Investigations of the allelopathic effects of palmer amaranth (Amaranthus palmerı S. watson) between some weed species and crops

Aim: In these studies it was aimed to determine allelopathic effects of Amaranthus palmeri which is an invasive plant introduced to Turkish flora in 2016 was investigated on cotton, maize, sunflower and tomato as well as on some weed species. Furthermore control of this weed by means of allelopathic effects of some Brassicaceae species was investigated. Materials and Methods: Petri, pot and field studies were conducted. Cotton, maize, sunflower and tomato were used as crop species and Amaranthus retroflexus L, Echinochloa crus-galli (L.) P. Beauv., Amaranthus palmeri, Portulaca oleracea L. and Solanum nigrum L. were used as weeds. In the studies aiming the control of A. palmeri different radish species were used belonging to Brassicaceae family. With petri studies the effect of aqueous extracts at different concentrations (1, 2, 4, 8 and 16%) was investigated on the germination of crop and weed seeds. In pot experiments the effects of powder extract was investigated on the growth of crops and weeds at different concentrations (1, 2, 3, 4 and 5%). In field experiments the effects of A. palmeri residues on the growth and yield of crops as well as on the emergence of weed seeds was investigated. Results: In petri studies A. palmeri extract reduced the germination of all seeds and the reduction was higher as the dose increased. At highest dose cotton was the most resistant while tomato was the most sensitive species. Weeds were in general more sensitive to aqueous extract than crops. At the highest concentration growth of weeds were suppressed by 87-100% depending on the species. In pot experiments growth of all crops and weeds were suppressed by A. palmeri powde extract depending on the dose. At highest dose cotton and tomato was the most sensitive (≥%90) while maize and sunflower was affected less (≤%70). In the case of weeds, S. nigrum, A. retroflexus and A. palmeri were the most sensitive weed species. In field experiments, it was observed that yield parameters of cotton, tomato and corn, which are the most adversely affected crop plants, decreased by 38% and above in all parameters studied from A. palmeri residues, while it did not affect sunflower. Also in this study, as a result of petri and pot experiments carried out using little radish, turnip and garden radish from the Brassicaceae family with has allelopathic content for the management of A. palmeri, effects were seen up to 100% and it was determined that the most effective radish was turnip, but the effect of garden and little radishes was close to turnip. Conclusion: Results of these studies showed that A. palmeri has highly damaging potential to crops due to its allelopathic content. Similarly high effects of extracts on weeds implicate the importance of allelopathy in the invasion success of this weed. On the other hand high efficacy against weed species can be considered as potential source for a bioherbicide. Results of the studies showed also that some Brassicaceae plants can be used for in the control of A. palmeri.