Fall Armyworm Control in Home Lawns, 2021

Encyclopedia Article

moth egg masses on golf course flag pole
Fall armyworm egg mass on golf course flag pole.  Photo by Rob Lindsay, Coldwater Golf Links, Ames IA

The fall armyworm, Spodoptera frugiperda, caused unprecedented infestation and destruction of turfgrass on golf courses and home lawns in the southeastern U.S. this summer. Severe ddamage was reported from Oklahoma to Georgia and Indiana to Maryland.

Multiple generations of fall armyworms in the South created enormous populations of moths that were blown into Iowa by storms in late August. The arriving female moths “dumped” their eggs where they landed and the tan-to-buff, fuzzy or furry egg masses containing 100 to 500 shiny, spherical eggs were found on trees, house siding, playground equipment, birdhouses, bird feeders, posts, poles, golf carts, etc.  See photo 1.  Egg masses can be removed by gently scraping, followed by brushing or scrubbing with soapy water.  Spraying insecticides on egg masses is not advised. 

Damage

By mid-September the egg masses had hatched, and large numbers of fall armyworm caterpillars were seen feeding in some lawns and causing noticeable damage.  Turfgrass damage has been widespread but spotty through the eastern 2/3 of Iowa.  Damage is worst in new seedings and plantings less than one year old and in turf-type tall fescue more than Kentucky bluegrass.

 Frank Peairs, Colorado State University, Bugwood.org
Early instar fall armyworm caterpillars are greenish in color.
Photo: Frank Peairs, Colorado State University, Bugwood.org

Scout lawns for armyworms by carefully inspecting the turfgrass.  Fall armyworms are surface feeders.  They may conceal in the heat of the day, but they live above ground and feed on the grass blades.  You will not need to dig in the soil to find them. Fall armyworms are tiny and green with a black head when they hatch, but they grow quickly and become darker with age.  Fully grown caterpillars are 1.5 to 2 inches in length and may be green, brown, or black with light stripes.  See photo 2.

Evaluate the turfgrass health and vigor, the size of the caterpillars, the amount of feeding damage, and the time till expected frost when determining if insecticide treatment is warranted.

Fall Armyworm Control Suggestions for Home Lawns

  • Carefully scout to determine the number, size, and distribution of fall armyworms and the condition of the turfgrass.
    • Small armyworms (greenish in color) are much easier to control than caterpillars nearing their full-grown length of 1.5 to 2 inches.
    • Spot treatment may provide early control without applying insecticide to the entire lawn. 
    • Healthy turfgrass may tolerate low to moderate amounts of damage and can recover with watering and fertilization.  See Recovery below.
  • Mow tall turfgrass before treatment to improve insecticide coverage. Collect the clippings that accumulate on the surface.
  • Irrigate lightly several hours before treatment to increase larval activity on the soil surface.
  • Apply insecticides early or late in the day, when fall armyworm larvae are most active
  • Most home lawn insecticide products containing pyrethroid, carbamate, or neonicotinoid active ingredients are labeled for armyworm or “caterpillar” control in residential lawns.  See Table 1.
    • Pyrethroid resistance has been reported in other parts of the country. If there is no quick control of fall armyworms after applying a pyrethroid, consider using a different class of insecticide, or hire a lawn care company to apply a chlorantraniliprole or tetraniliprole compound.
    • Azadirachtin insecticides (Neem oil) can provide control of small larvae and are certified organic.
  • Homeowner insecticides come as granules, ready-to-use sprays, or concentrates that require dilution with water before application.
  • Concentrate formulations require a tank sprayer and proper dilution of the product according to the label directions
  • Ensure adequate coverage and penetration of established turfgrass by spraying a minimum of 1 gallon of spray solution per 1,000 square feet.
  • Granules are easy to apply and may not require special application equipment.  Granule products require watering for activation and may be a bit slower-acting
  • Do not irrigate for 24 hours after a spray application.

Turfgrass Recovery

 Queensland Government, Australia
Caption

Recovery of damaged turfgrass is possible. The caterpillars will eat the leaf blades, and the expose the crown to environmental stress. Irrigate to supply regular moisture to keep the crown alive and allow the plant to recover. You can also add new seed to the area.  Fall is the best time to establish turfgrass.  After seeding, make sure to keep the area supplied with proper soil moisture. Finally, an application of fertilizer will provide nutrients to help the plants recover more quickly. Apply 0.75 to 1 lb. of a slow-release nitrogen source per 1,000 square feet to provide the needed nutrition to speed up recovery.

 

Example insecticides available to home owners for fall armyworm control.

Active Ingredient

Chemical Class

Formulation / Comments

Example Trade Names

Bacillus thuringiensis

Bacterial

RTU and Concentrate.

Small caterpillars only

Thuricide

bifenthrin

Pyrethroid

Granule, RTU and Concentrate

Ortho Bug-B-Gone Insect Killer

carbaryl

Carbamate

Granule, RTU and Concentrate

Sevin

chlorantraniliprole + bifenthrin

Diamide + Pyrethroid

Granule

Roundup® For Lawns Bug Destroyer

deltamethrin

Pyrethroid

Granule

Hi-Yield Turf Ranger Insect Control

gamma-cyhalothrin

Pyrethroid

Granule, RTU and Concentrate

Spectracide Triazicide Insect Killer

imidacloprid + cyfluthrin

Neonicotinoid + Pyrethroid

Granule, RTU and Concentrate

Bioadvanced Complete Insect Killer

permethrin

Pyrethroid

Granule, RTU and Concentrate

Hi-Yield 38 Plus Turf, Termite, and Ornamental, Eight

spinosad

Spinosyns

Granule, RTU and concentrate

Fertilome Borer, Bagworm, Tent Caterpillar, and Leafminer Spray

trichlorfon

Organophosphate

Granule

Bayer Advanced 24 Hour Grub Killer Plus

Last Reviewed: 
September, 2021
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