| Brown Root Bug

Brown stink bug management

Insect sucks the roots of plants, causes a marked delay in development and, consequently, harms production

13.05.2020 | 20:59 (UTC -3)

Brown stink bug population outbreaks (Chestnut Scaptocoris) has become common in soybean, corn and cotton crops in the Cerrado. With an underground habit, this insect sucks the roots of plants, causing a marked delay in development and, consequently, damaging production. Preventive measures such as using entomopathogenic fungi and nematodes, ammonium and calcium sulfate, applying insecticides in the planting furrow, improving the nutritional conditions of the cultivated area and including cover crops with a suppressive effect during crop rotation are among the recommended alternatives for managing the pest and minimize losses.

In rotation or succession schemes, the selection of crops that are not common hosts for pests and diseases is one of the fundamental strategies for integrated pest management (FERREIRA et al., 2012). In the areas of the Cerrado where cotton has been cultivated, a large complex of pests affects and causes damage to the plants, requiring constant attention and possible interventions to avoid economic damage.

Occurrences of population outbreaks of brown stink bugs (Scaptocoris castânea) have become frequent in plantations in the Cerrado, especially in the cultivation of soybeans, corn and cotton. With an underground habit, the insect sucks the roots of plants, causing a marked delay in development and, consequently, damaging production. Studies carried out by researchers from several Brazilian research institutions show that chemical control adopted in isolation is insufficient, as it does not treat the cause of the problem. Chemical control is not more than 50% efficient and the presence of corn in the rotation scheme is a factor that favors the proliferation of brown stink bugs. When damage is found in the crop, there is not much that can be done, as the attacked plant has difficulty recovering and production is compromised.

Crops with failures caused by the incidence of brown stink bug attacks.

In recent studies, Nascimento et al. (2014) verified the influence of the use of sulfur compounds on the brown stink bug population in cotton crops. The authors did not find evidence of the influence of agricultural gypsum or sulfur fertilizers applied to the soil inducing the population reduction of Scaptocoris sp. However, the study concluded that the use of such sulfur sources (calcium sulfate and ammonium sulfate) promotes the tolerance of cotton plants to insect attack.

The brown stink bug has also been associated with invasive plants, listed in descending order of preference: caruru, fire extinguisher, trapoeraba, picão-preto, among others (SILOTO & RAGA, 1998). Likewise, some cultivated plants such as millet and maize appear to be preferential to individuals of these soil pest species. On the other hand, empirical observations from producers point to sunn hemp as a possible suppressive species (José Roberto Padezi, personal communication).

Strategies such as improving the nutritional conditions of the cultivated area and including cover crops in the rotation scheme that have a suppressive effect on the pest population are highlighted as ways to reduce the insect population and ensure the profitability of cultivation. Other measures that have shown good results in dealing with the pest include the use of sulfur compounds and cover crop options.

A trial carried out by Embrapa Algodão in partnership with Fundação Goiás aimed to evaluate the effect of cover crops on the incidence of brown stink bug in cotton grown in a direct planting system (SPD). The treatments consisted of the inclusion of 14 different cover species in a rotation scheme after the cultivation of soybean, corn and cotton crops. During cotton cultivation, at the end of the rainy season, when the plants were 60 days after emergence, the following parameters were measured: visual appearance (by rating scale), number of attacked plants, plant height and area used by plants. At the end of the cycle, seed cotton productivity was quantified.

Unattacked cotton plants tend to take up space in the area not occupied by adjacent plants whose growth and development have been compromised (CAWLEY et al., 1999). This spatial compensation effect was verified in the present study, since no difference was observed in terms of the area used between treatments (Table 1). Likewise, no difference between treatments was observed regarding the number of bolls per plant, plant height, fiber yield and e.g.stood.

The visual assessment carried out at 60 DAE showed a worse appearance in the plots treated with cotton cultivated after covering with millet, with a score significantly lower than those recorded for all other treatments, except P.maximum, B. brizantha, millet + B. ruziziensis e guandu + B. ruziziensis. Millet also stood out for presenting the highest number of plants attacked by the brown stink bug, with a value higher than those recorded in treatments with cotton after fallow, pigeon pea and sesame + B. ruziziensis (alternating rows).

The productivity of seed cotton in the treatment with cotton after millet was the lowest among all treatments, with a value significantly lower than those observed with cotton after pigeon pea and sunflower, both species intercropped with B. ruziziensis.

When species are grouped into families, considering legumes, grasses and their associations, it can be seen that the average productivity of cotton cultivated after legumes was above the value obtained for cotton following associations, which in turn was higher than the average cotton productivity after grasses (Figure 1). Therefore, despite there being no statistical differences, there was a tendency towards greater productivity in cotton cultivated after species that suppressed the brown stink bug population.

Figure 1 - Productivity of cotton grown after cover crops from the legume families, grasses and their associations. Santa Helena de Goiás, 2013.

Management and control measures

If chemical control of the brown stink bug has not always proven to be effective, the insect is very little exposed to the insecticide, its polyphagy and migration habit every year contribute to making it difficult to control the pest population, preventive measures must be adopted.

The use of entomopathogens such as fungi and nematodes has proven to be an option to reduce the pest population in problem areas. Entomopathogenic nematodes of the genera Steinernema e Heterorhabidits are already marketed for the control of soil pests. Other entomopathogenic organisms that have shown lethal effects on brown bed bugs are fungi, Metarhikum anisopliae e beauveria bassiana. In work carried out by Ávila & Xavier (2007), these fungi showed control over nymphs and adults, with mortality rates exceeding 50%.

The insect sucks the roots of plants, causing a marked delay in development and, consequently, damaging production.

Improving soil and climate conditions, providing better nutritional conditions for cultivated plants may be another option. Work carried out by Nascimento et al. (2014) found that the application of ammonium sulfate at concentrations between 150 kg/ha and 300 kg/ha, combined with 1.500 kg/ha of calcium sulfate, promoted a significant reduction in brown stink bug infestation and, consequently, increased productivity. of culture.

Chemical control with the application of insecticides in the planting furrow may be a curative measure to be considered. Insecticides such as chlorpyrifos, imidacropid, fipronil and thiamethoxam provide a greater reduction in the number of brown stink bugs than when they are applied conventionally.

In general, other measures that can be proposed for successful management of brown root bug.