Cultural practices to reduce damage by borer insects in commercial cultivars of Amaranthus

Abstract

Stem borer insects are one of the most important pest groups of Amaranthus crops on a global scale. In this study, we evaluated the magnitude of borer herbivory in five cultivars of Amaranthus experimentally in La Pampa, Argentina, during two growing seasons. We tested the effect of several plant attributes of five cultivars of Amaranthus on the herbivory caused by three stem borer species. In turn, we evaluated the effect of cultivar and plant density (both as factors modifying the thickness of the stems) and the effect of cultivar and planting time (both as factors modifying the length of the life cycle of the plants) on the herbivory caused by the stem borers in two cultivars of Amaranthus hypochondriacus. We report a wide variation in the susceptibility of the cultivars to stem borer herbivory and discuss the effects of the plant features investigated. Phenological and morphological features of the stems (especially the diameter) influenced the selectivity of host plants by the adult females. The management practices tested here, including plant density and sowing date manipulations, modified plant structure and consequently influenced the damage by stem borers. High density sown plants presented thinner stems and suffered reduced damage by borers than plants sown at low density, whereas delayed sown plants had thinner stems and were less attacked by borer insects than earlier sown plants. The implementation of these cultural practices seems to be a promising alternative for the management of borer species, to which Amaranthus is particularly vulnerable.