Effect of insecticides on caterpillar control in soybeans

Soybean cultivation during the 2017/2018 harvest occupied an area of ​​more than 35 million hectares, with production estimated at around 115 million tons (CONAB, 2018). With all this prominence on the world stage, technologies are constantly developed to boost productivity in a sustainable and effective way, focusing on integrated pest management.

The crop yield has increased significantly in the last three decades, due to the combination of the genetic gain of the cultivars and crop management, mainly related to integrated pest management, being a crop quite susceptible to attack by various insects from germination to harvest, and As part of Integrated Pest Management for soybeans, chemical control can be used to minimize damage.

The management of caterpillars and pests in general in soybean crops must take into account several factors regarding sampling, understanding the biology of the pest, control levels and the presence of natural enemies in the system. Chemical control is the method most used by producers, and in this regard, the use of insecticides with proven efficiency in the field is of great importance for successful management.

The area of ​​Intact RR2 soybeans has increased in recent harvests, however Brazil still has a large area of ​​conventional non-Bt soybeans. Two pests stand out in this case, the false caterpillar, Chrysodeixis includens and the Helicoverpa caterpillar, Helicoverpa armigera, which commonly attack the crop at different stages of its development, causing considerable losses to the producer.

Given the problems caused by these pests, the study of new molecules is necessary to minimize damage. Work was carried out with the aim of evaluating the effect of some insecticides on the control of Chrysodeixis includens e Helicoverpa armigera in soybean cultivation, under field conditions.

The experiment was conducted in the experimental area of ​​the Chapadão Agricultural Research Support Foundation – Fundação Chapadão, Chapadão do Sul – MS. The experiment was installed on 18/12/2017 and was carried out until 03/03/2018, when the crop was harvested and the cultural remains were destroyed.

The experimental design was in randomized blocks, with 9 treatments and four replications (36 plots), consisting of 14 crop lines 10 meters long. 60 m treatment². Spacing between crop rows of 0,45m. To apply the treatments, a constant pressure knapsack sprayer (CO₂) with a 3,0 m bar, equipped with 6 Conical jet nozzles, model ATR015, spaced 50 cm apart, at a height of 50 cm from the desired target. Spray volume of 150 L ha^-1, pressure of 3,0 bar.

The treatments consisted of the following active ingredients (dose in g active ingredient): Emamectin Benzoate + OM (7,5 g ha^-1), Emamectin Benzoate + OM (10 g ha-¹), Espinetoram (12 g ha^-1), Chlorfenapyr (192 g ha^-1), Metaflumizone (192 g ha^-1), Indoxacarb (60 g ha^-1), Methomyl+Novaluron (220 + 17,5 g ha^-1) and Thiodicarb (320 g ha^-1).

Assessments were carried out on the plants (“whole”) on 4 meter lines to account for Helicoverpa armigera and the “beating cloth” for counting the number of caterpillars Chrysodeixis includens, in 4 cloth beats per plot, totaling 16 meters evaluated per treatment. A preliminary assessment was carried out to Helicoverpa armigera preceding the applications, and further evaluation at 3, 7, 10 days after the first application and 2, 7, 10 days after the second application. During the evaluations, the false-measure population increased and the evaluation of the pest began using the swab, carrying out 4 swabs per plot.

It was observed that treatments 3 (Emamectin 10 Benzoate), 6 (Metaflumizone) and 7 (Indoxacarb) showed the highest efficiencies in the evaluation 3 days after the 1st application, differing significantly from the control. At 10 days after the first application, treatments 1, 3 (Espinetoram), 4 (Chlorfenapyr) and 5 differed significantly from the control, presenting the highest control means. After the 6nd application, the pest reduced its infestation, without significant differences between the treatments applied, with some caterpillars remaining in the control treatment.

7 days after the first application, infestation of Chrysodeixis includens, with the cloth being beaten for accounting. On this date, it was observed that treatments 3, 4, 5, 8 (Metomil+Novaluron) and 9 (Tiodicarb) had control efficiencies in this pest greater than 80%, differing significantly from the control. After the 2nd application in the 2-day evaluation, it was observed that treatments 3, 5, 6 and 7 showed efficiency greater than 80% of the control, differing significantly from the control. At 7 da2a it was observed that treatment 3 still had an efficiency greater than 90% of control.

The efficiencies over the evaluated dates show some variation for each insecticide, depending on its mode of action. Therefore, the information generated by the work must be analyzed by the producer and adapted to the adopted management.    

Germison Vital Tomquelski, Gustato Ribeiro Camargo, Josiane Oliveira, Claudemir Theodoro and Naiara Luchiari, Chapadão do Sul Agricultural Research Support Foundation - MS