How to carry out integrated and rational bed bug management

With the potential to irreversibly affect quantity and quality of soybean production, bed bug attacks can result in losses even after harvest, under certain storage conditions. The management integrated and rational approach to these insects, with regionalized actions, which include other tools in addition to chemical control, is indispensable to face this great problem in crops.

When there is a group of insects in a soybean crop that can affect irreversible way in the quantity and quality of production, the risk of its presence becomes large and if the problem is not treated in time, this damage tend to cause losses even post-harvest, going beyond discounts at the time of marketing. This is the case with damage caused by bedbugs, euschistus heros e Piezodorus guildinii, species considered, within the complex of phytophagous soybean bugs, with the highest incidence. They represent more than 90% of total population of pentatomids that occur in the culture, with a predominance of one species or another, according to the region, year, or cultivar used.

Although colonization by bedbugs begins in the middle or end of the vegetative period of the crop, its presence is worrying, especially in reproductive phase of soybeans, as from the appearance of the pods, the populations of these phytophages increase considerable size, with its individuals feeding mainly on developing grains, causing wilting and poor formation of seeds and pods (Figure 1). Furthermore, in some cases, the attacked soybean plants do not They ripen normally, remaining green at harvest time.

O The problem is that by damaging the grains, these stink bugs promote large damage, even with a single sting. They just need to be able to break the integument and reaches the cotyledon and then this grain begins a process that irreversibly alters the humidity and balance internal, in addition to facilitating the penetration of microorganisms and water. Consequently the fermentation process can start already in the fields, mainly in rainy periods, and continue post-harvest depending on the conditions of storage.

Please note that throughout the culture management process there is a high investment for achieve good productivity. Although, Often the quality of the grains is poor and in this case the problems begin to be detected at the time of classification of these grains, when arrive at the storage units, that is, before marketing and packaging of batches in warehouses. Through official standards approved by the Ministry of Agriculture, Livestock and Supply (Mapa) and with based on the normative instruction MAPA 11/2007, it is determined the Group, Class and Type of soybeans. Therefore, a sample is analyzed and, specifically, the grains that present a “white spot”, as seen in Figure 2, caused by the stink bug feeding, are identified as a “mild” defect and called grains “chopped”. In this type of defect the discount is not total, as occurs with other defects observed in the same classification. This is because from the obtaining the percentages of chopped grains, these are divided by four and then added to the total number of damaged grains. This results in a discount, according to the limits exceeded, applying discounts on batches of grain marketed. However, the problem may intensify over time, when depending on storage conditions, a fermentation process of those “chopped” grains, which come to be known as “fermented” grains. Therefore, based on the regulations, the discount in this case will be total (it will no longer be divided by four, as occurred at the time of receipt of this grain after harvest), and the losses will come from sales future ones and will be the responsibility of the storage companies and/or the producer who stores on the farm itself.

In addition of the damages already mentioned, this fermented grain also causes changes in the raw material that goes to industry, promoting changes in color and an increase in acidity of the oil, which increases costs in the bleaching process and neutralization of this acidity and as a consequence there is a lower yield in extraction of this oil. That damage often cannot be avoided, because as shown in Figure 3, Even with populations under control, it was not possible to prevent a small part of the grains was damaged, however, it remains to be seen whether this percentage of chopped grains, even if it is lower than the limit accepted by Mapa standards, come causing a slow fermentation process within the storage units, compromising the entire batch.

It is extremely important to establish or resume integrated management of pests in soybean crops, with the aim of minimizing all this harmful process caused by bedbugs. Control tactics for this pentatomid complex have been known for years, but unfortunately, most has a habit of applying pure and simple insecticides and what is worse, of scheduled way, that is, based on the development of the culture, or taking “free ride” with fungicides, therefore without prior monitoring.

