Cover Story

Are Fall Armyworms Going to be a Problem this Year? Some Considerations for its Management in Turf.

By Alejandro Del-Pozo Ph.D., Tom Kuhar Ph.D. and Mike Goatley Ph.D.

Several of you witnessed or were impacted by the huge numbers of fall armyworms (Spodoptera frugiperda, FAW; Fig. 1) in the Mid- Atlantic U.S. in summer and fall 2021. The turf team at Virginia Tech was ‘inundated’ with pictures from landscaping companies and home owners showcasing brown patches in their lawns (Fig. 2). All those inquiries had one factor in common, the presence of FAW caterpillars in large numbers. It was one of the most devastating FAW infestations that we have seen in Virginia in many years.

Figure 1A: Fall armyworm, Spodoptera frugiperda Lepidoptera: Noctuidae, adult (photo by L. Buss).

Figure 1B: Fall armyworm, Spodoptera frugiperda Lepidoptera: Noctuidae, caterpillar (Photo 1B, photo by M. Rice)

Figure 1C: Adult moths have some characteristic white marks on the front wings, and immatures have an inverted “Y” suture on the front of their heads. Seen here are both late instar caterpillars and defoliation on affected turf (photo by T. Kuhar).

Fig. 2. Examples of heavily infested and damaged lawns by fall armyworms in two different locations in Virginia during late July early August 2021. Pictures provided by B. Mutgaas and K. Mathias.

Fig. 2. Examples of heavily infested and damaged lawns by fall armyworms in two different locations in Virginia during late July early August 2021. Pictures provided by B. Mutgaas and K. Mathias.

The big question right now is “what do we predict is going to happen in 2022?”. The short answer is that we have no idea. Last year’s FAW infestations were driven by a perfect storm of dry conditions in the deep south causing higher than usual population densities of the pest, coupled with summer storm fronts transporting large numbers of adult moths to more northern states. It is unlikely that all of those factors will line up again in 2022, but not impossible. We do know that FAW does not overwinter in Virginia and so there is no starting population leftover from last year. We encourage you to be on the alert that FAW could show up again. Below are some important considerations for its management:

1) Be aware of reports of adult FAW moth activity nearby your locality. Because it is too cold for these critters to spend the winter in Virginia, we frequently do not see this pest. However, storm systems in the summer can carry adults to northern latitudes. Thus, knowing that moths have been spotted is useful. We have been following the great work from Dr. Terri Billeisen at North Carolina State University, as she has been tracking the presence of these adults across North Carolina. You will find the latest map showing FAW presence in NC at https://ncturfbugs. wordpress.ncsu.edu/pest-tracking-maps/fall-armywormmap/ This information will give us an idea how close those adults are getting to Virginia. Our team is also deploying the same FAW pheromone bucket traps to monitor the presence of these moths across Virginia. Traps are going out now in mid-July and will be monitored into September. If you would like to know the status of this pest, please visit / subscribe the Virginia Ag Pest Advisory at https://blogs.ext.vt.edu/ag-pest-advisory/ to get the latest updates.

2) Know the vulnerability or susceptibility of your turf or other commodities. FAW is preferentially a grass feeder, but has some ‘additional’ preferences for specific types of grass. In 2021, it turned out that these caterpillars devoured tall fescue, Bermuda and Zoysia. However, last year they seemed to be ‘picky’ eaters, leaving behind ‘untouched’ crabgrass, orchardgrass, Kentucky bluegrass, nutsedge and stiltgrass. Although it varied across the state, some alfalfa fields were even damaged in some parts of Virginia. Surprisingly, corn (a known host plant) appeared to be untouched by FAW in Virginia last year. Different strains of FAW have different host preferences. Know what types of grass you are managing, and be on the lookout for caterpillars if you are working with the highly preferred grass types (such as fescues). These lawns will require some additional attention to decide when to spray if adults are flying in your area. If FAW does appear again, note what grass types seem to be getting infested. Talk to others. Early communication is critical, and we plan to do our part by disseminating timely information.

3) Chemical control. Pyrethroid insecticides are a cheap and effective option to quickly ‘knockdown’ the number of caterpillars. Several products, including Talstar (bifenthrin), or Scimitar (lambda-cyhalothrin) have shown at both in laboratory and under field conditions high efficacy to control these caterpillars (see Figs. 3 and 4). Diamides are another effective insecticide option to control FAW caterpillars in turf. Products such as Acelepryn (chlorantraniliprole) or Mainspring (cyantraniliprole) significantly reduced the percentage of defoliation and the number of caterpillars after treatments were applied under laboratory and field conditions as well (Figs. 3 and 4). Provaunt (indoxacarb) and Matchpoint (spinosad) are also effective on FAW. Based on observations in 2021, spring or summer preventative applications of diamides such as Acelepryn, targeting white grubs, provided effective control against FAW. Keep in mind that preventative applications of neonicotinoids like Merit (imidacloprid) and others for white grubs will not control FAW.

Fig. 3. Percent defoliation of mid-size fall armyworm caterpillars from laboratory bioassays using tall fescue in 2022. Selected products are presented on the X-axis, and were used at the maximum label rate. The panel on the left summarizes data from one day after treatment (1 DAT), and right panel, data for 3 DAT. Different letters on top of bars represent statistical differences among products.

Fig. 4. Number of fall armyworm caterpillars per squared foot (Y-axis) 7 days after the application of several insecticides (X-axis), using the maximum label rate in turf in 2019. Different letters on top of bars represent statistical differences among products.