Managing Palmer Amaranth in Central Arizona Cotton: A Stakeholder-Driven Herbicide Evaluation
Agronomy & Pest Management
Avik Mukherjee
Assistant Extension Agent, Agronomy
University of Arizona
Casa Grande
Abstract
Herbicide-resistant Palmer amaranth (Amaranthus palmeri) continues to pose a serious challenge to cotton production in Arizona, where resistance to multiple herbicide sites of action, including glyphosate and acetolactate synthase (ALS) inhibitors, has been widely reported. A recent needs assessment survey conducted in Pinal County (the highest cotton-producing county in Arizona) indicated strong stakeholder demand for updated weed management information: 65% of respondents sought guidance on chemical weed control, and 79% expressed interest in herbicide efficacy data for cotton production systems. In response to these identified needs, a stakeholder-driven field study was conducted to evaluate the performance of selected pre- and post-emergence herbicide programs for Palmer amaranth management under the arid conditions of Central Arizona. Field experiments were carried out at the University of Arizona Maricopa Agricultural Center using Enlist- and dicamba-trait cotton cultivars in a randomized complete block design with four replications. Herbicide treatments included labeled combinations of glyphosate, glufosinate, pendimethalin, acetochlor, carfentrazone, pyroxasulfone, diuron, and 2,4-D choline. Weed control efficacy was assessed through visual suppression ratings, biomass reduction, and plant height measurements up to four weeks after application. Results demonstrated that integrated herbicide programs combining multiple sites of action provided greater Palmer amaranth suppression than single-mode approaches. These findings provide stakeholder-informed, regionally relevant recommendations that support herbicide stewardship, help mitigate resistance development, and improve the sustainability of cotton production in Arizona’s low-desert agricultural systems.
Authors: Avik Mukherjee, Bhupinder Singh, Randy Norton
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Avik Mukherjee Assistant Extension Agent, Agronomy, University of Arizona, Arizona, 85122
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Bhupinder Singh Assistant Professor and Extension Specialist, University of Arizona, Arizona, 85138
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Randy Norton Extension Agronomist and Director, University of Arizona, Arizona, 85546