Due to the length of egg-laying period (> 80 days), two applications of insecticides against cabbage stem weevil (Ceutorhynchus pallidactylus Marsh.) are currently needed. However, resistance of pollen beetle (Brassicogethes aeneus F.) to pyrethroids complicates the choice of suitable insecticide for the second application. The active ingredients cypermethrin, etofenprox, pymetrozine, indoxacarb and chlorpyrifos-ethyl applied as second spring applications to winter oilseed rape crops were assessed under field conditions from 2016 to 2018 to ascertain how they could reinforce the effects of the first spring application (beta-cyfluthrin) on cabbage stem weevil. Chlorpyrifos-ethyl and etofenprox strengthened the effects of the first spring spray on cabbage stem weevil markedly more than cypermethrin. Pymetrozine and indoxacarb, effective on resistant populations of pollen beetles, showed the lowest contribution to increase the effects. Indoxacarb showed a low effect on C. pallidactylus in laboratory tests too. The impacts of the bans on active ingredients chlorpyrifos-ethyl and pymetrozine are discussed.
Bruchus pisorum L., is an economically important pest of field pea (Pisum sativum L.) crops worldwide, however, no fully effective methods (conventional, alternative) of its control exist now. To fill this knowledge gap, possibilities of trap cropping were tested in the years 2015–2017. Two field pea varieties differing in the start of flowering, and one spring barley variety, were used to design four different types of crops, that were compared in large plot trials (2.82 ha). It was hypothesized the females would prefer zones planted with early flowering variety for oviposition. In all three seasons, females placed more eggs on pods in the parts of plots planted with the early flowering variety, and positive aggregation of the eggs and infested seeds were recorded there too. In cases where the egg-laying period is shorter than 14–21 days, the early flowering variety located at the margins should serve efficiently as a trap crop.
A total of 251 pollen beetle (Brassicogethes aeneus F.) populations sampled in the Czech Republic and Slovakia were tested against both lambda-cyhalothrin and tau-fluvalinate by means of Insecticide Resistance Action Committee (IRAC) susceptibility test method 11, version 03 (glass vial test) over four (2015-2018) years. The results confirmed high levels of resistance to lambda-cyhalothrin in the pollen beetle populations of both countries. Tau-fluvalinate is less affected by resistance, but relatively high proportions of resistant populations at many localities in both countries make this insecticide almost unusable against the pest too. The results of a correlation analysis of lethal concentration (LC) values (LC 50 and at least partly of LC 90 values, too) indicate a moderate level of cross resistance against the two active ingredients in Czech populations. In Slovakian populations, the positive correlation between the LC 50 values proved to be significant only in 2018 (r = 0.66, p < 0.001). Despite certain variability in the results of the correlation analysis recorded in this study, the findings indicate another possible decrease in the susceptibility of pollen beetles to pyrethroids, in general, if tau-fluvalinate were used for their control under field conditions.
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