD |
| |
(Conserve SC) |
Armyworms: 0.25–1.2 fl oz |
4 |
until dry |
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Cutworms: 0.8–1.2 fl oz |
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MODE OF ACTION GROUP NUMBER1: 5 |
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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. |
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| B. |
STEINERNEMA CARPOCAPSAE |
25 million |
NA |
NA |
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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. |
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| C. |
BACILLUS THURINGIENSIS ssp. KURSTAKI |
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(various products) |
Label rates |
4 |
until dry |
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MODE OF ACTION GROUP NUMBER1: 11.B2 |
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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. |
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| D. |
BACILLUS THURINGIENSIS ssp. AIZAWAI |
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(various products) |
Label rates |
4 |
until dry |
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MODE OF ACTION GROUP NUMBER1: 11.B1 |
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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. |
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| E. |
AZADIRACHTIN |
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(Azatrol, Neemix) |
Label rates |
see comments |
until dry |
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MODE OF ACTION GROUP NUMBER1: 18B |
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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. |
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| F. |
CARBARYL* |
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(Sevin) |
3 oz |
12 |
until dry |
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MODE OF ACTION GROUP NUMBER1: 1A |
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| G. |
BIFENTHRIN |
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(Talstar) |
Label rates |
— |
until dry |
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MODE OF ACTION GROUP NUMBER1: 3 |
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COMMENTS: Not for use on sod farms or in commercial seed production. May cause water quality issues. |
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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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