The Impact of Pesticides - Academy Publish

It is important to emphasize that the soybean plant has the characteristic ofproducing leaf area in excess. This characteristic, which is also present in other plantspecies, allows that even with some defoliation, these plants still achieve maximuminterception of solar radiation for photosynthesis (BROUGHAM, 1956, 1958; &DONALD DAVIDSON, 1958, and Watson, 1958, MURATA, 1961, STERN &DONALD, 1962). This happens because a small loss of leaf area can becompensated by the greater light penetration until the lower leaves, which were onceshaded, leading to an increased total production of photosynthesized products by theplant and making them producing a grain yield similar to the plants withoutdefoliation or even inducing a slightly higher yield than the non-defoliated ones(TURNIPSEED, 1972).In addition to the defoliator insects of the soybean crop, there are the stink bugs,which usually are a complex of different species that attack the pods sucking thegrain contents. These pests are gaining importance in Brazil and some othercountries. Questions about the viability of the ET recommended to initiate thecontrol for this pest are also raised, particularly with respect to the early soybeancultivars with indeterminate growth habits.Economic Thresholds for Stink BugsA study in this subject was carried out in the field, in the municipality of Arapongas,State of Paraná, South Brazil, during the 2010/2011 crop season. This study aimedat comparing the efficiency of the management used for different intensities of stinkbugs infestations [ET (2 stinkbugs ≥ 0.5 cm / meter); ¼ ET (0.5 stinkbugs ≥ 0.5 cm /meter)] and the application of insecticides mixed with herbicides and fungicides (anincreasingly common practice adopted by some Brazilian soybean growers in anattempt to reduce control costs) in the management of pests of the soybean crop.The treatments evaluated were applications of insecticides (or mixtures of them) atdifferent crop developmental stages (Table 1). The experimental area was sownwith the soybean cultivar ‘BMX Potência RR’ (maturity group 6.7 andindeterminate growth habit). The applications of herbicides and fungicides wereequally carried out for all treatments, including the control plot. The pest populationwas weekly assessed with the aid of a sample-cloth on four sites per plot.The results of this study indicated that, in general, even with a smaller population ofstink bugs in the treatment with ¼ of the ET (0.50 stink bugs ≥ 0.5 cm/meter -treatment 2) as compared to the other tested treatments (Figure 7) this treatment didnot have any significant gain in productivity (Table 2). In contrast, this treatmenthad higher number of insecticide applications and, consequently, higherenvironmental costs, since six applications of insecticides were performed, while thetreatment 1, which followed the ET recommended by research for soybean destinedto the grain production (2 stink bugs ≥ 0.5 cm/meter), only two insecticidesapplications during the crop cycle was needed (Table 1).AcademyPublish.org - The Impact of Pesticides173