Integrated management of caterpillars and stink bugs in crops

Economic benefits through cost reduction and environmental benefits through greater balance in the agroecosystem are among the advantages of integrated pest management, such as the false caterpillar and the brown stink bug, in soybean crops. 

Soybeans can be attacked by pests from plant emergence to physiological maturity. These pests are classified as of primary, regional or secondary importance, depending on their frequency and scope of occurrence and the potential damage they cause to the crop.

In the early 1970s, before the implementation of integrated pest management (IPM) work in soybeans, six to seven insecticide applications were carried out during the crop cycle. From 1975 onwards, IPM-soybean work began in Brazil through a partnership involving different research and rural extension institutions. After determining the damage levels for the main defoliating and sucking pests in the crop, it was recommended to use insecticides only when necessary, that is, when pest populations were equal to or above the control level. After a few years, that alarming situation regarding the use of insecticides in soybean crops was reversed to an average of just two applications per harvest. In the 1980s, biological control of the soybean caterpillar was developed through the use of baculovirus anticarsia which further boosted the IPM-Soja in Brazil, while in the 1990s, the biological control of phytophagous stink bugs through the use of egg parasitoids was also included in the soybean IPM.

However, in the last decade, there has been a setback in soybean pest management programs or even, in many situations, the abandonment of this strategy, returning once again to an abusive increase in the use of insecticides in crops, with undesirable consequences from the point of view. from an economic, ecological and environmental point of view. In this new scenario, insecticides are no longer used based on the population of pests sampled on crops, disregarding the action levels recommended by research, with spraying being carried out based on subjective criteria, with applications often being of insecticides scheduled based on calendars. With the advent of transgenic RR soybeans resistant to the herbicide glyphosate and the arrival of Asian rust in Brazil in 2001, applications of herbicides and fungicides to soybean crops increased sharply. This increased use of fungicides and herbicides in crops, in addition to applications of broad-spectrum insecticides, has contributed to the biological imbalance in the agroecosystem, as a result of the destruction of the natural enemies of insect pests. This biological imbalance has caused the frequent appearance of resurgences of the main pests, as well as the eruption of secondary pests, such as the false caterpillar, Chrysodeixis includens. In addition to this, in recent years the development of resistance of phytophagous stink bugs to chemical insecticides applied to soybeans has been noted, increasing cases of unsuccessful pest control in the crop.

Faced with this chaotic scenario, there is an urgent need to develop, update and/or adapt new concepts and strategies for pest control in soybeans, to restore integrated management in the crop so that its benefits can be enjoyed. Work coordinated by Embrapa Soja, especially in the State of Paraná, has shown that IPM constitutes an important tool for rationalizing the use of insecticides in soybean cultivation, without risking productivity losses.

Research was also conducted in Mato Grosso do Sul to establish the monitoring and integrated management of insect pests and their natural enemies in soybeans, as well as carrying out an economic analysis of the costs and benefits of this pest control strategy in the crop.

Research methodology

Integrated pest management (MIP-Soja) was carried out during the 2015/2016 harvest in a producer area, in the municipality of Dourados/Mato Grosso do Sul. Soybean sowing was carried out on November 07, 2015 with the cultivar Syn 1059 (Vtop), with the emergence confirmed on November 14, 2016. The soybean seeds in the area where the IPM was conducted were treated with the insecticide chlorantraniliprole at a dose of 1 mL/kg of seeds of the commercial product, while in the area led by the producer, the seeds were treated with fipronil at a dose of 2,0 mL/kg of seeds of the commercial product, considered the comparative standard for IPM. The other agronomic practices for implementing and managing crops were carried out in accordance with the Technical Recommendations of the Soybean Research Commission for the Central Region of Brazil.

Monitoring of defoliating caterpillars

With the appearance of the first soybean leaves, sampling of caterpillars that attack the aerial part of the crop began, and this monitoring was carried out weekly until the grain filling phase. The caterpillars were monitored using the cloth at eight different points, both in the MIP area and in the producer's area.

Delta-type traps were also installed, which contained the sexual pheromones of Spodoptera frugiperda, helicoverpa sp. Heliothis virescens e Chrysodeixis includens. The septa of the traps containing the sex pheromone were replaced monthly and the adhesive floors weekly, when the adults collected in the traps were identified and quantified.

Monitoring of pests that attack pods and grains

Close to the beginning of the soybean flowering period, stink bug monitoring began in the two soybean areas (MIP and the producer), using the cloth. When the population density of caterpillars or stink bugs in the MIP area reached the control level for these pests or was positioned close to it, insecticide applications were carried out on the soybean crop. Pest control in the producer's area was carried out according to its guidelines.

Economic analysis of pest management in the project

In the economic analysis of the two management systems (IPM area and the producer's area), the costs of insecticides, machine operations, implements and labor per hectare were considered. In addition, an extrapolated analysis was made of the economic benefits of pest management in the IPM area, in comparison to the total area of ​​soybean cultivated by the producer, as well as considering the soybean production scenario at the state and national level.

