How to Manage Pests

UC Pest Management Guidelines

Floriculture and Ornamental Nurseries

Armyworms and Cutworms

Scientific names:
Beet armyworm: Spodoptera exigua
Yellowstriped armyworm: Spodoptera ornithigalli
Variegated cutworm: Peridroma saucia

(Reviewed 3/09, updated 6/10)

In this Guideline:


DESCRIPTIONS OF THE PESTS

Beet armyworm

Beet armyworm is the most frequently encountered of the three species listed above. Adults are heavy bodied moths (wingspread is about 1 inch, or 25–28 mm) with a characteristic mustard or orange colored liver-shaped spot on the forewings that is narrowly ringed with white. The female lays egg masses on the undersides of leaves, covering the eggs with felt made from her body hairs. The first through third instar larvae often feed gregariously, skeletonizing the undersides of leaves, or they feed on the insides of buds. Later instar larvae disperse and feed individually, chewing entirely through leaves or flowers. Early instar larvae are small and green, while late instar larval color may be green, brown, black, or gray. In all instars, there are fine lines along the length of the body, with a more conspicuous lateral stripe and a black spot just dorsal to the lateral stripe behind the head.

Beet armyworm continually develops during winter in mild areas and builds up on weeds and in cotton, lettuce, and tomato fields. One generation can take as little as 31 days at 75°F or 24 days at 80°F. Egg to adult generation times can be calculated using degree-days (DD) based on a lower developmental temperature of 54°F. The egg stage requires the accumulation of about 94 DD from the time they are first laid until egg hatch. The larval and pupal stages require the accumulation of 470 DD and 318 DD respectively for females and 540 DD and 344 DD for males.

Yellowstriped armyworm

The yellowstriped armyworm larvae have a pair of black triangles on the back of most segments. Some larvae appear nearly completely black when viewed from above. The lateral stripe is bright orange or yellow. The adult has a complex and highly contrasting pattern of brown, yellow, and white on the front wings, and wingspread measure about 1.5 inches.

Variegated cutworm

The variegated cutworm overwinters as a naked pupa in the soil. Adults have a distinct liver-shaped outline on the front wings and their wingspread can measure from 1.5 inches to a little over 2 inches. Larvae have yellow or orange spots or a broken longitudinal stripe at the top of the body, which is otherwise gray. Often there is a dark triangle or W-shaped mark on the top of the eighth body segment.

DAMAGE

Armyworms and cutworms mostly are a concern because they directly damage flowers as well as leaves that would normally be marketed with the flowers. Presence of late-instar larvae in seedling flats can also cause tremendous plant loss. On the other hand, moderate early-season feeding by armyworms on gypsophila may actually increase tillering and yields.

MANAGEMENT

Biological Control

A number of parasites, both tachinid flies and parasitic wasps, attack Lepidoptera larvae and reduce their population growth rate. However, even if armyworm or cutworm larvae are parasitized, they continue feeding through to the last instar and still damage crops. Viruses also do not usually kill the larvae until later instars. Applying insecticides other than Bacillus thuringiensis (Bt) products are likely to exclude parasites because their residues are lethal to these beneficial insects. For more information, see BIOLOGICAL CONTROL.

Cultural Control

Because these pests feed on a large variety of plant species, keep production areas free of weeds, many of which serve as hosts to armyworms and cutworms . Exclusion of winged adults can be accomplished by covering openings to the greenhouses with screens. Screens are especially important when lights are used at night in greenhouses to control flowering because lights attract moths. Individual seedling flats may also be covered with screens to exclude adults and larvae. Row covers can be a practical measure to exclude moths in field production as long as the mesh prevents entry of adults and the row cover is held above the plant surface to eliminate oviposition (egg laying) through the fabric.

Monitoring and Treatment Decisions

If Bt sprays are planned, use pheromone traps to determine adult flight activity and mating. Once adults are caught in traps, it is very likely that larvae are present and Bt should be applied as soon as possible because it is most effective against young larvae. Use regular visual inspections of plants to detect larvae and their damage.For guidelines on when to treat, see ESTABLISHING TREATMENT THRESHOLDS.

