Questions and Answers
What is the purpose of classifying 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.
False
What is the difference between contact and systemic herbicides?
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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.
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Name any two types of 'Mode-of-action' for herbicides.
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How do systemic herbicides translocate?
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Chemicals with the same core molecule belong to the same ________.
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What is 'persistence' in terms of herbicides?
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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.