Effective control measures against stink bugs in soybeans

Stink bugs are important pests that attack the pods of soybean plants and cause serious damage. The limited diversity of registered insecticides with different modes of action, risks of resistance and deficiencies in application technology make these insects the biggest villains in crop productivity today. The inappropriate use of insecticides, without proper sampling, worsens this scenario and increases production costs. Learning to carry out control, using pesticides at the right time, is one of the main challenges for soybean farmers. The key to success lies in pest management.

Among the most important pests of soybeans are stink bugs, insects that attack the pods of this plant. The limited diversity of registered insecticides with different modes of action, the proven resistance of pest populations to existing insecticides, associated with deficiencies in the technology for applying these products, make this pest complex the biggest villain in crop productivity today. Furthermore, the erroneous use of insecticides, with “preventive” application without proper sampling, worsens this scenario and increases production costs, without any benefit for the producer. Learning to control the pest with the use of insecticides at the right time is one of the main challenges for soybean farmers and the key to success  lies in managing the pest.

There is a great diversity of stink bug species that can attack soybeans, however, the most abundant and important on the national scene is, without a doubt, the brown stink bug, euschistus heros. These insects directly damage the grain tissues, making them flat and wrinkled, affecting the production and quality of the grains produced. The injuries caused by insects during their feeding facilitate the contamination of grains by pathogens and can also cause physiological disorders, such as delayed maturation, leaf retention and abnormal development of follicles and pods. However, it is important to highlight that the greatest damage to crops due to the attack of this pest occurs mainly due to the abandonment of the Integrated Soy Pest Management (MIP-Soja) and the use of insecticides in a “calendarized” or “piggyback” manner. ” with herbicide and fungicide sprays. To successfully control bed bugs, it is necessary to correctly use the main management tools available, among which insecticides are worth highlighting.

CORRECT USE OF BEDBUG CONTROL

chemical control

Chemical insecticide is currently the most important tool in bed bug management and, when used well, brings benefits to the producer. However, unnecessary spraying, carried out without adopting agronomic criteria, can cause great harm such as increased production costs, selection of resistant insect populations, in addition to even greater pest outbreaks than in the absence of application. The growing increase in the production cost of soybean crops is a reality that has been worrying rural producers. Part of these expenses is due to the incorrect and unnecessary use of agrochemicals. When comparing spending on pesticides between the 2002/2003 and 2012/2013 harvests (Figure 1), it is possible to notice this significant increase. Part of these expenses can be reduced by avoiding the unnecessary use of insecticides.

Soybean farmers, fearing losing control of stink bugs, often choose to apply insecticides at low populations or when the pest is not yet causing damage, such as during the growing season, for example. However, by doing this, it only selects insects that are more resistant to the insecticides used, which worsens the attacks that will occur in the reproductive period, when the pest is really harmful.  

It is important that the producer does not use insecticide in any pest infestation or preventively. The application of insecticides needs to be economical and therefore only justifiable when the bed bug population is at or above action levels (represented by the economically correct time for a control measure to be initiated) and thus prevents the insect population from growing. too much and cause economic losses.

Unfortunately, the incessant search for increased productivity, associated with the good prices paid for soybeans and the low cost of many insecticides, has led many professionals to recommend early applications to control bedbugs. This caused many producers to abandon pest sampling and the use of action levels, starting to apply insecticides to soybeans together with post-emergence herbicides or fungicides in the reproductive phase. This has even been done in an attempt to take advantage of the agricultural operation that is being carried out. With this erroneous application of insecticides carried out together (“piggybacking”) with herbicides and fungicides and no longer at the level of action, the control of stink bugs in soybeans has shown disastrous results. Currently, up to three or four insecticide applications are used to control this pest, totaling six or more insecticide applications in a single soybean harvest, which is certainly excessive and can be rationalized with the use of IPM-Soja .

The rational use of insecticides is already a reality in Paraná. In this state, MIP-Soja has been carried out in several municipalities in a state program called “Plante your Future”. In these management areas (reference units: URs) technicians from the Technical Assistance and Rural Extension Company (Emater) provide assistance and introduce MIP-Soja to producers. With this, it has already been possible to reduce the use of insecticide applications by approximately 50%, in addition to increasing the interval between the first application from 35 days to 63 days, thus allowing greater preservation of natural enemies and providing less impact resulting from the application of chemical insecticides ( Figure 2).

