📈 Weed Classification and Identification

This lesson builds core elective concepts in BSc Agriculture with practical applications and exam-oriented clarity.

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Weed Classification and Identification

Accurate identification and classification of weeds is the first step in developing effective weed management programmes. Weeds are broadly categorised by their morphological features into grasses, broadleaves, sedges, and parasitic weeds.

Quick Field ID Rules

If you observe...	Most likely group
Narrow leaves + parallel venation + hollow culm	Grass
Broad leaves + reticulate venation + tap root	Broadleaf
Triangular solid stem + three-ranked leaves	Sedge
Direct attachment on host stem/root	Parasitic weed

Grasses (Family Poaceae)

Grasses are monocotyledonous weeds characterised by:

• Narrow, linear leaves with parallel venation
• Hollow, cylindrical stems (culms) with distinct nodes
• Fibrous root system
• Flowers arranged in spikelets

Important Grass Weeds in India

Weed	Common Name	Crops Affected
Phalaris minor	Little seed canary grass	Wheat
Echinochloa crusgalli	Barnyard grass	Rice
Cynodon dactylon	Bermuda grass	All crops (perennial)
Avena fatua	Wild oat	Wheat, barley
Digitaria sanguinalis	Crab grass	Maize, vegetables

Broadleaf Weeds (Dicots)

Broadleaf weeds have net-veined leaves, tap root systems, and flowers with distinct petals:

• Chenopodium album (bathua) — major rabi season weed
• Parthenium hysterophorus (congress grass) — invasive weed in wastelands and crops
• Convolvulus arvensis (field bindweed) — perennial twining weed
• Amaranthus viridis (pigweed) — common in kharif crops
• Trianthema portulacastrum (horse purslane) — problematic in cotton, groundnut

Sedges (Family Cyperaceae)

Sedges are often confused with grasses but differ in key features:

• Triangular stems (the mnemonic: "sedges have edges")
• Leaves arranged in three ranks
• Solid stems (unlike hollow grass culms)
• Cyperus rotundus (purple nutsedge) is ranked the world's worst weed
• Cyperus iria and Fimbristylis miliacea are common in rice paddies

Parasitic Weeds

Parasitic weeds derive nutrition partially or fully from host plants:

• Holoparasites (total parasites) — Cuscuta (dodder) on lucerne, linseed; lacks chlorophyll entirely
• Hemiparasites (partial parasites) — Striga (witchweed) on sorghum, maize; has some photosynthetic ability
• Root parasites — Orobanche (broomrape) on mustard, tobacco; attaches to host roots underground
• Parasitic weeds cause severe yield losses (up to 100% in Striga-infested sorghum fields)

Correct identification — whether grass, broadleaf, sedge, or parasite — directly determines the choice of herbicide and management approach.

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Summary Cheat Sheet

Topic	Key takeaway
Main focus	Weed Classification and Identification — grasses, broadleaves, sedges, and parasitic weeds with key identification features.
Section context	Revise this lesson with the rest of Weed Management for stronger conceptual continuity.