Lesson 2.2 Weed Characteristics, Identification, and Classification

Characteristics of Weeds

1. Rapid seedling growth and ability to produce when

young

2. Quick maturation or short vegetative growth

3. Ability to germinate and grow in many environments

4. Self-compatibility or easy cross-pollination

5. Longevity of seeds

6. Long period of seed production

7. High seed output

8. Long- and short-range seed dispersal

mechanism

9. Have great competitive ability for nutrient,

light, and water

10. Dual reproduction: by seeds and may reproduce vegetatively

11. Ability to tolerate environmental stresses and cultivation

How many plant species of weeds exist worldwide?

250,000

How many weeds are crop cultivated?

200

Ratio in which weeds cause major problem in any one crop

25:1

Weed Classification Based on Gross Morphology

• Grasses

• Sedges

• Broadleaves

Botanical Family of Grass Weeds

Poaceae or Graminae family

Cotyledon classification of grass weeds

Monocot

Leaf shape and venation pattern of grass weeds

Narrow leaves with parallel venation

Leaf arrangement along the stem in grass weeds

Alternate arrangement

Name and structure of the main grass weed stem that is typically round and hollow

Culm

Structural divisions of a grass stem (culm)

Nodes and internodes

Distinctive vegetative appendage options at the leaf collar region in grasses

Auricles and/or ligules

Botanical family of sedges

Cyperaceae

Cotyledon classification of sedges

Monocot

Stem cross-section shape and internal structure of sedges

Triangular and solid

Leaf shape and venation pattern of sedges

Leaf shape and venation pattern of sedges

Leaf sheath arrangement in sedges that forms a tube and gives rise to a rosette arrangement

Fused leaf sheaths

Key vegetative structures absent in sedges

Nodes and Ligules

Botanical family classification of broadleaf weeds

Belongs to plant families other than Poaceae and Cyperaceae

Cotyledon classification of broadleaf weeds

Majority are dicots; few monocots

Venation pattern of broadleaf weed leaves

Netted venation

Leaf arrangement in broadleaf weeds

Arranged in various manners

Branching structure of broadleaf weed stems

• primary

• secondary

• tertiary

Weed Classification Based on Life Span

• Annual

• Biennial

• Perennial

Annual

Complete their life cycle from seed to seed in less than 12 months

Biennial

Plants that take two years to complete their life cycle before producing seeds and dying

Perennial

Complete their life cycle from seed to seed more than a year or two

Weed Classification Based on Association with Man

• Obligate weeds

• Facultative weeds

Obligate weeds

Weeds associated whenever crops are grown

Facultative weeds

Those that are present in cultivated fields as well as wild state

Weed Classification Based on Soil pH

• Acidophile

• Basophile

• Neutrophile

Acidophile

Acid soil weeds

Basophile

Saline and alkaline soil weeds

Neutrophile

Weeds of neutral soils

Other Weeds Classification

6. Weeds

7. Body Texture

8. Origin

9. Number of Cotyledons

Weed Classification Based on Habitat

• Terrestrial

• Aquatic

• Epiphytic

Weed Classification Based on Body Texture

• Herbaceous

• Woody

Weed Classification Based on Origin

Native/Indigenous

•Exotic/Introduced

Weed Classification Based on Number of Cotyledons

Monocot

Dicot