Results achieved

In sampling adult lepidopterans, using traps baited with sex pheromones, four species of moths were found in which their pheromones were tested. The species SPodoptera cosmioides e Chrysodeixis includens were those with the highest incidence in pheromone traps, with the peak of the first observed in December and the second in January (Figure 1). Although adults S. frugiperda Although they are abundant in sex pheromone traps, this species was not economically important in soybean cultivation.

Among soybean defoliating caterpillars, the most abundant species was C. includens. Based on data from sampling of caterpillars with the cloth, decisions were made whether or not to apply insecticides to control these pests in the IPM area. The peak abundance of caterpillars in soybean occurred on January 7, 2016, both in the IPM and rural producer areas (Figures 2 and 3), a period in which soybeans were in the initial stage of pod development ( R3).

To control caterpillars in the MIP area, only one application of the insecticide chlorantraniliprole was carried out on December 30, 2015, using a dose of 60 mL/ha of the commercial product (Figure 2 and Table 1). This first spraying of soybeans was carried out only 66 days after the emergence of the plants, an ideal condition for the implementation of IPM, since this late entry of insecticides into the crop promotes the development of natural enemies in the agroecosystem, creating a condition of biological balance. In the soybean area managed by the producer himself, four insecticide applications were carried out to control caterpillars (Figure 3), with the first spraying carried out with methomyl on December 17, 2015, with a dose of 1 liter/ha of the commercial product. , the second with the insecticides lufenuron + profenofos at a dose of 400 mL/ha of the commercial product, the third with the insecticide spinetoram at a dose of 100 mL/ha of the commercial product and fourth with the mixture methomyl + spinetoram at doses of 1,0 liter/ha and 100 mL/ha, respectively, of commercial products (Table 1).

Regarding the occurrence of phytophagous stink bugs in soybeans, a greater predominance of adults was observed in relation to nymphs, both in the IPM area and in the area managed by the producer. In the IPM area, three insecticide applications were necessary to control bedbugs, the first being carried out with the insecticides thiamethoxam + lambda-cyhalothrin + salt, at a commercial dose of 300 mL/ha + 0,5% NaCl, the second with the insecticides imidacloprid + bifenthrin + salt, at a commercial dose of 400 mL/ha + 0,5% NaCl and the third with the insecticides thiamethoxam + lambda-cyhalothrin + salt, at a commercial dose of 300 mL/ha + 0,5% of NaCl (Table 1). In the area managed by the producer, three applications were carried out (Figure 5) using only the insecticides thiamethoxam + lambda-cyhalothrin at a dose of 300 mL/ha of the commercial product (Table 1)

By analyzing the cost of insecticide applications on soybeans, it was found that in the area where the IPM was carried out there was a saving of R$ 125,58 (one hundred and twenty-five reais and fifty-eight cents) per hectare (Table 2) . The producer who owns the area where the IPM was conducted cultivates an area of ​​360 hectares of soybeans. If I had followed the MIP guidelines, the farm would have saved R$45.208,80 (forty-five thousand, two hundred and eight reais and eighty cents). Extrapolating this cost reduction value to the state of Mato Grosso do Sul, which had an area cultivated with soybeans of 2.430.000 hectares in the 2015/2016 harvest, the state economic benefit would be R$ 305.159.400,00 (three hundred and five million, one hundred and fifty-nine thousand and four hundred reais), while for the Brazilian scenario, which had a cultivated area of ​​33.228.400 hectares in this same harvest, the economic benefit would be around R$4 billion (Table two).

Final Words

The main species of soybean defoliating caterpillar in both the Integrated Pest Management (IPM) and producer areas was the soybean caterpillar, C. includens, while the predominant species of bed bug was the brown, E. heroes. Based on the pest management results obtained in the IPM area and the producer, it can be concluded that pest control in soybean crops, following the IPM principles and philosophy, constitutes a practice that brings economic benefits to producers rural. This result is achieved because this control strategy promotes a reduction in the number of insecticide applications per harvest which, consequently, reduces the phytosanitary cost of soybean crops, thus guaranteeing a greater profit margin for the rural producer.

In addition, the use of IPM in soybean cultivation promotes natural biological control in the agroecosystem and reduces environmental contamination, since fewer products are dumped annually into the environment, which represents an improvement in the population's quality of life.

With the addition of other pest control tactics in soybean cultivation, associated and in harmony with IPM, such as transgenic Bt plants and applied biological control of caterpillars and stink bugs using parasitoids, it is expected that the required number of insecticide applications in the crop can be further reduced, thus leading to the establishment of a more balanced biological environment in the agroecosystem and cleaner from an environmental point of view.

It is expected that the results obtained in this research can stimulate technical assistance and rural producers to use Integrated Pest Management more intensively in their soybean crops and, with this, obtain the economic, environmental and social benefits that this strategy of pest control provides, as was found in this study.

Crébio José Ávila, Embrapa Agropecuária Oeste; Viviane Santos, Federal Institute - Ponta Porã, MS

Article published in issue 211 of Cultivar Grandes Culturas.