Damage evaluation of armyworm to corn culture based on monitoring in attacked plants in three growing seasons

Abstract

The fall armyworm Spodoptera frugiperda is the main insect pest of corn in Brazil, with potential to cause significant losses in productivity. The objective of this study was to quantify the damage caused by insects to maize grown in different periods in three consecutive seasons, as well as monitor the presence of adults using synthetic sex pheromone in order to make the control based on monitoring. Experiments were conducted in 2007/2008, 2008/2009 and 2009/2010, in a randomized block design, using the cultivar AG 5011 in plots consisting of six rows of plants (5m x 0,70 m). Two types of treatments were compared in each growing season, with four replicates: 1) treatment with chemi- cal insecticides when 10 % of the corn plants were attacked, 2) without chemical treatment (control). In three seasons in any growing season, there was no significant difference between the percentage of plants attacked by caterpillars in plots treated with insecticide and control plots. Only in the 2009/2010 season were detected significant differences between corn yield of plots treated with insecticides and productivity of the control plots. This result, however, can not be attributed to insect attack, because the rate of infestation was similar in plants inherent to both types of treatment. In the 2008/2009 season were significant differences between the periods of growing corn on the percentage of plants attacked and productivity in control plots. In these plots, there was a trend of increased insect infestation and reduction in corn yield, with the advance of the sowing season. The monitoring of moths of S. frugiperda using synthetic sex pheromone has become possible to detect the presence of the insect in the experimental area in three seasons. It was considered that the results of the experiments did not coincide in all three seasons so it is necessary to continue their studies, improving the methodology, primarily determining a most appropriate time to control the insect before it reached the rate of 10 % of plants infested.