Chelonus insularis Cresson also parasitize the immature stages of the beet armyworm. A polyhedrosis virus sometimes causes epizootics in beet armyworm populations that causes virtually 100 percent mortality in some fields. The beet armyworm is difficult to control with chemicals because the young larvae web leaves together and feed under the webbing that protects them from insecticides. Older larvae are more tolerant of pesticides. In addition, some beet armyworm populations have acquired resistance to methomyl and perhaps other pesticides.
Pheromone traps can help monitor for moth flight activity.
All Bacillus thuringiensis strains are not necessarily acutely toxic to beet armyworms, but some strains do cause significant mortality and stunt the development of surviving caterpillars. The use of bacterial pesticides may help delay the acquisition of resistance to pesticides by the beet armyworm. For specific chemical control recommendations, consult the current Cooperative Extension Service publications on ornamental plant pest management.