Damage caused by fall armyworm and how to manage it

One of the most difficult pests to control, because of where it hides, is the fall armyworm.

10.06.2016 | 20:59 (UTC -3)

The damage caused by insects in corn crops worried Brazilian farmers in the 2013 harvest. Despite investments, in more than 70% of the total sown in transgenic corn in the last harvest (five harvests ago this percentage did not reach 15%), there were losses caused by caterpillars that significantly compromised crop productivity, with emphasis on the fall armyworm (spodopterafrugiperda).

In Brazil, the fall armyworm was considered a pest in the 60s due to the outbreak in corn, rice and pasture crops, and the control methods used by farmers at that time were not efficient. Since then, the difficulty in controlling the pest has become a routine, costing more than 600 million dollars in the 2009 Brazilian harvest. Currently, it is estimated that the fall armyworm is responsible for 25% of the damage caused by insects in crops of corn.

The emergence of transgenic corn hybrids has raised hopes of reducing fall armyworm problems. However, without adequate prevention, the risks of breaking resistance in the technology Bt It's tall. The planting of refuge areas with isogenic plants (not Bt) has been proposed as one of the main measures to reduce the growth rate of populations resistant to GMOs. This strategy aims to favor the reproduction of susceptible insects with possible resistant insects originating from the area Bt, generating susceptible populations.

Despite technical explanations about the reason for the refuge area, its effective use is still very low in Brazil. This situation can be justified due to the lack of clarity on how to conduct refuge areas, especially with regard to target pest control. However, it remains essential to carry out good agronomic practices and apply the precepts of integrated pest management (IPM) in any crop, which includes refuge areas. that GMOs still require the use of phytosanitary products, even if only in refuge areas.

On the other hand, insecticide applications to control fall armyworm have been inefficient, with insecticides previously used successfully now not showing the same effectiveness. However, this is sometimes due to the use of inadequate application techniques which, as they do not correctly reach the targets, favor the selection of individuals resistant to various classes of insecticides. This includes everything from inadequate dosages to the low quality of spray droplet distribution on crops.

It is essential to be aware that spraying can determine the action or not of proven efficient products. Therefore, knowledge of application technology becomes a vital ally for the farmer when chemical control of fall armyworm becomes necessary in crops.

A basic requirement to be effective in insecticide applications is the correct choice of spray tip models, also popularly called spray nozzles. These items are responsible for determining the size and distribution of the sprayed droplets and, consequently, the coverage of the target required by the application.

Widely adopted by farmers, spray tips that produce fine drops generally provide good surface coverage. However, these droplets can evaporate in conditions of low relative humidity or change their trajectory with the action of the wind, resulting in drift of the applied product. Several researchers consider that drops with less than 100 µm in diameter (unit adopted to classify droplet size) are more easily carried by the wind and suffer intensely from the action of weather phenomena.

If very thick droplets are produced, there is no good surface coverage, nor good uniformity of distribution and deposition when spraying over a total area. On the other hand, it is recommended to use thick drops in unfavorable environmental conditions, such as high temperatures, low relative humidity and winds above 6 km/h.

In general, the importance of the size of the droplets produced by the spray tips increases depending on the difficulty in reaching the target and the environmental conditions at the time of applications, and the risks of losses due to evaporation and drift must be considered.

Another important aspect is the application volume. In liquid applications, it is usual to classify the process according to the volume of spray applied per hectare (liters/hectare). Currently, there is a demand from the production sector to reduce the volume of spray sprays. With smaller volumes, there is less transport of water to the field and fewer stops to refill the sprayer, consequently, there is an increase in the operational capacity of the application equipment and a reduction in production costs.

However, when it comes to application volume, it is common for farmers and technicians to have doubts about how to define it. In general terms, the appropriate volume can be defined as the amount of spray necessary to provide maximum droplet coverage with minimum runoff, depending on the equipment or spraying technique used, providing target control.

In the case of the fall armyworm, the greatest difficulty lies in adapting the application volume to reach it with the product, due to the caterpillars migrating and remaining protected in the corn plant cartridge, in which a large part of the insecticide syrup does not reach the target.

Therefore, managing fall armyworm in corn crops has not proven to be an easy task. Given the evolution of resistance to corn crops, Bt and insecticides, which compromise any integrated pest management program, the importance of knowledge in application technology for their management is evident, with economic, environmental and social sustainability of this important crop.

This article was published in issue 142 of Cultivar Máquinas magazine. Click here to read the edition.

Mosaic Biosciences March 2024