Very long chain fatty acid–inhibiting herbicides: Current uses, site of action, herbicide-resistant weeds, and future

Abstract

The herbicides that inhibit very long chain fatty acid (VLCFA) elongases are primarily used for residual weed control in corn, barley, oat, sorghum, soybean, sugarcane, certain vegetable crops, and wheat production fields in the United States. They act primarily by inhibiting shoot development of susceptible species, preventing weed emergence and growth. The objectives of this review were to summarize (1) the chemical family of VLCFA-inhibiting herbicides and their use in the United States, (2) the VLCFA biosynthesis in plants and their site of action, (3) VLCFA-inhibitor resistant weeds and their mechanism of resistance, and (4) the future of VLCFA-inhibiting herbicides. After their re-classification as group 15 herbicides to include shoot growth-inhibiting herbicides (group 8), the VLCFA-inhibiting herbicides are currently represented by eight chemical families (benzofurans, thiocarbamates, α-chloroacetamides, α-oxyacetamides, azolyl-carboxamides, isoxazolines, α-thioacetamides, and oxiranes). On average, VLCFA-inhibiting herbicides are applied once a year in both corn and soybean in the United States with acetochlor and S-metolachlor being the most-used VLCFA-inhibiting herbicides in corn and soybean, respectively. The site of action of group 15 herbicides results from inhibition of the VLCFA synthase, encoded by several fatty acid elongase (FAE1)-like genes in VLCFA elongase complex in an endoplasmic reticulum. The VLCFA synthase is a condensing enzyme, and relies on a conserved, reactive cysteinyl sulfur in active site that performs a nucleophilic attack on either the natural substrate (fatty acyl-CoA) or the herbicide. As of August 2023, 13 weed species have been documented resistant to VLCFA-inhibitor, including 11 monocot weeds and two dicot weeds (Palmer amaranth and waterhemp). The isoxazolines (pyroxasulfone and fenoxasulfone) are the most recently (2014) discovered VLCFA-inhibiting herbicides. Although the intensity of VLCFA-inhibitor-directed discovery efforts has decreased over the past decade, this biochemical pathway remains a viable mechanistic target for the discovery and valuable component of herbicide premixes.

Crop safety and control of acetolactate synthase inhibitor-resistant Palmer amaranth (Amaranthus palmeri) with very long-chain fatty acid-inhibiting herbicides in dry edible bean

“…Very long chain fatty acid (VLCFA)-inhibiting herbicides, categorized under Weed Science Society of America (WSSA) Group 15 herbicides, are integral components of sequential PRE fb POST programs, providing effective control of several herbicide-resistant pigweed species (Steckel et al, 2002;Jhala et al, 2015;Chahal et al, 2018;Goodrich et al, 2018;Miranda et al, 2022b). Pigweed species often exhibit resistance to multiple herbicide modes of action, making the evaluation of VLCFA-inhibiting herbicides critical (Jhala et al, 2024) These herbicides, including dimethenamid-P, S-metolachlor and pyroxasulfone, offer a potential solution for effective season-long control of Palmer amaranth in dry edible beans (Wilson and Sbatella, 2014;Soltani et al, 2018b). They have demonstrated efficacy against a broad spectrum of weeds, including grass weeds, nutsedges, and small-seeded broadleaf weeds such as pigweed species, including those resistant to glyphosate, ALS, and PSII inhibitors, across multiple crops (Soltani et al, 2006;Mueller and Steckel, 2011;Li et al, 2017Li et al, , 2014bStephenson et al, 2017).…”

“…While instances of resistance to VLCFA inhibitors have been reported less frequently than with glyphosate, ALS inhibitors, and PSII inhibitors, the rising occurrence of resistance, particularly in waterhemp and Palmer amaranth, underscores the urgency for proactive resistance management strategies. The increasing trend of resistance requires diligent surveillance and the implementation of integrated weed management approaches to maintain the effectiveness of these herbicides in crop protection (Jhala et al, 2024).…”