Reaction of two growth types of pinto beans (Phaseolus vulgaris L.) to weed management

Bean is one of the most important legumes worldwide for direct human consumption and is a rich source of protein and carbohydrates. Bean is weak to compete with weed because of the slow growth at the early stages. Therefore, competition with weeds causes a significant reduction in grain yield at the end of the growing season. Weed competition is a kind of nonliving stress, which effect on plant yield. Pinto bean (Phaseolus vulgaris L.) cultivars, with different morphological and genetic characteristics, show different responses in the presence of weeds, which may ultimately result in possible difference in yield. The purpose of this research is to evaluate the effect of different chemical and non-chemical weed control managements on the yield of determinate and indeterminate bean varieties.

A field experiment was carried out in Behshahr, Mazandaran, in 2021. The experiment was conducted as factorial based on a randomized complete block design with three replications. The first factor: different weed control methods (1) trifluralin herbicide as pre-sowing 2.5 liters per hectare; (2) Trifluralin herbicide 2.5 liters per hectare + one weeding stage; (3) wheat mulch in the amount of two tons per hectare; (4) bentazon 50% of the recommended dose; (5) bentazon 75% of the recommended dose; (6) bentazon 100% of the recommended dose; (7) weed-free control; (8) control with weed and the second factor includes bean cultivars: (1) Sadri variety (indeterminate growth type) and (2) Negin variety (determinate growth type). In the final harvesting stage, the type of weed species, density, and dry weight of weeds were measured. Also, SPAD value, height, number of pods per plant, number of sub-branches, number of leaves per plant, number of seeds per pod, weight of 100 seeds, seed yield and biological yield of pinto beans were investigated.

The results showed that Amaranthus retroflexus L. and Portulaca oleracea L. had the highest relative frequency in the field. The highest density and dry weight of weeds were observed in the weed infestation control treatment, and among the weed management treatments, mulch and bentazon 100% of the recommended dose treatments caused a decrease in the density and dry weight of weeds in Negin and Sadri cultivars. Among the weed management treatments, the highest height, number of leaves, number of pods per plant, 100-seed weight, seed yield and biological yield were observed in mulch and bentazon 100% of the recommended dose treatment. The use of trifluralin and bentazon 50% treatments had the least effect in controlling weeds. The highest amount of seed yield of Sadri variety (2426.01 kg.ha-1) and Negin variety (1957.11 kg.ha-1) was observed in the weed-free control treatment. Sadri variety with indeterminate growth has higher competitive ability with weeds and had higher yield than Negin variety.

In general, it can be concluded that the Sadri cultivar with higher competitive ability and having morphological and physiological characteristics had performed better against the weed than the Negin cultivar and also, among the weed management treatments, the non-chemical treatment of mulch and the chemical treatment of bentazon 100% of the recommended dose had better performance.