Strategies that guarantee efficiency in the management of whitefly in soybeans

Soybean productivity (Glycinemax L.Merril) is influenced by several factors such as soil, climate, rainfall, occurrence of pests and diseases. Among the various pests that occur in soybean crops, the whitefly (Bemisia tabaci biotype B) has increased in frequency in soybean crops across the country (Luttrell, 1994). The high incidence of whiteflies is due to the expansion of the soybean planting area, the extension of the sowing season and the successive and staggered cultivation of the crop, using a central pivot. The whitefly attacks several crops, sucks their sap, causes changes in vegetative and reproductive development, with wilting, leaf fall and fruit loss (Alencar) et al., 1998). Work on soybean crops shows that coexistence with an average of ten nymphs per leaf led to losses of around 12 bags per hectare (Tomquelski; Martins; Dias, 2015).

It is recommended, within chemical management, the alternation of products with different modes of action, for sustainable management and to reduce the probability of evolution of drug resistance. B. tabaci to the products used in its control. In chemical control, products that induce behavioral changes through repellency or irritation, growth-regulating insecticides and insecticides that act on the nervous system, such as neonicotinoids, have been used (Basu, 1995). Given the few insecticides with different chemical groups and mode of action used for its control, the registration of new molecules and mixtures of existing active ingredients is an important strategy to guarantee the efficiency of controlling this pest in the most diverse crops.

The molecules flupyradifurone and spiromesifen have low toxicology and ecotoxicology, presenting an excellent toxicological profile to be integrated into integrated pest management programs. Furthermore, the two molecules control whiteflies in the nymph stages up to the third instar (Nicolaus et al., 2005; Nauen et al., 2015) and adults. Spiomesifen inhibits lipogenesis through its effect on acetyl CoA-carbolxylase (Nauen et al., 2003), and flupyradifurone is a systemic insecticide that belongs to a new chemical class, butenolide, acting as a competitive modulator of nicotinic acetylcholine receptors (Irac, 2020). Flupyradifurone can be used in different crops via foliar, seed and furrow treatment, in addition to being considered a new resistance management tool for various targets in different crops, due to its effectiveness against sucking insects resistant to other groups such as neonicotinoids and pymetrozine (Bayer, 2013).

Experiment

The present work aimed to evaluate the effectiveness of the insecticide flupyradifurone 120g a.i./kg + spiromesifen 120g a.i./kg in the control of whiteflies in soybean crops, using the BMX Garra RR variety. The experiment was conducted under field conditions, at the School Farm of the State University of Londrina (UEL), located on Rodovia Celso Garcia Cid, km 380, city of Londrina, Paraná, between the months of February and May 2017; in clayey soil (73%). The experimental design was in randomized blocks, with six treatments and four replications. In addition to the control, the treatments were composed of the insecticides flupyradifurone 120g a.i./kg + spiromesifen 120g a.i./kg at 0,8; 1,0; 1,2 and 1,4 kg/ha; pyriproxyfen 100g/L + xylene 800g/L (standard) at 0,25L/ha. Two applications were carried out, seven days apart, at BBCH stages 60 and 65.

Applications were carried out using a constant pressure knapsack sprayer, propelled by pressurized CO2, using six model 110.015 flat jet spray nozzles, spaced every 0,4m, with a working pressure of 2,5bar and a volume of spraying of 200L/ha. Each experimental plot was 5m long and 4m wide, totaling 20m², with a spacing of 45cm, 8cm between plants, five streets per plot and a density of 12 plants per linear meter. The agronomic efficacy evaluations of the treatments were carried out at 4, 7 DAA and 1, 3, 7, 10 DAB (days after the first and second application), following a count of the number of insects in ten leaflets per plot, and subsequently these information was transformed into Abbott percentage.

The behavior of the adult insect makes assessments difficult, as it is a migratory insect, consequently assessments of nymphs are used to prove effectiveness. To quantify the selectivity of treatments to the crop, phytotoxicity assessments were carried out on soybean plants. Productivity was also evaluated, which was quantified at 74 DAB, through the harvest of 7,5m²/plot (kg). The data obtained were subjected to analysis of variance, and the treatment means were compared using the Tukey test at a 5% probability level (Table 1).

Under the conditions under which the experiment was conducted, it was possible to observe control of nymphs from 4 DAA in treatments using flupyradifurone 120g a.i./kg + spiromesifen 120g a.i./kg at doses of 1,0, 1,2 and 1,4 kg/ha , with efficacy ranging from 82,3% to 95%. These doses remain higher than the standard from the first assessment until the assessment carried out at 10 DAB, when they achieve control ranging between 98,4% and 99,1%. From 7 DAB onwards, flupyradifurone 120g a.i./kg + spiromesifen 120g a.i./kg shows an efficacy of 97,7% at the lowest dose: 0,8kg/ha (Figure 1). 

The insecticide flupyradifurone 120g a.i./kg + spiromesifen 120g a.i./kg did not cause any signs of phytotoxicity in soybean crops, regardless of the dose. In relation to productivity, all treatments were statistically superior to the control, with flupyradifurone 120g a.i./kg + spiromesifen 120g a.i./kg at 0,8; 1,0; 1,2 and 1,4 kg/ha generated an increase in productivity of 14,3% to 40,8% (Figure 2). It is concluded that flupyradifurone 120g a.i./kg + spiromesifen 120g a.i./kg at doses of 0,8, 1,0, 1,2 and 1,4 kg/ha is efficient in controlling whitefly and selective for whitefly culture. soy.

 

Yuri Ramos, J. N Della Valle, F. Sulzbach, A. C. A. Krol, T. Docema, M. M. Martins, M. A. N. Nishikawa and D. M. Okuma, Bayer