Modeling black cutworm—Parasitoid—Weed interactions in reduced tillage corn

Abstract

Computer simulations were used to evaluate the impact of tillage upon black cutworm, Agrotis ipsilon (Hufnagel), damage to seedling corn through its effects on cutworm infestation, feeding and parasitism by Meteorus rubens (Nees von Esenbeck). Using 1982 conditions of Urbana, Illinois, simulated black cutworm infestations in no-till fields approached the economic threshold of two larvae per 100 corn seedlings. In disked and conventionally tilled fields, infestations were 30 and 75% less, respectively, because weeds for oviposition sites were less abundant before planting. Cutworm damage in notill equalled or exceeded the economic injury level of 3% yield reduction. In conventional tillage, damage was 75% less than in no-till due to decreased infestation. Although infestation in disked fields was more than double that in conventional fields, damage was similar because of preferential cutworm feeding on weeds. These simulated values for black cutworm infestation and damage were similar to field data obtained under comparable conditions of tillage and moth trap-captures. Predicted M. rubens density in no-till and conventional tillage ranged from ca. 4 to 22 per 100 corn seedlings, and black cutworm parasitism ranged from 26 to 75%. In disked fields, parasitoid density increased by 40% and parasitism increased slightly (33–80%) as a consequence of weed availability for floral nutrition after planting. Simulated values for parasitoid search efficiency were similar to those estimated from field data. The increased M. rubens density and parasitism in disked fields did not affect black cutworm damage substantially. Damage reduction due to parasitism ranged from 10 to 30% under all three tillage conditions. These simulations suggest that M. rubens—weed interactions are of minor importance compared to black cutworm—weed interactions in influencing cutworm damage. In addition, they indicate that preferential cutworm feeding on weeds can substantially offset preferential cutworm oviposition in weedy, reduced-tillage fields.