AGRI 103: Agronomy - Crop Management

AGRI 103: Agronomy - Crop Management

Agricultural Weeds

• Definition: Agricultural weeds are plants that are considered undesirable and interfere with the growth of crops.

Effects of Weeds on Crop Growth

• Reduce the yield of crops by competing for essential growth resources, which include:

  • Light: Weeds effectively compete for light and can hinder crop growth.

  • Water: Weeds absorb water from the soil, affecting moisture available to crops.

  • Nutrients: Weeds can absorb nutrients, resulting in nutrient deficiencies in crops.

• Weeds develop advanced growth rates, allowing them to grow taller and develop larger leaf areas more quickly than the crops, which can lead to:

  • A reduction in the intensity and quality of light that the crop receives.

  • Belowground competition for water and nutrients, where greater rooting volumes and depths provide advantage to weeds.

Allelopathic Weeds

• Some weeds exhibit allelopathy, which is:

  • The adverse effect of one plant on another due to the production of a chemical inhibitor.

  • These chemicals may be excreted by living or decaying plant tissue.

  • Allelopathy can lead to:

  • Reduced seed germination.

  • Impaired seedling growth.

  • While allelopathic interactions are present, they are relatively minor compared to direct competition for resources.

• Examples: Canada thistle, quackgrass, and wild oats are known for their allelopathic effects.

Crop Diseases

• Definition: Plant diseases have detrimental effects on various aspects of plant development, appearance, or function.

• Disease Incidence Criteria: Three factors must be present for plant disease to occur:

  • Pathogen: A disease-causing agent (e.g., fungi, bacteria, viruses)

  • Susceptible Host: The susceptible crop that cannot resist infection.

  • Favourable Environment: Conditions that allow the pathogen to infect and develop.

• This concept is often represented using the Disease Triangle.

Insect Pests

• Impact on Crops:

  • Direct damage occurs as pests consume crops, leading to:

  • Reduced leaf area by methods such as defoliation, leaf mining, and leaf curling.

  • Suckling sap, which decreases the amount of photosynthate available for plant growth and grain yield.

  • Boring into stems contributes to lodging.

  • Chewing insects may damage grains before harvest.

  • Root-feeding insects can injure or kill plants by compromising their root systems.

• Plant Pathogen Vectors: Insect pests may act as vectors for plant pathogens.

Beneficial Insects

• Beneficial insects include:

  • Pollinators that aid in plant reproduction.

  • Predators of crop insect pests that help maintain pest populations at manageable levels.

Adaptation of Weeds, Diseases, and Insect Pests

• Many weeds, diseases, and insect pests adapt in response to control efforts, through mechanisms such as:

  • High seed production.

  • Seed dormancy and effective seed dispersal mechanisms.

  • Vegetative reproduction.

• Limitations of Single Management Approaches: Sole reliance on a single management approach, such as pesticides, may not be effective alone and could reduce the effectiveness over time.

• Sustainable Pest Control: The most sustainable strategies involve a combination of different methods.

Integrated Pest Management (IPM)

• IPM Steps:

  • Accurate Pest Identification: Correctly identify the pest for effective management.

  • Life Cycle Examination: Understand the life cycle of the pest and its interaction with the host crop and environment.

  • Method Identification: Identify the most effective method or combination of methods for pest control.

  • Non-target Impacts Consideration: Evaluate potential impacts on non-target species when applying control methods.

Methods of Pest Management

1. Genetic Methods

   • Plant Breeding: This involves developing crop varieties that are more resistant to important plant pests.

   • Variety Development in Saskatchewan: Varieties undergo testing to ensure efficacy.

   • Pest Adaptation: Overuse of the same crop traits may allow pests to adapt and overcome resistance over time.

2. Cultural Methods

   • Irrigation and Fertilization: Proper methods support optimal plant growth and development.

   • Well-hydrated crops with robust nutrient profiles can outcompete weeds and resist pests and diseases.

   • Crop Configuration: Involves plant density and row spacing considerations:

     • Higher densities can help in weed competition but may also create microclimatic conditions conducive to pests.

   • Sanitation Practices: These include:

     • Removing or incorporating crop residues to destroy disease pathogens and insects.

     • Cleaning or sterilizing equipment to prevent contamination of new areas.

     • Using disease-free seeds to prevent the introduction of pathogens.

   • Crop Rotation: A sequence of different crops grown on the same land over the years that:

     • Varies in length and diversity to disrupt the life cycles of pests.

     • Helps with disease and insect control by removing their hosts.

     • Aids in weed control by reducing the selection for weeds adapted to specific cropping systems.

     • Rotations should include crops from different plant families, such as grasses versus broadleaf species.

3. Biological Methods

   • Utilizes natural predators, parasites, or competitors to reduce or eliminate target pests:

     • Positive impacts on the pest populations should not affect non-target species.

     • Effects may take several seasons as control agents work to weaken pests and prevent reproduction.

     • Some biological methods are dependent on specific climatic conditions for effectiveness.

     • Beneficial Practices: Encourage populations of beneficial insects without harming them through other management practices.

     • Natural plant chemicals and toxins may be applied like pesticides for added efficacy.

4. Mechanical/Physical Methods

   • Tillage: Breaks up plant residue and incorporates them into the soil where soil organisms may degrade pathogens or insects:

     • May control weeds by burying seeds or seedlings and uprooting mature plants.

     • Should be timely to target weeds at specific growth stages:

     • Very effective against small seedlings, less effective against perennials or annuals with large root systems.

     • Drawbacks:

     • Can lead to soil structure degradation and increased erosion.

     • Can stimulate germination of dormant seeds while promoting some asexual reproduction in species by cutting and moving them.

   • Mowing: Effective in removing aboveground portions of plants and may:

     • Kill many annuals with limited roots, but perennials may not die and can regenerate from basal buds.

     • Repeated mowing can weaken perennials but may not destroy them completely.

5. Chemical Methods

   • Pesticides: Effective but must be used judiciously to:

     • Preserve effectiveness by preventing pest resistance.

     • Avoid damage to crops through direct and residual effects.

     • Prevent environmental hazards like soil and water contamination and harm to beneficial organisms.

   • Chemical Treatments: Can be applied in various forms:

     • Seed Treatments: To protect seeds before germination.

     • Soil and Foliar Treatments: Direct application to plants or soil.

     • Fumigants: Used to treat soil or storage facilities for pests.

   • Proper pest identification and understanding of pest life cycles are crucial for determining the correct chemical and dosage applicable when pests are most vulnerable.

Advantages of Herbicides

• Herbicides provide:

  • Greater flexibility in timing for weed control compared to mechanical methods.

  • Ability to selectively target specific weed species without harming crops, depending on their mode of action and crop tolerance.

  • Potential to eliminate the need for tillage.

  • Some herbicides can persist in soil, offering long-term weed control.