Sweet corn genotypes and ear insect infestations cultivated under different weed management regimes

Weed management is crucial in most cropping systems in part because of direct and indirect interactions of weeds as alternative hosts for pest species and food and shelter for natural enemies. The tested hypothesis was that weed management would affect insect pests’ infestation of different sweet corn genotypes, altering or modulating resistance. Five commercial sweet corn genotypes (GSS 41243, GSS 3969, GSS 41499, GSS 42072, and Tropical Plus) were cultivated during two growing seasons under clean weed (herbicide application) and reduced weed (grazed weeds between rows) management. Fall armyworm (Spodoptera frugiperda), corn earworm (Helicoverpa zea), and cornsilk fly (Euxesta sp.) infestation was surveyed for 7 and 13 sampling dates by counting the insects found on the plants during the 2015 and 2016 seasons, respectively. Sweet corn ears were also sampled on three different occasions in each season. The number of larvae of each species, the damage scores for the noctuids (corn earworm and fall armyworm), the number and percentage of damaged grains by the larvae infesting corn ears (cornsilk fly, corn earworm, and fall armyworm), and size, diameter, and length of ears with or without husks were assessed. Yellow sticky traps were used to determine the abundance of cornsilk fly adults on four and five different occasions in the 2015 and 2016 seasons. The genotypes GSS4199 and GSS3969 were less damaged by fall armyworm, corn earworm, and cornsilk fly, and these differences were observed when sweet corn genotypes were growing under clean weed management. Plant characteristics such as differences in ear length and diameter with and without husks negatively affected ear pests. There was a positive and significant correlation between cornsilk fly and fall armyworm and corn earworm’s occurrence, suggesting that infestations with corn earworms facilitate the infestation of cornsilk fly.