Competition of Palmer amaranth at different densities with cotton in Turkey

Amaranthus palmeri is an invasive weed that was newly introduced to the agricultural fields of Turkey. However, no information exists in the literature about Amaranthus spp.'s competition with cotton in our country. This study assessed its competitive ability with cotton (Gossypium hirsitum) in the Aegean Region in 2020-2021. In pot experiments, the effect of A. palmeri competition was investigated at two stages: early (sowing weed seed with cotton seeds) and later (similar to at 4-6 leaf stages of cotton). Three different A. palmeri densities (1, 2 and 4 per pot) were used in pot experiments. Field experiments were also conducted to assess early A. palmeri interference in cotton with the same weed densities per one-meter row. Pot experiments showed that early competition caused a higher decrease in cotton height and dry weights compared to late competition. On the contrary, A. palmeri's dry biomass was reduced more when seeded in the late stage of cotton with the contribution of intraspecific competition. Regarding the field experiments, height, node number, boll number and yield of cotton significantly decreased with increasing A. palmeri densities. Even one A. palmeri per meter cotton row resulted in significant yield reductions. The yield decreased by 39%-51%, 51%-63% and 79%-75% with the densities of 1, 2 and 4 A. palmeri per one-meter row in 2020 and 2021 respectively. These results showed that A. palmeri is a troublesome weed, causing considerable reductions in cotton growth and yield. Therefore, management strategies for this weed should be implemented.