TREATMENT

Selected Materials Registered for Use on Greenhouse or Nursery Ornamentals

Read and follow the instructions on the label before using any pesticide. Before using a pesticide for the first time or on a new crop or cultivar, treat a few plants and check for phytotoxicity. Also consider pesticide resistance management and environmental impact.

Class   Pesticide
(trade name)
Manufacturer R.E.I.1 Mode of action2 Comments
  Calculate impact of pesticide on air quality
biological A. Bacillus thuringiensis
ssp. kurstaki#
(various products)
Valent 4 11 Most effective against early instar larvae; pheromone trapping recommended for timing applications.
botanical A. pyrethrin/PBO3
(PT Pyrethrum TR)
Whitmire MicroGen 12 3/— An aerosol.
B. pyrethrin/rotenone
(Pyrellin EC)
Webb Wright 12 3/21B  
carbamate A. carbaryl* Bayer 12 1A  
insect growth regulator A. azadirachtin
(Azatin) XL
OHP 4 un Must contact insect. Repeat applications as necessary. Label permits low-volume application.
B. diflubenzuron
(Adept 25WP)
Chemtura 12 15  
C. novaluron
(Pedestal)
Chemtura 12 15 Use no more than twice per year and don"t exceed 52 oz/acre/year. Don"t use on poinsettia.
D. tebufenozide
(Mimic)
Dow Agro
Sciences
4 18  
organophosphate A. acephate
(Orthene T, T&O Spray)
Valent 24 1B A number of chrysanthemum varieties have exhibited phytotoxic reactions. In greenhouse only labeled for greenhouse use on anthurium, cacti, carnation, rose, orchids, some foliage plants, young poinsettia, and some varieties of chrysanthemum. Can stunt new growth in roses.
B. acephate
(PT 1300 Orthene TR)
Whitmire MicroGen 24 1B An aerosol only for greenhouse use.
C. chlorpyrifos*
(PT DuraGuard ME)
Whitmire MicroGen 24 1B  
organophosphate/
pyrethroid
A. chloropyrifos/ cyfluthrin*
(Duraplex TR)
Whitmire MicroGen 24 1B An aerosol.
pyrethroid A. bifenthrin
(Attain TR)
Whitmire MicroGen 12 3 Check label. A fogger for greenhouse use only.
B. bifenthrin*
(Talstar Professional)
FMC 12 3 Label permits low-volume application.
C. cyfluthrin
(Decathlon 20WP)
OHP 12 3 Label permits low-volume application.
D. deltamethrin*
(DeltaGard)
Bayer 12 3  
E. fenpropathrin*
(Tame 2.4EC Spray)
Valent 24 3 Label permits low-volume application.
pyrethroid F. fluvalinate
(Mavrik Aquaflow)
Wellmark 12 3 Label permits low-volume application. Also labeled as a cutting dip at 5 fl oz/100 gal.
G. permethrin
(Astro)
FMC 12 3 Direct application to blooms may cause browning of petals. Marginal leaf burn may occur on salvia, diffenbachia, and pteris fern. Label permits low-volume application. Do not apply more than 2 lb a.i./acre/year.
spinosyn A. spinosad
(Conserve SC)
Dow Agro
Sciences
4 5 Do not apply more than 10 times in a 12-month period. Compatible with most beneficials, but highly toxic to bees and hymenopteran parasites. Direct contact can cause significant mortality to Phytoseiulus persimilis.
1  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.
2 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/.
3 PBO = piperonyl butoxide
# Acceptable for use on organically grown ornamentals.
* Restricted use material. Permit required for purchase or use.

IMPORTANT LINKS

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Floriculture and Ornamental Nurseries
UC ANR Publication 3392

Insects and Mites

  • J. A. Bethke, Entomology, UC Riverside
Acknowledgment for contributions to Insects and Mites
  • K. L. Robb, UC Cooperative Extension, San Diego County
  • H. S. Costa, Entomology, UC Riverside
  • R. S. Cowles, Connecticut Agricultural Experiment Station, Windsor, CT
  • M. P. Parrella, Entomology, UC Davis

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