Response of weedy sunflower populations (Helianthus annuus L.) to imazamox and nicosulfuron

Abstract

Weedy sunflower, Helianthus annuus L. is an economically very important, invasive species widely distributed in many regions of the world, especially in the areas where sunflower hybrids tolerant to some als-inhibiting herbicides are intensively cultivated. The discovery and development of a new technology in cultivated sunflower increased the emergence of resistant biotypes due to high selection pressure and spontaneous hybridisation (transfer of genes responsible for tolerance from crop to wild species). This study examined the responses of two populations of weedy sunflower (HELAN 1 and HELAN 2) to nicosulfuron and imazamox in bioassay under greenhouse conditions. The experiment included five treatments with different application rates of imazamox (12, 24, 48, 96 and 192 g ha-1) and nicosulfuron (10, 20, 40, 80 and 160 g ha-1) that were applied over plants at their growth stage of 2-3 pairs of developed leaves. In addition to the visual assessment of plant damage, which was performed 7, 14, 21 and 28 days after the herbicide application, the following parameters were also measured: fresh and dry weight. The obtained results indicate changes in the sensitivity of the examined weedy sunflower populations to als inhibitors. Reduced sensitivity of the HELAN 1 to imazamox and HELAN 2 to nicosulfuron suggests a possible development of resistant populations of weedy sunflower in the Surčin area.