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Armyworms

The fall armyworm (Spodotera frugiperda) is the caterpillar species most commonly associated with foliar damage seen on turfgrasses, such as bermudagrass (Cynodon dactylon) and tall fescue (Festuca arundinacea) and home landscapes in South Carolina. Often noticed in late summer, these highly destructive caterpillars crawl through once pleasantly green areas, and in just a few hours, turn them into brown wastelands.

Adult moths, which may be attracted by bright lighting, will lay up to 1,000 eggs in a single night. They lay eggs in areas near desirable food sources, often on grass blades or upright structures, such as fenceposts and house siding. Upon hatching, the larvae spin silken threads, which aid in dispersing them from structures, and they immediately begin feeding. Minimal damage may be observed during early development. However, after the 4th larval state, over 93% of foliage consumption occurs. By the 6th stage of development, the larvae will burrow into the thatch and soil layer, where they will pupate and emerge as adults 10 to 20 days later.

Armyworms (Spodoptera spp.) can be easily identified in larval stages by the inverted “Y” shape on their heads. Adam Gore ©2021, Clemson Extension

Armyworms (Spodoptera spp.) can be easily identified in larval stages by the inverted “Y” shape on their heads.
Adam Gore ©2021, Clemson Extension

Armyworms (Spodoptera spp.) can reach up to 1½ inches in length during the larval stages. Adam Gore ©2021, Clemson Extension

Armyworms (Spodoptera spp.) can reach up to 1½ inches in length during the larval stages.
Adam Gore ©2021, Clemson Extension

In South Carolina, the peak of the armyworm developmental season typically takes place during the summer months. The entire life cycle of a fall armyworm can be completed in a single month with the potential for three or more generations to occur in a single year. The presence of armyworms in South Carolina generally depends on population explosions from southern states located around the Gulf of Mexico, where the climate is favorable for these insects to overwinter.

Identification

Fall armyworm moths are primarily gray in color with white markings and normally have a drop-shaped mark in the middle of the forewing. Adults may be up to 1 inch in length with a wingspan reaching 1½ inches. Larval stages range in color from green and yellow to brown and grey and can reach 1½ inches in length. The distinguishing characteristic of larvae is the presence of a yellow to white upside-down ‘Y’ shape on the head. Egg masses are white to cream in color and normally have a furry or moldy appearance, with eggs darkening in color over time.

Damage

In landscapes, initial damage from early instars (developmental stages of larva) may resemble drought or wilting symptoms in turfgrass, with later instar damage leaving a scorched or scalped appearance as most green foliage is consumed, leaving only grass stems.

During the early morning or late evening hours, several armyworms can be seen feeding or moving in large numbers hence the “army” reference in their common name.

Armyworms (Spodoptera spp.) can be found feeding during early mornings and late afternoons. Bert McCarty ©2021, Clemson University

Armyworms (Spodoptera spp.) can be found feeding during early mornings and late afternoons.
Bert McCarty ©2021, Clemson University

Armyworms (Spodoptera spp.) feed on turfgrass foliage, causing it to have the appearance of suffering from drought or scalping damage. Bert McCarty ©2021, Clemson University

Armyworms (Spodoptera spp.) feed on turfgrass foliage, causing it to have the appearance of suffering from drought or scalping damage.
Bert McCarty ©2021, Clemson University

Control

When damage is observed, the use of insecticides containing active ingredients, such as bifenthrin, Bacillus thuringiensis (B.t), cyfluthrin, cypermethrin, lambda-cyhalothin, permethrin, or spinosad, are viable options for control. When using contact insecticides, remember to avoid any irrigation or rainfall within 24 hours of application to allow for the maximum amount of time for impact on the armyworms. See Table 1 for examples of products containing these products.

Remember to read and follow all handling and applications directions as found on the label of each pesticide.

Insecticide Examples of Brand Names & Products
Bifenthrin Ferti-lome Broad Spectrum Insecticide Concentrate; & RTS1
Hi-Yield Bug Blaster Bifenthrin 2.4 Concentrate
Monterey Mite & Insect Control Concentrate
Ortho Outdoor Insect Killer Concentrate
Ortho BugClear Insect Killer for Lawns & Landscapes Concentrate; & RTS1
Up-Star Gold Insecticide Concentrate
Bifen I/T Concentrate
Talstar P Concentrate
Bacillus thuringiensis (B.t) Bonide Thuricide Bt Concentrate
Monterey Bt (concentrate); & RTU2
Natural Guard Caterpillar Killer Spray with Bt Concentrate; & RTU2
Safer Caterpillar Killer with Bt Concentrate
Southern Ag Thuricide Bt Caterpillar Control Concentrate
Cyfluthrin Bayer BioAdvanced 24 Hour Lawn Insect Killer RTS1
Bayer BioAdvanced Complete Insect Killer for Soil & Turf I RTS1
Bayer BioAdvanced Insect Killer for Lawns RTS1
Bayer Advanced Rose & Flower Insect Killer RTU2
Cypermethrin GardenTech Sevin Insect Killer Concentrate; & RTS1
Gordon’s Bug-No-More Lawn & Garden Insect Control Concentrate
Lambda-cyhalothrin Spectracide Triazicide Insect Killer for Lawns & Landscapes Concentrate; & RTS1
Martin’s Cyonara Lawn & Garden Concentrate; & RTS1
Martin’s Cyzmic CS Controlled Release Insecticide
Cutter Backyard Bug Control Spray Concentrate RTS1
Permethrin Bonide Total Pest Control Outdoor Concentrate
Bonide Eight Yard & Garden RTS1
Bonide Eight Garden & Home Insect Control RTU2
Hi-Yield Indoor/Outdoor Broad Use Insecticide Concentrate
Hi-Yield Lawn Garden Pet & Livestock Insect Control Concentrate
Southern Ag Permetrol Lawn & Garden Insecticide Concentrate
Tiger Brand Super 10 Concentrate
Spinosad Bonide Captain Jack’s Deadbug Brew Concentrate; & Conserve RTS1; & RTU2
SC Turf Ornamental Concentrate
Ferti-lome Borer, Bagworm & Leafminer Spray Concentrate
Monterey Garden Insect Spray Concentrate
Natural Guard Landscape & Garden Insecticide RTS1
Ortho Insect Killer Tree & Shrub Concentrate
Southern Ag Conserve Naturalyte Insect Control Concentrate
1 RTS = Ready to Spray (hose-end applicator)

2 RTU = Ready to Use (pre-mixed spray bottle)

Sources:

  1. Niemczyk, H. D., and David J. Shetlar. Destructive Turf Insects. H.D.N. Books, 2000.

If this document didn’t answer your questions, please contact HGIC at hgic@clemson.edu or 1-888-656-9988.

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