Agronomy: Science of Crop Production

• Agronomy is the science and technology of producing and using plants for food, fuel, feed, fiber, and reclamation.
• Agronomy encompasses work in the areas of plant genetics, plant physiology, meteorology, and soil science.
• Agronomy is the application of a combination of sciences.

Agronomic practices

• Crop rotation is the practice of planting different crops sequentially on the same plot of land, improving soil health, optimizing nutrients, and combating pest/weed pressure.
• Tillage prepares land for growing crops by disturbing the soil through digging, stirring, and overturning.
• Irrigation is the artificial application of water to soil, assisting in crop production.
• Fertilization adds nutrients to the soil to improve crop production.
• Pest and weed control protects crops from damage.

Weeds

• Weeds are unwanted plants.
• Weeds vie with crops for sunlight, water, and nutrients.
• Weeds diminish both crop yields and quality.
• Weeds can be problematic in agricultural, residential, and recreational areas.
• Weeds interfere with harvesting and harbor pests/diseases.

Weed Characteristics

• High seed production: Many weed species generate numerous seeds per plant.
• Seed dormancy: Allows seeds to persist in the soil for long periods, germinating when conditions are right.
• Rapid growth and development: Enables weeds to quickly establish and compete with crops.
• Vegetative reproduction: Allows weeds to spread via rhizomes, stolons, or other vegetative structures.
• Adaptability: Weeds thrive in diverse soil types, climates, and conditions.
• Allelopathy: Weeds produce biochemicals influencing the growth/survival of other plants, including crops.

Weed Classification

• Broadleaf weeds feature two cotyledons, net-like veins, and broad leaves, such as dandelions, thistles, and clover.
• Grass weeds have one cotyledon, narrow upright leaves, and parallel veins, including crabgrass, foxtail, and quackgrass.
• Sedges resemble grasses but have triangular stems and typically grow in wet areas; examples include nutsedge and bulrush.
• Annual weeds complete their life cycle in one year, germinating, growing, reproducing, and dying in a single season.
• Biennial weeds live for two years, growing vegetatively in the first and reproducing in the second.
• Perennial weeds live longer than two years and reproduce by seed or vegetatively.

Weed Control Methods

• Prevention is the optimal approach.
• Cultural control uses agronomic practices to suppress weeds.
• Mechanical control involves physically removing weeds.
• Chemical control uses herbicides.
• Biological control uses natural enemies.
• Integrated Weed Management (IWM) combines methods.

Preventative Weed Control

• Utilize clean, weed-free seeds.
• Clean equipment to prevent weed spread.
• Control weeds in non-crop areas.
• Regularly monitor fields for infestations.
• Quarantine new plant materials to avoid introducing new weed species.

Cultural Weed Control

• Crop rotation suppresses weeds by altering the environment and disrupting lifecycles.
• Cover crops compete with and suppress weeds.
• Planting date impacts weed emergence and competition.
• Plant density affects weed competition.
• Irrigation management influences weed growth and herbicide effectiveness.
• Fertilization management impacts weed competition.
• Soil health influences weed growth and crop competitiveness.

Mechanical Weed Control

• Tillage kills existing weeds and prepares the seedbed.
• Cultivation controls weeds between crop rows.
• Hand weeding removes weeds from small areas.
• Mowing manages weeds in non-crop areas.
• Burning controls weeds in specific situations.

Chemical Weed Control

• Herbicides are chemicals that kill weeds.
• Selective herbicides kill certain weeds without harming the crop.
• Non-selective herbicides kill all vegetation.
• Pre-emergence herbicides are applied before weed emergence.
• Post-emergence herbicides are applied after weed emergence.
• Systemic herbicides are absorbed and translocated throughout the plant.
• Contact herbicides kill only the contacted parts of the plant.

Biological Weed Control

• Natural enemies include insects, fungi, and bacteria.
• Biological control agents suppress weed populations.
• Grazing animals can control weeds in some cases.

Integrated Weed Management (IWM)

• IWM is a comprehensive approach.
• Prevention is foundational.
• Cultural and mechanical controls suppress weeds.
• Herbicides are used judiciously.
• Biological control supplements other methods.
• Monitoring evaluates IWM effectiveness.

Herbicide Resistance

• Herbicide resistance enables weeds to survive normally lethal herbicide applications.
• Resistance develops with repeated herbicide use.
• Resistance complicates and increases the cost of weed control.
• Rotating herbicides with different modes of action prevents resistance.
• IWM reduces herbicide reliance and delays resistance development.

Herbicide Mode of Action

• Amino Acid Synthesis Inhibitors: Disrupt protein synthesis and plant growth by inhibiting essential amino acid production; examples include glyphosate and sulfonylureas.
• Cell Growth Inhibitors: Interfere with cell division, causing abnormal development; examples include dinitroanilines.
• Photosynthesis Inhibitors: Block photosynthesis, preventing energy production; examples include triazines.
• Lipid Synthesis Inhibitors: Inhibit lipid production, essential for cell membranes; examples include clethodim.
• Growth Regulators: Mimic plant hormones, causing abnormal growth; example: 2,4-D.

Weed Management Planning

• Identify weed species in the field.
• Assess weed density and distribution.
• Consider the crop and its susceptibility to competition.
• Select appropriate control methods based on weed species, crop, and conditions.
• Develop an integrated weed management plan.
• Implement the plan.
• Monitor effectiveness and adjust as needed.

Agronomy is the science and technology of producing and using plants for various purposes. It combines plant genetics, physiology, meteorology, and soil science. Agronomic practices include crop rotation, tillage, irrigation, fertilization, and pest control used to enhance crop production.