Brazil
August 6, 2024

Fall armyworm on signal grass - Photo: Simone Mendes

A study by Embrapa Maize and Sorghum recommends fall armyworm (Spodoptera frugiperda) management practices that are adapted to integrated crop-livestock-forestry systems (ICLFS). These guidelines are based on the new scenario of corn farming, which involves intercropping with signal grasses. The techniques are recommended for pasture establishment and mulching in no-till farming systems and and they are the prerogatives of such models, which combine productivity with sustainability. 
 

Fall armyworm is one of the most worrying pests in integrated production systems, and its management must take into consideration efficient control practices, since the insect feeds on several plant species. In addition, S. frugiperda adapts fast to the main management strategies currently in use, namely the use of Bt crops (containing genes of the bacteria Bacillus thuringiensis) and chemical control.

“Managing fall armyworm in the field is complex and should consider the production system as a whole. That is why it is necessary to better understand its occurrence and permanence in systems like integrated crop-livestock-forestry and integrated crop-livestock ones (ICLFS and ICLS), which are getting more and more popular in different regions of Brazil”, the researcher Ivênio Oliveira comments.

The research warns farmers to be cautious when intercropping signal grass and corn, since this type of grass is one of the main plant hosts of fall armyworm. The aim is to help farmers understand S. frugiperda 's behavior and offer alternatives to manage it within integrated production systems. “Understanding the stages of monitoring and observing the right moments for control decision-making is the basis for Integrated Pest Management (IPM)”, Oliveira says.

It was observed that signal grass interferes in the system, favoring the increase of caterpillar population; however, there are adaptations  to management strategies that can diminish the problem. “The key is to understand how to apply the strategies and the decision-making levels”, the researcher adds. 
 

Integrated Pest Management is the most adequate solution for integrated systems

The study carried out by Embrapa Maize & Sorghum adopted Integrated Pest Management as a sustainable alternative to control corn fall armyworm. 

“Control strategies with different products were tested, observing the validation of decision-making indices to control the pest. The difference was that there was no recommendation for pest control in integrated production systems, and this study calls attention to this”, Oliveira observes. 

In the study, insecticide applications to control fall armyworm were conducted observing the following decision-making indices: level of economic damage (LED) and level of control (LC). The research points out that the pest population monitoring is essential so that applications are conducted only before LC is reached, which is before LED. The cost to control the insect cannot be higher than the damage caused by the pest attack.

In general, chemical control with insecticides is recommended when there is LC of 20% of scraped or punctured plants. “This percentage is detected either through samples made with pheromone traps or visually, based on the scale of damage caused by the worms”, the researcher explains. 

The experiments were performed in environments adapted to simulate commercial cultivation conditions, adopting plots with large dimensions to better express the effect of the different conditions and treatments.

“It was clear that, in the conditions this work was carried out, the parameters for decision-making on S. frugiperda control for corn cultivated in integrated crop-livestock and crop-livestock-forestry systems are different from the ones in monocultural systems, as the damages caused to the aerial parts of corn plants proved to be influenced by the presence of signal grass”, Oliveira highlights. 
 

According to the researcher, in the initial cultivation period, which lasts approximately up to the V5 growth stage, when only corn plants are present in the plantation area, the same conventional parameters of trap sampling or visual scales can be used. Therefore, decision-making for control is based on the average capture of three S. frugiperda adult moths per trap or 20% of attacked plants with damage scores that are higher than 3.

“Integrated Pest Management is more adequate than scheduled use of chemical insecticides. Bt bioinsecticide spraying must be carried out after the occurrence of damage grade up to 2, by visual sampling, which means the presence of caterpillars with less than 1 centimeter. As signal grass plants grow, they start to be part of the production area and also must be considered sampling units because it is possible that caterpillars migrate to corn plants and vice versa”, the researcher explains.

The experiments showed a possible increase of caterpillars per area unit and a higher pressure on corn plants of damage level 1, indicating the presence of smaller caterpillars.

The decision-making process in order to manage the pest is rather assertive with continuous sampling and use of pheromone-based traps, because of the difficulty of visual sampling in signal grass plants. “Integrated Pest Management to control this caterpillar in integrated systems reduces from four to three the use of insecticide application per corn harvest”, Oliveira concludes. 

Photos by: Simone Mendes and Sandra Brito (corn cobs in the field)

Website: http://www.embrapa.br

Published: October 24, 2024