Monitoring in integrated pest management in soybeans

Practices such as the use of beating cloth and sex pheromone traps are very useful in the integrated management of pests in soybeans, as they make it possible to quantify the insect population and its fluctuation, determine the level of action and need for control, and adapt insecticide applications. at the most appropriate time, in addition to helping to predict possible population outbreaks.

Among the main causes of reduced crop productivity are pests, which have the capacity to cause direct and indirect damage resulting in reduced productivity, making it necessary to adopt control measures to avoid or reduce the level of damage so as not to compromise productivity. and product quality. Integrated Pest Management (IPM) seeks to combine control practices (chemical, physical, biological and mechanical) with the objective of maintaining the insect population at levels that do not cause significant damage to the crop of interest.

IPM follows basic principles such as monitoring insects to assist in control decision-making, taking into account population density, stage of the pest, damage potential, phenological stage of the crop and biological cycle of the pest. Knowledge of the relationship between the density of a pest and the losses it causes is fundamental for establishing criteria for making decisions about its control within the IPM principles.

The adoption of different monitoring methods depends on the pest and the crop to be sampled. The most used method is the beating cloth due to the ease and simplicity of execution and because its sampling covers a wide spectrum of pests from the aerial part of the soybean crop. However, it presents some limitations such as difficulty in sampling small plants and counting some fast-moving insects. This method allows the determination of the population density of the pest at the exact time of sampling, assisting in decision-making for control, which is carried out when the quantity (population) of pest insects exceeds (reaches) the action level. Another method that has been reintroduced to IPM in soybean cultivation is monitoring using a sex pheromone trap. The resumption of this process is largely due to the discovery of the presence of the pest Helicoverpa armigera in Brazil in 2013. Due to information about the occurrence of this pest in other countries and the difficulty in controlling it, there was apprehension on the part of producers and technicians regarding the management of this pest on Brazilian soil, which led to the resumption of several IPM processes, such as the use of trapping.

The use of pheromones in traps, when compared to light traps or other attractants, has the advantage of capturing specific species of pest insects, facilitating their identification and quantification. The specificity of the species sampled depends on the composition of the sex pheromone used and allows monitoring only adult insects.

The pheromone trap monitoring method allows estimating pest population peaks based on the number of adults captured in the traps. The determination of possible population peaks is dependent on several factors related to the insect's biology and environmental conditions. Therefore, the increase in the capture of adult insects in traps does not necessarily result in an outbreak of larvae (caterpillars) in the crop, as environmental conditions may restrict their occurrence. Therefore, there is no level of action for monitoring Lepidoptera adults in soybeans. However, the increase in the capture of adults raises a warning, as the chances of an outbreak of caterpillars occurring increase. 

In Figure 1 is an example of joint monitoring of pheromone trap and beating cloth, carried out with a false meter (Chrysodeixes includens) in Copacol's area of ​​operation. It is possible to observe that the increase in the number of adults captured in December 2014 increased the number of caterpillars in soybean crops. In this case, insecticides can be used to control small caterpillars, which are easily controlled, especially in the case of the false caterpillar. This species has greater natural tolerance to insecticides when compared to other species. Another obstacle to its control is the habit of feeding on the middle third of soybean plants, which reduces its direct exposure at the time of application and causes it to feed on sub-doses of insecticides, since the pesticides do not arrive in adequate quantities to its control in the middle third of the plants. Estimating adult population peaks facilitates the planning of insecticide applications, minimizing errors, avoiding delays in applications and consequently maximizing pest control.

Among the factors that influence the biology and population dynamics of insect pests, temperature, humidity and food quality stand out. Temperature in general regulates the speed at which metabolic processes occur, directly influencing the biological cycle of the pest.

 Humidity also interferes with the development of insects, varying depending on the species. The low relative humidity of the air favors the loss of moisture to the environment. On the other hand, high relative air humidity provides favorable conditions for the increase of entomopathogenic fungi, influencing the population dynamics of insects.

Food is another extremely important factor in the biology of the pest, determining the population flow of insect pests, directly influencing the development of the insect and also its reproductive capacity as it provides the nutrients necessary for development, and its composition varies depending on the species. , being required in quantity and quality for each phase of the pest cycle. 

The introduction of genetically modified cultivars (GMOs), RR2 generation, which gives soybean crops resistance to the main pest species of the Lepidoptera order, was a major advance in Brazilian agriculture, being a new tool for integrated pest management, ensuring greater stability and safety in crop management. However, monitoring pests in Bt soybean cultivars must follow the same pattern as conventional cultivars, as the action of the Bt protein does not occur on all lepidopteran species, with no control for some species, as in the case of the genus spodoptera, made up of three species, which cause indirect damage to the soybean crop by consuming the leaves and direct damage by consuming pods and grains, presenting a high potential for damage to the crop if not correctly controlled.

The practice of monitoring using the beat cloth method associated with monitoring by sexual pheromone trap, makes it possible to quantify the real population of the area (beat cloth) and the population fluctuation of adults (pheromone), allowing for the adaptation of applications, always taking into account the level of action of the respective target pest for control. It is also possible to predict possible population outbreaks and program applications according to the crop, pest and control method used, so that it coincides with the ideal pest stage for control, the crop stage that facilitates insecticide applications or other control methods used, taking into account the level of pest control through the beating cloth, ensuring efficient control with rational use of insecticides, bringing benefits to the environment, and greater economic return to the producer.

Soy and high yields 

Brazil is the second largest soybean producer in the world and national production has been growing annually, which may be linked to the increase in area, the use of new technological tools (GMOs, precision agriculture, among others) and the management practices adopted . In the 2015/16 agricultural year, Brazil has a total area used for planting soybeans of approximately 33,02 million hectares, with an estimated production of 98,8 million tons, an increase of approximately 2,4 % in relation to the 2014/15 harvest (Conab, 2016).

Obtaining high grain yields is related to the interaction between the genotype, which brings its production potential in its genetic load, the environment that encompasses all the resources available for the plant to grow and develop, thus being able to express its potential, and management practices to maintain productive potential.

Renan Teston, Tiago Madalosso, Fernando Fávero, Copacol

Article published in issue 203 of Cultivar Grandes Culturas.