Timely Application of Four Insecticides to Control Corn Earworm and Fall Armyworm Larvae in Sweet Corn.

Angela M. Linares-Ramírez,Diego M. Viteri

doi:10.3390/insects13030278

Abstract

Simple SummaryCorn earworm and fall armyworm are the most important Lepidopteran pests in sweet corn worldwide. Timely application of insecticides during pollination is crucial to control both species and produce kernels with higher quality. Our results showed that applications of insecticides should be conducted at 48 h after pollination. Emamectin benzoate and chlorantraniliprole provided an adequate control of fall armyworm and corn earworm larvae. Furthermore, emamectin benzoate should be applied to larvae in later instars (fourth–sixth) while chlorantraniliprole and spinetoram should be sprayed when infestations of larvae in earlier instars (first–third) are observed.Insecticide sprays are a common practice to control corn earworm, Helicoverpa zea (Boddie), and fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), in corn (Zea mays L.) at reproductive stages. Our objectives were to determine (1) the most appropriate time for insecticide applications and (2) the effect of four insecticides on the survival of larvae as well as their weight. ß-cyfluthrin (0.4 mL/L), chlorantraniliprole (0.6 mL/L), emamectin benzoate (0.2 g/L), and spinetoram (1.5 mL/L) were sprayed on silks of sweet corn planted in Isabela and Lajas, Puerto Rico 3 h before and 24 and 48 h after pollination. The number of kernels produced and the damage of larvae on kernels were quantified at harvest. In addition, percentages of mortality and changes on larval weight were noted at 96 h after insecticide applications. Insecticide sprays at 3 h before pollination reduced the number of kernels or were similar to the control in all treatments. However, emamectin benzoate sprayed in Lajas and chlorantraniliprole applied in Isabela at 48 h after pollination increased the number of kernels (281–294) and reduced the damage of larvae on kernels (<0.5%) compared to the control (201–229; >7%). Furthermore, applications of emamectin benzoate caused higher percentages of fall armyworm larval mortality (>70%). Conversely, ß-cyfluthrin and chlorantraniliprole caused lower percentages of mortality (<30%) and only chlorantraniliprole and spinetoram reduced the weight of corn earworm and fall armyworm larvae collected in both locations. This information may help pest management programs and corn breeders to schedule insecticide sprays and pollination in the field.

Highlights

Insecticide applications at 3 h before pollination or 24 h after pollination reduced the number of kernels produced or were similar to the control, especially in lower corn earworm and fall armyworm infestations (Table 7)
Our data suggest that safe insecticide sprays on silks should be conducted at 48 h or longer after pollination
The extracellular surface of corn silks has lipids with non-polar molecules [24]. This hydrophobic property of the silks caused bubbles of water to form on the surface when insecticides were sprayed

Summary

Introduction

Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), and fall armyworm, Spodoptera frugiperda E. Smith) (Lepidoptera: Noctuidae), are the most important pests affecting field/sweet corn (Zea mays L.) in the tropics, the United States, and worldwide [1–6]. Larvae of fall armyworm feed on leaves, tassels, and kernels [7] while corn earworm larvae are mostly observed feeding on kernels or cob tissue at reproductive stages [4]. Later larval instars (fourth to sixth) cause higher damage in the plant tissue, and yield losses over 18%

Objectives

Methods

Results

Conclusion