Assessment of weed control efficiency of pyrithiobac sodium and its influence on growth, physiology and yield parameters of cotton (Gossypium hirsutum L.)

Abstract

Cotton ( Gossypium hirsutum L.) is one of the vital fiber crops worldwide. Its production is adversely affected by several weeds, causing substantial phytotoxicity to crop growth and development. Effective and safe herbicide options are needed to manage dominant broadleaf weeds without compromising crop performance. This study evaluated the efficacy of a pre-and post-emergence herbicide, pyrithiobac sodium, against some major broadleaf weeds. In pots, applications were made at different weed growth stages, with and without adjuvant. In field plots, early- and mid-stage applications were tested at varying doses. Crop injury, weed biomass reduction, growth parameters, yield traits, and oxidative stress markers (antioxidant enzymes, ROS, and MDA) were assessed at multiple time points. In pots, the herbicide achieved complete control of Solanum nigrum at the 4-leaf stage, while control efficacy at the 5-leaf stage ranged from 91–95%, but this dropped to 80–85% by the 6-leaf stage. Temporary leaf injury appeared on cotton soon after spraying, yet plants later recovered fully. In field plots, pyrithiobac sodium lowered biomass of S. nigrum and Amaranthus retroflexus by up to 86.8% and 89.3%. Although over 80% of cotton plants showed noticeable injury within the first week, symptoms fell below 5% by day 42. However, the maximum dose (274.2 mLha⁻1) notably suppressed plant height, biomass, chlorophyll, boll count, and seed cotton yield. Early-stage application resulted in significant reductions in growth and yield-related parameters, whereas mid-stage applications showed comparatively smaller and, in some cases, non-significant effects. This was accompanied by marked increases in antioxidant enzymes (POD, SOD, APX, CAT), reactive oxygen species (H 2 O 2 and O 2 ⁻), malondialdehyde content, and electrolyte leakage, especially with the highest dose applied at the early stage. These results indeed highlight the practical implications of optimizing both the timing and dose rate of herbicide application to reduce physiological stress in cotton plants while ensuring effective weed management.