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UC Pest Management Guidelines


Variegated cutworm larva.

Bermudagrass Seed Production

Cutworms and Armyworm

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

(Reviewed 1/07, updated 4/10)

In this Guideline:


DESCRIPTION OF THE PESTS

Cutworm larvae can have various colors and patterns, but the heavy-bodied larvae always appear as smooth-skinned caterpillars to the naked eye. They may measure up to 2 inches (5 cm) long. They feed at night and frequently roll into a C-shape when disturbed. Cutworm adults are night-flying moths in the family Noctuidae. The white or greenish eggs of these noctuids are laid in masses, darkening as they approach hatching.

Armyworm larvae are variable in color but are usually dark green or gray with three thick stripes along each side. First instar larvae move by looping their bodies, whereas the older larvae do not.

DAMAGE

Cutworm and armyworm larvae feed mainly on leaves and crowns but may clip off seed heads or may cut off plants near or below the soil surface. Damage is usually limited to certain parts of a field and may reoccur each season in the same place. Cutworms are active year round in the low deserts but are damaging to bermudagrass seed production from mid-March to October. The larvae feed at night and hide in the thatch layer or in a burrow in the soil during the day. Look for close clipping of grass around aeration holes, which are commonly occupied by larvae. Damage appears as circular spots of dead grass or depressed spots.

MANAGEMENT

Cultural practices and biological controls sometimes limit armyworm and cutworm populations. If sprays are necessary, consider spot treatments in areas of localized damage.

Biological Control
Larvae are parasitized by braconid wasps (Apanteles spp.) and by tachinid flies. Birds also commonly feed on cutworms, especially during irrigations. Bacillus thuringiensis subsp. kurstaki is a bacterium commercially formulated for caterpillar control. It is only effective against first- and second-instar cutworm larvae.

Cultural Control
Practice good weed control in and around the field and burn or remove straw and field trash from previous cuttings to reduce egg and worm overwintering sites.

Monitoring and Treatment Decisions
Look for damage symptoms and confirm the presence of cutworms by digging into the soil an inch or so around a damaged spear. Begin applications when insects first appear.

Common name Amount/Acre R.E.I.+ P.H.I.+
(trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
When choosing a pesticide consider information relating to the impact on natural enemies and honey bees and the environment. Not all registered pesticides are listed. Always read label of product being used.
 
A. BACILLUS THURINGIENSIS ssp. KURSTAKI
(various products) Label rates 4 0
MODE OF ACTION GROUP NUMBER1: 11
COMMENTS: Apply when cutworms are small, usually in the first or second instar.
   
B. ZETA-CYPERMETHRIN*
(Mustang) 3-4.3 oz 12 7
(Mustang Max) 3.2-4 oz 12 7
MODE OF ACTION GROUP NUMBER1: 3
COMMENTS: Efficacy trials pending, but experience with similar products has shown pyrethrins to be effective.
         
C. CYFLUTHRIN*
(Baythroid XL) 1.6-1.9 oz 12 0
MODE OF ACTION GROUP NUMBER1: 3
COMMENTS: Efficacy trials pending, but experience with similar products has shown pyrethrins to be effective.
   
+ Restricted entry interval (R.E.I.) is the number of hours from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of the two intervals is the minimum time that must elapse before harvest.
* 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/.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Bermudagrass Seed Production
UC ANR Publication 3472
Insects and Mites
E. T. Natwick, UC Cooperative Extension, Imperial County
M. D. Rethwisch, UC Cooperative Extension, Riverside County

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