These results were obtained because the producer applies insecticides only when really necessary (at action levels), and thus, unnecessary applications are eliminated. Recent research results, with some of the new soybean cultivars (early cycle and indeterminate growth), show that the action levels are reliable and indicate the best time for the soybean farmer to start applying insecticides wisely, preserving crop productivity, as well as the environment. In experiments conducted in the municipality of Arapongas, Paraná, during different harvests, the productivity and quality of seeds were compared after the use of insecticides in different intensities of bed bug infestation: NA of bed bug (average of 2 bed bugs/m); ¼ of the bed bug NA (average of 0,25-0,5 bed bug/m); preventive (application associated with herbicides and fungicides) and control (without applications) (Table 1). 

The results obtained demonstrated that even with a smaller population of bedbugs in the treatment that was considered ¼ of the action level in relation to the other treatments evaluated (Figure 4), there was no significant gain in productivity (Table 1). On the other hand, this treatment certainly had a higher economic and environmental cost, since six applications of insecticides were necessary, while in the treatment that followed the level of action recommended by the research (2 bedbugs/m), there was a need for only two applications of insecticides. insecticides (Figure 3). It is important to highlight that the observed productivity differed only between the treatments with applications, regardless of the criterion used, and the control without insecticide application (Table 1). When evaluating stink bug damage (scale 6-8 in the tetrazolium test), only the control showed a high level of damage, with 13,7% of grains with non-viable seeds. Treatments 1 (2 stink bugs/m), 2 (0,25-0,5 stink bug/m) and 3 (preventive) were statistically equal and resulted in percentages of non-viable seeds lower than 6% (Table 1). This intensity of damage is still accepted for seed production, whose standards are more demanding in relation to grain production, proving once again the safety of the recommended action levels.

Biological control

Among the natural enemies of bed bugs, the “wasp” telenomus podisi 4, an egg parasitoid, deserves attention for its parasitism capacity. Several studies show that T. podisi It has a longevity of around 32 days to 45 days, depending on its host, and its females have the ability to parasitize eggs for an average of 10 days. This species is found in different agroecosystems and one of its main characteristics is its preference for eggs. E. heroes, in addition to a great ability to search for these eggs, which can be hidden in the plant and in places that are difficult to cover by the traditional application of insecticides. Thus, the parasitoid finds the bedbug eggs, oviposits inside these eggs, and after approximately 14 days, adults emerge that will continue the control, providing a lasting effect, compared to conventional chemical control.

Another advantage in using egg parasitoids in IPM-Soja is the fact that control is exercised over the egg, before damage occurs. This allows that, if there is any control failure, another management measure can be adopted without harm to the crop's production. The use of this parasitoid still depends on research that establishes all recommendations for its use (technological package), with investigations being underway at different research institutions such as, for example, Embrapa Soja, Universidade Estadual de Londrina (UEL), among others. Furthermore, the use of the parasitoid must be duly registered with the competent bodies so that they can be recommended in the field. Given this, it is believed that soon T. podisi can be used as a control alternative for euschistus heros, helping to maintain the stink bug population at levels that do not cause damage to the crop. 

FINAL CONSIDERATIONS

Currently, stink bug infestations have increased significantly in soybean crops throughout Brazil, mainly of the species E. heroes. This has occurred due to a set of factors such as the selection of bed bug populations resistant to the main insecticides used; lack of availability on the market of insecticides with different mechanisms of action; deficiencies in application technology; and ecological imbalance caused by the abusive and disordered use of broad-spectrum insecticides, right at the beginning of the development of the crop and abandonment of IPM-Soja.

Therefore, for the correct management of this insect, it is necessary to control bedbugs with insecticides only from the R3 stage (beginning of the first pods) when the population is equal to or greater than the action levels (through well-executed monitoring with the aid of cloth -de-beat); adopt action levels (2 stink bugs ≥ 0,3 cm/meter for soybeans intended for grain or 1 stink bug ≥ 0,3 cm/meter for soybeans intended for seed) including for the most modern cultivars (early soybeans and indeterminate growth) ; use table salt (0,5% of the volume of syrup – v/v) in the insecticide syrup when soy presents challenges for the application technology (salt helps the bedbug to become contaminated with the insecticide, as it causes the insect to remain longer on the leaves exposed to the application). Care must be taken to wash the equipment thoroughly after application, because salt residue in contact with the metal can cause it to suffer a corrosion process.

Always rotate the insecticides used (≠ modes of action); reserve the use of mixtures (neonicotinoids + pyrethroids), acephate or another product recommended for bedbug control, only for the soybean reproductive period. This reduces the selection pressure for bed bugs resistant to these insecticides and preserves their action to control this pest for a longer time.

These pest management precautions will help the soybean farmer to manage his crops well, using less insecticide and achieving good productivity.

Adeney de Freitas Bueno, Daniel Ricardo Sosa-Gómez, Embrapa Soja; Débora Mello da Silva, Agronomic Institute of Paraná (IAPAR)

Article published in issue 207 of Cultivar Grandes Culturas.