Livestock and hay producers should be scouting their pastures and hay meadows for fall armyworms. Armyworm infestations can wreak havoc on lawns, hay fields, pastures, and newly planted fall forages so scout these areas close and often. Armyworms were reported in Conway and Faulkner counties this past week. Producers should be scouting fields for armyworms. The armyworms could wreak havoc on pastures and hayfields.
Fall armyworms do not overwinter in Arkansas instead the adult moths catch wind currents and gradually move into the state from the south and lay eggs. Fall armyworm damage can appear almost overnight. Infestations can be easily overlooked when the caterpillars are small and eating very little. Once caterpillars grow large and consume more grass, damage becomes apparent. Fall armyworm infestations can be expected from now through September.
Producers should carefully examine grass blades, stems and organic debris at plant base, and soil surface in a 1 sq. ft. area. It is best to take at least 10 random 1 sq. ft. samples across the pasture or hay meadow. Female fall armyworm moths prefer to lay eggs in areas of abundant growth, so be sure to include a few of these areas in your 10 samples. Also, make note of the size of the armyworms. Knowledge of their size will help producers make sound management decisions. A 1 sq. ft. sampling device made of stiff wire or PVC pipe will make the sampling process much easier. Remember, armyworm outbreaks often occur in waves about 30 days apart, indicating the need for routine scouting.
There are a few tips to remember about fall armyworms. First, do not treat when armyworms are tiny, however, get prepared. Several natural enemies such as parasites, predators and pathogens occur and can possibly eliminate or reduce populations in a short period of time. Many of you will remember a few years ago how the parasite, Cotesia marginiventris, showed up in large numbers and helped control fall armyworms in many fields. County agents and producers saw the small white cocoon cases (of the pupal stage) that were mistakenly thought by some to be armyworm eggs. We have seen on several occasions that population numbers will often decrease after a population of small larvae had previously been observed. Secondly, the fall armyworm has about 6 larval instars. The last few and particularly the fifth and sixth instars are when most of the damage to pastures occurs. Of the total foliage consumed, greater than 80–85 percent will occur at these stages. The best advice is to not get over-anxious and treat before necessary. Likewise, do not wait until they become too large. Harvesting an infested hay meadow is an option if the hay is mature. Most of the products recommended will work well on medium-sized larvae. Unlike cotton, corn or other crops the larvae have no place to avoid the insecticide and are easier to kill in pasture situations.
The treatment threshold for fall armyworms is 3 or more worms per square foot. “2021 Insecticide Recommendations for Arkansas MP-144” lists insecticides that can be used against fall armyworms in pastures and home lawns https://www.uaex.uada.edu/publications/mp-144.aspx.
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