How to Manage Pests

UC Pest Management Guidelines

DESCRIPTION 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. (To calculate degree-days, see "Degree-days" on the UC IPM Web site.) 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. Degree-day calculator    Degree-day table

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.

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.

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.

MON ITORING and WHEN TO TREAT

Use pheromone traps to determine adult flight activity and mating. This information can be used to time Bt sprays for young (susceptible) larvae. Use regular visual inspections of plants to detect larvae and their damage.

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.

PUBLICATION

UC IPM Pest Management Guidelines: Floriculture and Ornamental Nurseries
UC ANR Publication 3392
Insects and Mites
K. L. Robb, UC Cooperative Extension, San Diego Co.
H. S. Costa, Entomology, UC Riverside
J. A. Bethke, Entomology, UC Riverside
M. P. Parrella, Entomology, UC Davis
Acknowledgment for contributions to the insects and mites section:
R. S. Cowles, Connecticut Agricultural Experiment Station, Windsor, CT

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