Evaluation of New Herbicides on the Physiological Response and Control of Chrozophora (Chrozophora rottleri)

Abstract— Chrozophora rottleri is an aggressive, competitive broadleaf weed commonly found in rainfed and irrigated cropping systems. Its rapid growth and high resource consumption significantly reduce the growth and productivity of main crops. Effective management requires a thorough understanding of how different herbicides affect its physiological processes. A field experiment was conducted during the Rabi season of 2014-15 at the Regional Agricultural Research Station (RARS), Lam Farm, Guntur. The study employed a Randomized Block Design (RBD) with ten herbicidal treatments: atrazine, alachlor, pendimethalin, 2,4-D Na salt, bispyribac, pyrithiobac, topramezone, Iris (a.i. mesosulfuron-methyl + iodosulfuron-methyl), ethoxysulfuron, and an untreated control. Herbicides were applied at their recommended field doses, and physiological observations were recorded at 14 and 21 Days After Sowing (DAS). Parameters assessed included plant height, leaf area, total chlorophyll content, photosynthetic rate, stomatal conductance, transpiration rate, and phytotoxicity symptoms. Results revealed significant variation among treatments for all measured traits. The untreated control showed the highest plant height (24.53 cm) and substantial leaf area (1141.0 cm²), indicating vigorous growth in the absence of herbicide stress. These values were statistically on par with those observed in plots treated with pendimethalin and pyrithiobac, suggesting minimal growth suppression by these herbicides. Chlorophyll content was highest in the control (1.375 mg g⁻¹ fresh weight), followed closely by pendimethalin (1.352 mg g⁻¹) and bispyribac (1.348 mg g⁻¹). In stark contrast, topramezone (0.642 mg g⁻¹) and ethoxysulfuron (0.0 mg g⁻¹) caused severe chlorophyll degradation. Interestingly, photosynthetic rate was highest under alachlor (51.93 µmol m⁻² s⁻¹) and bispyribac (50.91 µmol m⁻² s⁻¹), while ethoxysulfuron completely inhibited photosynthesis. Phytotoxicity was most severe with ethoxysulfuron (score 10) and topramezone (score 9), causing plant mortality, whereas pendimethalin and pyrithiobac showed minimal visible injury (score 0). The study concludes that pendimethalin and pyrithiobac exert limited suppressive effects on the physiology of C. rottleri, while ethoxysulfuron and topramezone are highly effective and phytotoxic, causing complete physiological shutdown and plant death. These findings provide critical physiological insights for designing integrated and targeted weed management strategies against this problematic weed under field conditions.