Abstract
Stink bugs are a major concern for pest management in soybean crops. With agricultural frontiers expanding in Brazil and cultivation techniques being heavily intensified, stink bug populations have become increasingly dispersed and hard to control, causing severe economic losses to soybean growers across the country. Chemical insecticides known as neonicotinoids, organophosphates and pyrethroids currently represent the main control strategy for this pest, being often mixed together in order to enhance control efficacy and prevent resistance development. Each of these chemical groups is characterized by a different mode of action inside the insect’s body, which determines if the insecticide will provide a fast knockdown effect or a long residual control effect. The aim of this work was to evaluate the knockdown and residual control effects delivered by these groups of insecticides under field conditions and during two cropping seasons, both in isolated and combined use, determining the most efficient strategy for chemical management of stink bugs on soybean crops. The pyrethroid lambda-cyhalothrin (250 g L-1) had the best knockdown effect, while the neonicotinoid imidacloprid (700 g kg-1) provided the longest residual control. The highest control efficacy was obtained with the combination of lambda-cyhalothrin + thiamethoxam (106 + 141 g L-1), which resulted in 84.8% of stink bug control.
Highlights
The phytophagous stink bugs (Hemiptera: Pentatomidae) found in the soybean crop are considered pests of great economic importance in many countries (Panizzi & Slansky, 1985; Corrêa-Ferreira, Krzyzanowski, & Minami, 2009). The relevance of these insects has increased in recent years due to several reasons, such as the expansion of area grown with soybean, variation in the sowing dates and other crops serving as hosts for the pest (Panizzi & Grazia, 2001), increase of the reproductive period in modern soybean cultivars resulting in higher food offer to the insect, and reduction in the use of insecticides in Bt soybean cultivars (Guedes et al, 2016)
Chemical control is the most usual strategy for stink bug management in soybean crops, and the chemical insecticide groups used are restricted to the neonicotinoids, organophosphates and pyrethroids, in a total of 20 active ingredients registered in the Brazilian Ministry for Agriculture (AGROFIT, 2018)
Several pyrethroids and neonicotinoids are often used together in commercial mixtures due to the complementarity of effects between them, the first causing immediate knockdown and the second offering a long residual control, characteristics that are determined by their modes of action (Sosa-Gómez & Omoto, 2012)
Summary
The phytophagous stink bugs (Hemiptera: Pentatomidae) found in the soybean crop are considered pests of great economic importance in many countries (Panizzi & Slansky, 1985; Corrêa-Ferreira, Krzyzanowski, & Minami, 2009). The relevance of these insects has increased in recent years due to several reasons, such as the expansion of area grown with soybean (currently reaching 35 million hectares in Brazil; CONAB, 2018), variation in the sowing dates and other crops serving as hosts for the pest (Panizzi & Grazia, 2001), increase of the reproductive period in modern soybean cultivars resulting in higher food offer to the insect, and reduction in the use of insecticides in Bt soybean cultivars (Guedes et al, 2016). Several pyrethroids and neonicotinoids are often used together in commercial mixtures due to the complementarity of effects between them, the first causing immediate knockdown and the second offering a long residual control, characteristics that are determined by their modes of action (Sosa-Gómez & Omoto, 2012)
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