Green Cane Harvest Effect on Pseudaletia unipuncta (Haworth) (Lepidoptera: Noctuidae) Larvae Abundance and Losses Caused by This Pest in Tucumán, Argentina

Abstract

From 2010 to 2012 harvest seasons, studies of the armyworm Pseudaletia unipuncta were conducted in sugarcane in Tucumán. The larvae are nocturnal and during the day remain hidden under the crop residues or in the soil. Damage begins in spring when temperature rises. They produce damage by feeding and killing the shoots, delaying the growth of the new shoots in the cane field. This study aimed to evaluate the effect of agricultural residues of sugarcane green harvest on larval abundance and the losses caused by this armyworm. Trials were conducted at three locations. Twelve points of 2 m row length were evaluated every 15 days from September to November. The number of larvae and percentage of affected shoots were evaluated. When the attack of P. unipuncta began in September, a plot of 1 ha was sprayed with pesticides, and another plot was left with harvest residues and the pest. Five samples of 10 stalks were extracted per plot. Factory parameters (pol, brix) were evaluated in the lab. Localities averaged shoot losses between 13 and 30 %. The average relative abundance of larvae in the plots with harvest residues was 0.5 larvae per 2 m row; no larvae were found in plots without residues. Factory sugar yield was 10.7 % in the plot without insecticidal control and 12 % in the treated plot, with a total sugar loss of 23.2 % per ha. To prevent losses caused by this species, it is important to sample early green cane harvested fields in spring.