As is public knowledge, the use of insecticides in mixtures of tank with herbicides, or even fungicides, despite not being regulated, is a common practice for soybean farmers, and this procedure, which is justified by the exploitation of operations, has increased problems in relation to control, simply because the target pest is not present, or on the contrary, it is already present, but in high populations and, probably, the effectiveness of the insecticide may be compromised, not to mention the reductions in the quantity and quality of grains that will be harvested.

When talking about integrated pest management, many have in mind the idea of ​​organic agriculture, without agrochemicals, but that is not the scope. For the Otherwise, the chemicals are present, they are part of the process, but they are not nor can they be the only tool to be adopted. It is necessary to include within the production system, in addition to agrochemicals, biological control tactics, such as the release of natural enemies of key pests and their maintenance through the use of more selective insecticides and/or also adopting microbial control in culture. These are fundamental tactics for establishing integrated management of pests, as they allow natural enemies to also act on the control of phytophagous bugs.

Furthermore, many techniques related to cultural control are applicable to large and small intensive agriculture, having as examples, the combination of crop rotation, the destruction of crop residues to interrupt the life cycles of phytophages, the timing or disposal careful planting to avoid synchronization with pests, the destruction of host plants, or the cultivation of trap plants for attraction and control of bedbugs. Or, even, those that can preserve the population from enemies natural resources close to crops.

Is important consider that with the harvest, the population normally decreases and bedbugs begin dispersal to host plants and then take shelter in straw areas, remaining until the next soybean harvest, especially in the case of of the brown stink bug. Therefore, the identification of locations where these insects take refuge to, eventually controlling them would be a very effective way if carried out at the end or beginning of the harvest, thus avoiding the entry or exit of these bed bugs to refuge areas.

Therefore, there are several options in addition to chemical control, which aims to objective, to reduce phytophagous stink bug populations in soybeans. However it is It is important to know that the basis for all pest management is the correct identification and quantification of insects present in the crop, and this can only be achieved with successive and frequent monitoring, which is not usual practice of soybean farmers.

In monitoring, the producer must hire trained personnel to monitor the rapid recognition of pests and natural enemies present in the crop of soybeans, and follow with the simplest of methods, that of beating the cloth, using, for this purpose, fabric or canvas of a different color. clear, 1 m wide and 1,40 m long length, fixed on two sticks. The cloth must be laid out carefully between the rows of soybeans, unfolding one part and adjusting it at the base of the plants that will be harvested, and the other part extended over the soybean plants of the adjacent row. Then, the plants must be shaken vigorously on the cloth, promoting the fall of insects that must be identified and quantified, first the adults and then the young forms (Figure 4).

Under no circumstances should the producer make decisions based on assessments visuals, as they are not representative and can lead to mistakes. Works carried out in Goiás demonstrated that in the batting stage, regardless of the hourly, the extraction of bedbugs was approximately ten times greater when compared to a visual assessment of the plants (Figure 5).

It's from knowledge that adults are viewed more frequently by the producer. However, monitoring shows that nymphs remain longer in the middle parts of the soybean, apparently hidden between the pods, causing damage and losses similar to those caused by adults and despite the stink bug can feed on various parts of the plant, it is the pod with its grains, the most preferred food. Therefore, spraying with insecticides must be targeted to reach this population, mainly in the middle and lower thirds of soybeans.

Furthermore, studies show that first instar nymphs do not feed. On the other hand the third, fourth and fifth instar nymphs are able to reach with their sharpen the forming grains, irreversibly damaging them. It's needed remember that, at this stage, the young form does nothing other than nourishment and tends to direct all energies towards this purpose. Therefore, they represent a threat in the final stretch of the cultivation, when the yield and quality of the seed are defined. Already adults feed like young forms, but fly and spend part of the time also with mating and oviposition, aiming to perpetuate the species.

A intensity of damage will depend, fundamentally, on the species of bedbug and their stage of development, the phenological stage of the plants and the time in that these insects will continue to feed, beyond, of course, the level existing population in the crop.

