Green cane harvest effect on Pseudaletia unipuncta (Haworth) (Lepidoptera: Noctuidae) larvae abundance and losses caused by this pest in Tucuman, Argentina

摘要

From 2010 to 2012 harvest seasons, studies of the army worm Pseudaletia unipuncta were conducted in sugarcane in Tucuman. The larvae are nocturnal and, during the day, remain hidden under the crop residues or in the soil. Damage begins to be noticed in spring when the temperature rises. They produce damage by feeding and killing the shoots, after which new shoots are produced, but this delays the growth of the cane field. This study aimed to evaluate the effect of agricultural residues of the sugarcane green harvest on larval abundance and the losses caused by this armyworm. The trials were conducted at Simoca, Fronterita and Louisiana. Twelve points of 2 metres row length were evaluated every 15 days from September to November. The number of larvae and percentage of affected shoots (counting the number of healthy and dead 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 stems 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 fields in spring giving special attention to early green cane harvested fields.