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Questions and Answers
What is the purpose of classifying herbicides?
What is the purpose of classifying herbicides?
What does 'selectivity' refer to in herbicides?
What does 'selectivity' refer to in herbicides?
The ability of a herbicide to kill certain plants without injury to others.
Non-selective herbicides kill only specific types of plants.
Non-selective herbicides kill only specific types of plants.
False
What is the difference between contact and systemic herbicides?
What is the difference between contact and systemic herbicides?
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Herbicides that enter the symplast move ________ and ________.
Herbicides that enter the symplast move ________ and ________.
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The half-life of a herbicide is used to predict its ________ in the soil.
The half-life of a herbicide is used to predict its ________ in the soil.
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Name any two types of 'Mode-of-action' for herbicides.
Name any two types of 'Mode-of-action' for herbicides.
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How do systemic herbicides translocate?
How do systemic herbicides translocate?
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Chemicals with the same core molecule belong to the same ________.
Chemicals with the same core molecule belong to the same ________.
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What is 'persistence' in terms of herbicides?
What is 'persistence' in terms of herbicides?
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What can cause variance within a chemical family of herbicides?
What can cause variance within a chemical family of herbicides?
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Study Notes
Herbicide Classification
- Classification categorizes herbicides to understand their uses and the weeds they control.
- Herbicides are classified by their application method, control targets, and chemical characteristics.
Application Timing
- Preplant: Applied to soil before seeding or transplanting.
- Preemergence: Herbicide is applied prior to the emergence of crops or weeds, generally after planting.
- Postemergence: Applied after crops or specific weeds appear; can be categorized into early, late, or directed treatments.
Selectivity in Herbicides
- Selectivity: The ability of a herbicide to kill specific plants while leaving others unharmed.
- Non-selective: Culls all plant types at recommended rates, typically used for total vegetation control.
Methods of Selectivity
- Physical Methods: Utilizes carbon seeding; herbicide application protects germinating crop seeds from herbicide while unprotected weeds germinate.
Types of Herbicides
- Contact Herbicide: Target localized areas and do not move through the plant; effective on annual plants; requires good coverage (e.g., Gramoxone).
- Systemic Herbicides: Move within the plant's transport system; effective against perennial weeds and can be applied to foliage or soil (e.g., Roundup).
Movement Characteristics
- Symplast Movement: Herbicides that enter the symplast move both upward (acropetally) and downward (basipetally).
- Apoplast Movement: Herbicides that enter the apoplast primarily move upward (acropetally).
Persistence and Degradation
- Persistence: Measured by half-life, indicates the longevity of herbicide efficacy in the soil; moderate persistence typically has a half-life of around 45 days.
- Half-Life: Time taken for 50% of the herbicide to degrade, a crucial factor in understanding herbicide behavior.
Chemical Families
- Chemical Family: Group of herbicides with similar core structures that often act in similar biochemical ways.
- Family Variance: Selectivity and persistence can significantly vary within a chemical family due to small structural changes.
Mode of Action
- Describes the sequence of biological events leading to plant death after herbicide application, explaining the herbicide's effects on susceptible plants.
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Eight General Modes of Action:
- Inhibition of lipid synthesis
- Inhibition of amino acid synthesis
- Growth inhibitors
- Inhibitors of photosynthesis
- Pigment inhibitors
- Cell membrane disrupters
- Seedling growth inhibitors
- Undefined or unknown mechanisms
Site of Action
- Site-of-Action or Group #: The most precise classification method for herbicides based on the specific biochemical pathway targeted in a plant; there are 20 distinct sites of action.
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Description
Explore the essential concepts of herbicide classification with these informative flashcards. Learn about the different types of herbicides, their applications, and the specific weeds they target. This tool offers a concise way to understand herbicide usage and timing for effective weed control.
