Written by 5:25 pm Lawn Tips

Fall Armyworms

Armyworms have gotten a lot of attention lately. The Fall Armyworm (FAW) is a caterpillar species and particularly difficult pest that eats and destroys over 80 different types of crops, as well as different grasses and landscapes. As adult moths, they can lay up to 1,000 eggs over night! The larvae are placed near a desirable food source, such as crops or green grasses. Once the eggs hatch, the larvae get to work feeding on the nearest resource as they move through different life stages. The 4th larval stage is the most destructive.

In areas where conditions are ideal for fall armyworms, infestations cycle continuously throughout the year. These areas tend to be the warmer, southeastern states. Outside of these areas, the FAW migrate when the weather is favorable and breed as little as one generation before they are gone. For most of the Eastern US, the FAW migrates in the summer in this fashion.

Armyworm Life Cycle

Egg Stage

The FAW life cycle is around 30 to 90 days, depending on the season. It is much longer in the winter months, ranging around 85 days. In the Spring and Fall, the caterpillars complete their cycle in around 60 days. Summer is their fastest life cycle, finishing in just around 30 days. As mentioned earlier, FAW can have several generations born across a single season depending on the climate. For this reason, you can see multiple generations born in the summer months or in areas of the south with warmer temperatures. Regional climate differences are also a driver of the length of life cycles. For example, armyworms in northern states have a longer life cycle than temperate southern states.

The first stage of the life cycle is the egg stages. At the beginning of this interval, female moths lay between 1500 to 2000 eggs, attaching them to surrounding foliage. She may even layer the eggs with a small number of grayish scales, which makes the eggs look moldy or fuzzy. The egg stage is short, only lasting up to three days in the summer.

Instars

The FAW has 6 instars (time frames between molting as the insect develops). As the young larvae grow, they will go from lengths of 1.7 mm all the way up to 34.2 mm. They grow their signature black spots along their green body. This later serves to camouflage among plants later in life. Another distinguishing characteristic is the upside down, yellowish “Y” on their heads. This stage occurs from anywhere between 14 to 30 days.

Pupa

The pupation of the Fall Armyworm typically happens down in the soil. At this point, the larva will make a loose oval shaped cocoon, about 25 mm in length. They use silk to bind together pieces of soil for their cocoon. In some cases, the soil may be too hard for this purpose and the larvae will use loose leaves or other nearby debris as a substitute. The FAW cannot handle long periods of cold weather at this stage of development.

Adult

The pupa emerges as an adult moth with a wingspan of up to 40 mm. Males and females can are differentiated by their forewing coloring. Males display gray and brown forewings with white spots at the tip and center of the wing. Females are harder to distinguish. Their coloring ranges from a full grayish brown across the entire wing to a speckling of grey and brown throughout. Adult FAW are nocturnal and most active during warm evenings with ample humidity.

Armyworm Damage

The adult moths lay their eggs on fenceposts near food sources and as larvae grow, they eat the surrounding vegetation. Their fast growth, large population and voracious appetite make them extremely destructive. By the end of their juvenile life stages, they will burrow through the soil where they will emerge as adults around two weeks later.

One of the toughest issues with Fall Armyworms is their wide range of host plants that they enjoy. Scientists have recorded over 80 different plants used as host spaces, but there seems to be a clear preference for grasses. Most recorded plants include sorghum, Bermudagrass, grass weeds, field corn, and sweet corn.

Unfortunately, many field and garden crops can fall victim to the FAW invasions, including beans, broccoli, cabbage, cotton, okra, sunflower, corn, oat, peanut, rice, sugarbeet, soybean, and more. Some fruits may also suffer damage, such as apple, grape, papaya, peach, and oranges. Current research suggests that there may be specific strains of fall armyworms that prefer a small group of host plants.

Damage Determination

For grassland, you may notice browning or wilting symptoms during the beginning stages of development. Later instars bring balding spots or a scorched look to your grass. The FAW eats the upper blades of grass, leaving behind the stems. These thin areas are prime locations for nuisance weeds to develop.

Vegetation or crops will suffer from holes and chewed leaves on crops. When plants are young, FAW larvae will chew small round pinhole looking damage as they cannot yet chew through the entire leaf. Older plants will show scattered and elongated window panes of damage. As the caterpillars come to the later developmental stages, holes will get larger and eventually break completely through green leafy vegetation.

Fall Armyworm Pest Control

Once an infestation has been identified, pesticides are the quickest and most effective way to eliminate the pest and mitigate the damage. Treating armyworms in the garden can be difficult. Control options are limited and outside of the scope of this article. However, treating armyworms in your lawn is easy. Early detection is key to limit the long-term impacts of this nuisance insect.

Early signs of armyworms will appear like the grass is suffering from drought damage. Early wilting or browning will turn to a scorched or scalped appearance if left untreated. This will differ from other pests, as only stems will remain in affected areas. In bad infestations, “armies” of armyworms can be seen feeding on a lawn in the morning and evening hours.

Armyworm Pesticide Recommendation

The pesticide bifenthrin has been around since the mid-1980s and has been a choice for millions of professionals and homeowners. Talstar P (Pro) Insecticide is a top choice recommended by professionals. This product is low odor and won’t cause plant burn where applied. Best of all, not only does Talstar P eliminate armyworm infestations, it also is effective on 75 common household pests inside and out. It will also remain effective for months after application. This product comes in a concentrate and must be mixed with water in a spray tank.

If you do not have a spray tank, Hi-Yield Bug Blaster Bifenthrin 2.4 RTS is a ready to use product that only requires a water hose. All you must do is shake well to mix, connect to your water hose and spray on your yard. The nozzle and bottle will appropriately dilute the product as you spray. One quart size bottle will treat up to 10,600 square feet of yard.

When treating your lawn with any product, make sure there is adequate time for it to dry before allowing pets or children onto the lawn. In addition, rain before drying could impact the effectiveness of the product. It is important to read the manufacturer label before applying.

After you have eliminated the infestation, repair the damage and thin spots to prevent weeds from moving in. Also, be sure to continue to appropriately water and mow your lawn to keep it healthy and help build natural resiliency from future pests.

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