Herbicide Injury in Alfalfa
Herbicide injury in alfalfa can occur in multiple ways such as pesticide particle drift contacting alfalfa foliage, accidental application directly to alfalfa, or persistent herbicide active ingredients present in the soil due to a prior application. There are diverse plant injury symptoms depending on the active ingredient of the herbicide. Symptoms of various herbicide classes are listed here, along with product examples of active ingredients from each:
Amino acid inhibitors (HG 2): reduction in internode length and root mass, yellowing of foliage, leaf veins with reddish discoloration, stunting, slow plant growth, and plant death. Examples: glyphosate and imazamox
Cell growth inhibitors (HG 3 and 15): leaves that are heart-shaped due to midrib shortening, leaf discoloration, plant stunting, brittle and rough stem base, thickened below ground stem and root tissue, and reduced root mass. Examples: trifluralin and chloroacetamide
Cell membrane disruptors (HG 14): bleached spots on foliage and newly formed plant tissue with wrinkling deformation. Example: fomesafen
Growth regulators (HG 4): leaf cupping and strapping, dark green discoloration of plants, stem curling, and root tissue proliferation. Example: 2,4-D
Photosynthetic inhibitors (HG 5): foliage yellowing and death and defoliation. Example: atrazine
Pigment inhibitors (HG 27): bleached foliage with possible reddish border. Example: mesotrione
Pest insects and disease-causing pathogens may cause symptoms similar to herbicide injury. Indications of herbicide injury include patterns that correspond to changes in soil type or the movement of application equipment through a field and, in the case of drift, a reduction in injury symptoms moving away from a drift source.
Herbicide injury in alfalfa caused by prosulfuron (HG 2).
Cal Shumway, Bob Scott, and John Boyd, www.uada.edu
Herbicide injury in alfalfa caused by quinclorac (HG 4).
Cal Shumway, Bob Scott, and John Boyd, www.uada.edu
When applying herbicides, check the label to make sure weather conditions during and after an application are suitable. Clean out spray tanks and hoses after herbicide application, use appropriate spray nozzles, apply correct pesticide rates, and calibrate the sprayer. Make sure soil applied herbicides are adequately incorporated.
Prepared by the Alfalfa Pest Management Working Group.
Herbicide Carryover in Alfalfa
Herbicide injury in alfalfa caused by prosulfuron (HG 2). Cal Shumway, Bob Scott, and John Boyd, www.uada.edu.
Herbicide injury in alfalfa caused by quinclorac (HG 4). Cal Shumway, Bob Scott, and John Boyd, www.uada.edu.
Herbicide injury in alfalfa caused by metribuzin (HG 5). Cal Shumway, Bob Scott, and John Boyd, www.uada.edu.
Herbicide injury in alfalfa caused by cyhalofop (HG 1). Cal Shumway, Bob Scott, and John Boyd, www.uada.edu.
Gallery images courtesy Cal Shumway, Bob Scott, and John Boyd, www.uada.edu.
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