Herbicide Modes of Action & Applications – 100+ Q&A | ALS Inhibitors, Photosynthesis Blockers, ACCase Inhibitors

This expertly structured study guide includes 100+ fully solved Q&A items focusing on herbicide biochemical modes of action, translocation, application techniques, and target plant effects, tailored for the 2025/2026 academic year. It is ideal for students in agronomy, weed science, crop protection, plant physiology, and agricultural biotechnology, and also supports preparation for pesticide applicator certification exams and academic assessments. Detailed by herbicide active ingredient, this resource covers: Site and mode of action: ALS (acetolactate synthase) inhibitors (e.g., Halosulfuron, Imazapyr), EPSP synthase inhibitors (e.g., Glyphosate), ACCase inhibitors (e.g., Sethoxydim, Fluazifop), and Photosystem I & II inhibitors (e.g., Atrazine, Diquat, Paraquat) Translocation pathways: symplastic (e.g., Glyphosate, Imazapyr), apoplastic (e.g., Atrazine, Bentazon), and non-translocated herbicides (e.g., Diquat, Paraquat) Application types: foliar vs. soil-applied herbicides, with specific crop-based use cases for atrazine, clomazone, halosulfuron, and trifluralin Chemical families and resistance risks: triazines, phenoxies, sulfonylureas, thiocarbamates, diphenylethers, and dinitroanilines; includes insights into cross-resistance, volatility, and tank-mix considerations Effect on plants: unregulated auxin responses (e.g., 2,4-D), inhibition of amino acid or fatty acid synthesis, reactive oxygen species (ROS) generation, and disruption of microtubule assembly (e.g., Pendimethalin, Trifluralin) Practical weed management integration: pre- and post-emergence use, selectivity for broadleaf vs. grassy weeds, and application in corn, sorghum, peanuts, beans, turf, and vegetable crops This guide provides the molecular understanding and practical framework required for students and professionals dealing with herbicide classification, efficacy, and resistance management. Keywords: herbicide modes of action, ALS inhibitors, ACCase inhibitors, Photosystem I inhibition, Photosystem II inhibition, EPSP synthase, symplastic translocation, apoplastic movement, foliar herbicide, soil-applied herbicide, reactive oxygen species, auxin mimic, triazine herbicides, glyphosate mode of action, bentazon, imazapyr, halosulfuron, metolachlor, trifluralin, weed resistance, pesticide certification