Forestry Herbicide Symptoms & Mode of Action. John Boyd University of Arkansas [email protected] 501-671-2224. What is mode of action?. How a herbicide disrupts or inhibits normal plant development. Examples cell membrane destruction. block protein synthesis
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Phloem mobile herbicides move up and down in the plant
Contact herbicides do not move in the plant
Xylem mobileherbicides move up in the plant
Affect cell division, cell enlargement, protein synthesis and respiration. Act by upsetting hormone balance.
Twisting of stems and leaf cupping are typical symptoms of the growth regulator herbicides.
Deformed pin oak leaf caused by 2,4-D. This is referred to as the drawstring effect.
Vanquish (dicamba) as the drawstring effect.
Upward cupping of leaves on azalea. Common symptom with dicamba exposure.
Upward cupping of leaves on lilac from 2,4-D exposure. dicamba exposure.
These herbicides interrupt photosynthesis the process by which green plants convert light energy into food.
Symptoms often appear on the margins of the oldest leaves (pear).
Karmex (diuron) on oak. Symptoms often appear on the margins of the oldest leaves.
These herbicides cause the green pigments (chlorophyll) in plants to be destroyed. Without chlorophyll, plants cannot photosynthesize and will die.
The root inhibitors interrupt cell division (mitosis) stopping root growth in seedling plants.
Roots on susceptible plants will be stubby and thick, especially lateral roots
Destroy cell membranes, causing cell contents to leak out and result in desiccation of plant tissue.
Paraquat drift on pecan causes speckling of the leaves. especially lateral roots
Fast acting herbicides that produce rapid leaf burn.
These herbicides act by disrupting lipid biosynthesis in grass plants. Plant cells and cellular organelles all contain lipid membranes. Therefore, these herbicides affect cell membrane integrity in the meristems.
Grass herbicides symptoms on johnsongrass especially lateral roots
These herbicides inhibit amino acid synthesis which is necessary for the formation of plant proteins.
Compact growth on azalea
Bunched, compact growth on dogwood and sassafrass
Arsenal symptoms on maple. especially lateral roots
Strapped leaves on maple due to Roundup. exposure.
Roundup drift from the previous fall may cause strapped leaves on peaches, apples and pears the next spring.
Stunted, compact growth due to glyphosate. leaves on peaches, apples and pears the next spring.
Finale (glufosinate) on pine leaves on peaches, apples and pears the next spring.
Terminal damage from a tank mix of Accord + Arsenal leaves on peaches, apples and pears the next spring.