Sampling must be carried out weekly, throughout the cycle of soybeans and in a number of ten per 100 hectares and intensified, depending on the development phase of the crop and adjacent plantations. The increase in this procedure during the crop's reproductive period is essential and the average all sampled points should be indicative for the adoption of control, or not. For this, there are the control levels recommended by research bodies, (two stink bugs/m for soybean grain and one stink bug/m for soybean seed). However, these levels have been questioned by researchers and technicians in the area, who consider them, within the current panorama of soy, excessively high, inflexible and outdated. There is a tendency adopting 0,5 bedbugs/meter, regardless of the production destination, mainly in late soybeans.

Regarding control before the appearance of pods, most Studies agree that bed bugs at this stage do not cause reductions in yield and grain quality. Therefore, control measures would not be justified. However, they are frequently observed at the end of the vegetative period and beginning of the flowering period, areas with high densities of adult bed bugs, from refuges or more advanced cultivation. In this case the maintenance of these insects can often trigger population levels difficult to control, as they will leave descendants that in a few days will be in the forming pods and consequently damaging grains. Therefore, the decision to control may be an alternative to consider, with the differential when there are, within the production system, soybean crops in different development phases.

It is necessary to highlight that the soybean plant can compensate for the losses arising from insects that attack the grains. However, only when the damage occur at the beginning of pod formation, when they are able to counterbalance damage by increasing grain weight or retaining more pods. However, this will not be possible if there is a constant presence of bedbugs throughout the development of culture, especially between R5 and R6, as in these phases, the pod damage can result in significant production loss, not to mention quality that can be affected, and in the latter case, is known only in the moment of marketing.

Monitor the crops, even in the final stages of soybean maturation (R7 and R8), is extremely important, as the high populations coming from other crops, or remaining populations, can also harm the quality of the grains, especially if the cultivation is for seed, in addition, possibly, these populations will later migrate to other crops or refuges, perpetuating the problem of these suckers in the area.

Until the research impasses are resolved, it is best to tell with common sense, as control effectiveness will depend on several factors, such as location of the crop, crop and insect phases, soybean plantations in surroundings, cultivars used, equipment available for application, application time, choice of insecticide, among others. O It is important to clarify that 33 million hectares of area planted with soybeans (2015/16 harvest) cannot be managed under the same recommendations, as agriculture is a dynamic process and tends to undergo large or small variations over time and between different growing regions.

Ultimately, there is a need for regionalization of management Integrated Pest Management (IPM) in Brazilian production systems, adopting sustainable tools from a socio-environmental point of view with the aim of increasingly productive harvests per unit area are achieved, but with grains of good quality, since the soybean market is mainly based on oil and in protein content.

Morphology and Biology

Euschistus heros (Brown stink bug)

The brown stink bug lives predominantly in tropical regions and subtropical, corresponding to the main grain producing areas in Brazil As the common name suggests, its color is brown. The adult has two pointed lateral extensions on the pronotum (the spines). The nymphs have Varied coloration, from greenish to dark brown.

The eggs, beige in color, in small numbers (5 to 8 per clutch), are deposited in the leaves and pods of the plant and when they are about to hatch, have a pinkish stain. Newly hatched nymphs exhibit gregarious and do not cause damage to the crop. It is from the third stage that begin to disperse, mainly among the pods in the middle third of the plants, in order to suck the soybeans (Figures 6 and 7).

Piezodorus guildinii (Small green stink bug)

Bedbug approximately 1 cm long. Has color light green with a brown, red or yellowish transverse stripe on the prothorax. The postures, dark in color, are presented in double rows containing from 10 eggs to 30 eggs, preferably in pods, but they can also be found in leaves, stem and branches. The nymphs soon after hatching have reddish abdomen and dark head and thorax. During this period, like the brown stink bug nymphs remain grouped close to the eggs. When are more developed, acquire a green color with dark, reddish spots in the thorax and abdomen and disperse throughout the soybean plants, attacking, mainly, grains in formation (Figures 8 and 9).

Article published in issue 215 of Cultivar Grandes Culturas, April 2017.