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. Afield 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 Nasalt, 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.
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Introduction
Chrozophora rottleri is a troublesome broadleaf weed prevalent in both rainfed and irrigated agricultural ecosystems across India. Its competitive ability for essential resources—light, nutrients, and water—poses a significant threat to crop yields. Effective and timely weed management is therefore paramount for sustainable crop production and resource use efficiency. Among various control methods, chemical weed control via herbicides remains a cornerstone due to its efficacy, timeliness, and economic feasibility. However, herbicide effectiveness is highly variable, depending on factors such as the weed species, its growth stage, the herbicide'smode of action, application rate, and environmental conditions. Furthermore, non-target effects and the potential for developing herbicide resistance necessitate a judicious and science-based selection of herbicides (Chauhan & Abugho, 2013). Traditional herbicides like atrazine, alachlor, pendimethalin, 2,4-D, and newer molecules like bispyribac and pyrithiobac have been widely used for broad-spectrum weed control. Concurrently, newer herbicides such as topramezone (an HPPD inhibitor), ethoxysulfuron (an ALS inhibitor), and pre-mixes like Iris (mesosulfuron-methyl + iodosulfuron-methyl) are being introduced. However, their specific physiological impact and efficacy on Chrozophora rottleri are not well-documented, particularly under field conditions in the Indian context. A detailed understanding of how these herbicides affect key physiological processes— photosynthesis, pigment synthesis, and transpiration—is crucial for predicting their efficacy and understanding the basis of weed susceptibility or tolerance (Grossmann & Ehrhardt, 2007; Heap, 2022).
This investigation was undertaken with the objective of evaluating the effect of a range of pre-and post-emergence herbicides on the growth and physiological performance of Chrozophora rottleri. The specific aim was to identify herbicides that effectively disrupt its physiology, leading to control, while also assessing their degree of phytotoxicity to understand their potential fit within integrated weed management (IWM) programs.
Conclusion
The study conclusively demonstrates that herbicides have a differential and significant impact on the physiology of Chrozophora rottleri. Pendimethalin and pyrithiobac had minimal suppressive effects on growth and physiological functions, indicating that C. rottleri may possess tolerance or that these herbicides are not optimal for its post-emergence control. In contrast, ethoxysulfuron and topramezone were highly effective, causing severe physiological disruption—complete inhibition of chlorophyll synthesis, photosynthesis, and transpiration—leading to high phytotoxicity and plant mortality. Alachlor and bispyribac, while not severely inhibiting growth, showed interesting effects on gas exchange parameters that warrant further investigation. For effective integrated management of Chrozophora rottleri infield crops, post-emergence application of ethoxysulfuron or topramezone can be highly effective. However, their potential crop phytotoxicity must be carefully considered. Pendimethalin, if used, must be applied as a pre-emergence herbicide for effective control. These physiological insights provide a scientific basis for selecting and rotating herbicides in IWM strategies to manage this competitive weed sustainably. CONFLICT OF INTEREST The authors declare no conflict of interest.
