Life Cycles & Weed Classification Flashcards

Weed Classification Methods

• Classification of weeds can be based on five methods: origin, habitat, taxonomy/morphology, life cycle, and physiology.

Origin of Weeds

• Weeds can be categorized as native (indigenous/apophytes) or alien (exotic/neophytes).
• Examples of alien invasive species in Canada include giant hogweed, Japanese knotweed, and leafy spurge.

Habitat Classification

• Weeds can be classified based on their habitat:
  • Agrestal
  • Ruderals
  • Grassland weeds
  • Aquatic weeds
  • Forest weeds
  • Environmental weeds

Taxonomy in Weed Classification

• Taxonomy involves naming species based on morphological features, particularly reproductive structures.
• Taxonomic classification groups plants with similar traits together.
• Many weeds belong to the Poaceae (grass) and Asteraceae (composite) families.
• Dicots are seedlings that produce two cotyledons, while monocots produce one.

Life Cycles of Weeds

• Weeds have three life cycle types: annuals, biennials, and perennials.
• Annual weeds complete their life cycle from seed to seed in less than one year, characterized by shallow roots and weak stems, and produce a large number of seeds.
• Types of annual weeds include summer annuals (germinate in spring, grow in summer, die before winter) and winter annuals (germinate in fall, grow in spring, die in summer).

Biennial Weeds

• Biennial weeds live longer than one year but less than two; they develop vegetatively in the first year and flower in the second year after a cold period.
• They typically have roots as storage organs after the first year, and examples include common burdock, biennial wormwood, henbit, and common groundsel.

Perennial Weeds

• Perennials live longer than two years and can reproduce multiple times (polycarpic).
• Simple perennials generally reproduce by seed (e.g., foxtail barley, dandelion), while creeping perennials reproduce by seed and vegetative organs.
• Forms of vegetative reproduction include:
  • Rhizomes: Underground stems (example: Johnson Grass).
  • Stolons: Horizontal creeping stems above ground (example: Bermuda grass).
  • Roots: Enlarged root systems with buds (example: field bindweed).
  • Tubers: Modified rhizomes for food storage (example: Nutsedge).
  • Bulbs: Modified stems that reproduce mainly through bulbs (example: Allium species).
  • Corms: Modified shoots with fleshy stems (example: Timothy).
• Woody perennials are not common in arable lands.

Physiological Aspects of Weeds

• Physiological classification is based on photosynthesis, especially the conversion of light energy into chemical energy.
• C4 plants have a more efficient photosynthetic process than C3 plants, which are more common and include wild oat, lambsquarters, and dandelion.
• C4 plants thrive better in warm, dry conditions (e.g., redroot pigweed, kochia, green foxtail).

Weed Management Practices

• Alien Invasive Weeds: Management involves containing the spread and employing biological control strategies.
• Native Weeds: Focus on containment is less critical; strategies may involve herbicide use or mechanical weeding.
• Habitat management practices include mowing, spraying, grazing, and predation.
• Herbicide selection should depend on whether the weeds are monocots (grasses) or dicots (broadleaf plants).
• Timing of weed control for perennials is best in the fall, as perennials relocate reserves to their roots during this time, enhancing herbicide efficacy.

C3 vs. C4 Weed Control

• Under poor growing conditions, C4 weeds are more competitive with C3 crops.
• In changing climate conditions, C3 weeds can become more competitive with increasing CO2 levels.