herbicide mode of action chart herbicide mode of action summary

Understanding the mode of action of herbicides is crucial for effective weed management in agricultural settings. With numerous herbicides available, each with its unique mechanism of controlling weeds, a comprehensive herbicide mode of action chart can help farmers, agronomists, and pest control professionals make informed decisions. The mode of action refers to the specific biological process or mechanism through which a herbicide exerts its effect on weeds. Here are key points to consider about different herbicides based on their modes of action:

1. Inhibition of Acetolactate Synthase (ALS)

Herbicides that inhibit acetolactate synthase (ALS) are widely used for controlling a broad spectrum of weeds. ALS is an enzyme essential for the synthesis of branched-chain amino acids in plants. By inhibiting this enzyme, ALS-inhibiting herbicides prevent the production of these amino acids, which are vital for plant growth. This mode of action is common in many sulfonylurea and imidazolinone herbicides, making them effective against a wide range of weed species.

2. Inhibition of Acetyl-CoA Carboxylase (ACCase)

Herbicides that inhibit acetyl-CoA carboxylase (ACCase) are another important class, primarily used to control grassy weeds. ACCase is an enzyme crucial for the synthesis of fatty acids in plants. Inhibition of this enzyme disrupts lipid synthesis, leading to the death of susceptible weeds. Herbicides with this mode of action, such as those in the aryloxyphenoxypropionate (FOP) and cyclohexanedione (DIM) chemical families, are widely used in cereal crops and turf.

3. Inhibition of Protoporphyrinogen Oxidase (PPO)

Herbicides that inhibit protoporphyrinogen oxidase (PPO) are used for pre-emergence and post-emergence control of broadleaf and grassy weeds. PPO is an enzyme involved in the synthesis of chlorophyll. Inhibiting this enzyme leads to the accumulation of a phototoxic intermediate, which causes cell death when exposed to light. PPO inhibitors, such as diphenyl ethers and oxadiazoles, are effective against a wide range of weed species.

4. Inhibition of 5-Enolpyruvylshikimate-3-Phosphate Synthase (EPSPS)

Herbicides that inhibit 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) are among the most widely used, particularly those based on glyphosate. EPSPS is an enzyme in the shikimate pathway, essential for the synthesis of aromatic amino acids in plants. Inhibition of EPSPS prevents the production of these amino acids, leading to plant death. Glyphosate, a non-selective herbicide, is commonly used for weed control in glyphosate-tolerant crops.

5. Inhibition of Glutamine Synthetase

Glutamine synthetase inhibitors, such as glufosinate, are another class of herbicides. Glutamine synthetase is an enzyme involved in the synthesis of glutamine, an amino acid critical for plant growth. By inhibiting this enzyme, glufosinate leads to the accumulation of toxic levels of ammonia within plant cells, resulting in rapid cell death. This mode of action is effective against a wide range of weed species and is used in both agricultural and non-agricultural settings.

6. Inhibition of Mitosis

Herbicides that inhibit mitosis, such as dinitroanilines, exert their effect by disrupting microtubule formation in the mitotic spindle of plant cells. Microtubules are essential for cell division, and their disruption prevents normal cell division and elongation, leading to plant death. These herbicides are primarily used for pre-emergence control of grassy weeds in a variety of crops.

7. Inhibition of Cell Wall Synthesis

Herbicides that inhibit cell wall synthesis, such as isoxaben, act by preventing the formation of new cell walls, which is necessary for cell division and plant growth. This mode of action is primarily effective against broadleaf weeds and is used for pre-emergence weed control in certain crops.

8. Uncouplers of Photosynthesis

Uncouplers of photosynthesis, such as paraquat, act by disrupting the electron transport chain in photosynthesis. This disruption leads to the generation of toxic reactive oxygen species, which cause cellular damage and lead to plant death. These herbicides are non-selective and are used for burndown applications and in areas where non-selective weed control is needed.

9. Inhibition of Phytoene Desaturase (PDS)

Herbicides that inhibit phytoene desaturase (PDS) are used for controlling certain types of weeds. PDS is an enzyme involved in the biosynthesis of carotenoids, which are essential pigments for protecting the photosynthetic apparatus from excessive light energy. Inhibition of PDS leads to the accumulation of colorless carotenoid precursors and a reduction in carotenoid levels, resulting in plant bleaching and death.

10. Inhibition of Dihydropteroate Synthase (DHPS)

Herbicides that inhibit dihydropteroate synthase (DHPS) are part of a newer class of herbicides. DHPS is an enzyme involved in the synthesis of folate, which is essential for plant growth. Inhibition of DHPS prevents folate synthesis, leading to the inhibition of plant growth and eventual plant death. This mode of action offers another tool for weed management, particularly for weeds that have developed resistance to other herbicides.