Fall Armyworm Distribution and Population Dynamics in the Southeastern States

Following the winters of 1983-85, fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith), populations in the continental United States were restricted to extreme south Florida. Reinvasion of northerly areas occurred predictably each year with larval infestations on whorl-stage corn in southwest Georgia by mid- to late April each year. Pheromone trap catches indicated populations at Dade and Palm Beach Counties, FL, were greater and peaked earlier than those at more northerly locations during the early spring, indicating this area as either a major contributor or recipient of migrant FAW. Initial trap captures of FAW males occurred earlier and higher larval infestations were observed at Baldwin County, AL, than in locations in south Georgia. The proximity of weather systems inducing southerly wind components in areas ahead of the front were associated with initial trap captures of FAW males at northerly locations in all three years. Pheromone trap captures indicated FAW populations were lower in 1984 than in 1983 or 1985, probably because of the colder winter and spring temperatures recorded in 1983 and 1984, respectively. Severe outbreaks of FAW did not occur during the study although severe winters occurred each year. These data indicate that the conditions following extremely low winter temperatures may influence FAW populations more than extreme low temperatures alone. The (a)synchrony of emerging FAW adults at overwintering sites timed with the availability and amounts of susceptible stages of corn planted in more northerly areas may be the most important factors determining the magnitude of FAW populations each year throughout the southeastern states.