Questions and Answers
What is one way in which weeds damage agricultural plants?
Competing with crops for essential nutrients
How do weeds affect the process of photosynthesis in crop plants?
By shading crop plants and reducing available sunlight
What is a potential consequence of weeds harboring insects and disease organisms?
Spreading pests and diseases to the crops
How do weed seeds impact the value of soybeans?
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Which method is used to control weeds by targeting specific weed species without affecting crop plants?
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What is a challenge associated with controlling weeds among crop plants?
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What is one disadvantage of picking cotton among weeds?
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Why was the use of mechanical means for battling weeds considered expensive?
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What is the purpose of selective herbicides?
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What distinguishes nonselective herbicides from selective herbicides?
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Why are chemical herbicides preferred over mechanical means for controlling weeds?
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What challenge is posed by the wide variety of weeds that infect crops?
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What is a benefit of Bt-mediated insect resistance compared to spraying pesticides?
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What is a major problem faced by producers using chemical pesticides to control insects that attack plant roots?
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Why can spraying pesticides over thick foliage be problematic?
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What is a challenge associated with systemic pesticides in food crops?
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What is one problem with plants treated with systemic pesticides?
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Why can topical application of chemicals be ineffective if an insect has burrowed into the stem of a plant?
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Study Notes
Weeds in Agriculture
- Cotton picked with weeds has reduced profit due to the need to remove trash from the lint
- Mechanical means of controlling weeds, such as hoeing and plowing, are expensive and can lead to soil erosion
- Chemical herbicides were developed to kill weeds, with non-selective herbicides killing all plants and selective herbicides killing specific types of plants
Types of Herbicides
- Non-selective herbicides, also known as knockdown herbicides, kill all plants they are applied to
- Selective herbicides kill certain types of plants, such as grasses or broadleaf plants
Problems with Herbicides
- Application of pesticides can be expensive due to machinery, fuel, and labor costs
- There is a wide variety of weeds that infect crops, making it difficult to control them
- Selective herbicides may not be effective against all types of weeds
Effects of Weeds on Agriculture
- Weeds compete with crops for essential growth materials, such as soil nutrients
- Weeds can shade crops, reducing sunlight and slowing crop growth
- Weeds can harbor insects and disease organisms that can spread to crops
- Weeds can cause impurities in agricultural products, reducing their value
Benefits of Biotech Crops
- Biotech crops can provide a financial benefit to producers by reducing the need for pesticides
- Bt-mediated insect resistance protects all plant parts, unlike chemical pesticides which may not reach all areas of the plant
Limitations of Chemical Pesticides
- Chemical pesticides may not reach all areas of the plant, such as the roots or stems
- Systemic pesticides can be problematic due to the potential for residues in edible plant parts and the need for long withdrawal periods before harvest.
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