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🪱 Parasitic and Aquatic Weeds: Types, Examples, Hosts and Control

Answer-first notes on parasitic weeds like Orobanche, Striga, Cuscuta and Loranthus, plus aquatic weeds like Eichhornia, Salvinia and Hydrilla for agriculture exams.

When Weeds Feed on Crops

Quick answer: Parasitic weeds attach to a host through haustoria and steal food, water or minerals; the four exam types are Orobanche (total root), Striga (partial root), Cuscuta (total stem) and Loranthus (partial stem). Aquatic weeds grow in water bodies; the most asked examples are Eichhornia crassipes (water hyacinth), Salvinia molesta, Hydrilla, Typha and lotus.

Parasitic weeds feeding on crop roots and stems through four attachment types — Parasitic weeds do not simply compete; they attach to crop roots or stems and draw resources directly from the host.

Search Query / Exam Prompt	Direct Answer
Parasitic weed of tobacco	Orobanche (broomrape), a total root parasite
Parasitic weed of sorghum / maize	Striga (witch weed), a partial root parasite
Parasitic weed of lucerne	Cuscuta (dodder), a total stem parasite
Parasitic weed of mango	Loranthus, a partial stem parasite
Worst floating aquatic weed in India	Eichhornia crassipes (water hyacinth)
World's worst aquatic weed	Salvinia molesta
Submerged aquatic weed example	Hydrilla

In the previous lesson, we explored the 12 classification systems of weeds, including a brief mention of parasitic and aquatic weeds under "specificity." Now we dive deep into these two special categories that behave very differently from ordinary weeds -- they do not merely compete, they directly parasitise host plants or infest water bodies.

In the tobacco fields of Andhra Pradesh, farmers sometimes notice stunted, yellowing plants long before any above-ground intruder is visible. Underground, Orobanche (broomrape) has already latched onto the tobacco roots, silently draining water and nutrients. By the time its fleshy purple flower stalk breaks through the soil, the damage is done.

This lesson covers:

Four types of parasitic weeds -- total/partial, root/stem combinations
Aquatic weed categories -- submerged, emerged, marginal, floating
Control methods for parasitic and aquatic weeds
Taxonomic families of important weeds

Parasitic Weeds -- Overview

Cuscuta dodder wrapped around host stems as a total stem parasitic weed — Cuscuta shows how a total stem parasite physically attaches to the host and draws nutrients through haustoria.

Parasitic weeds are classified on two axes:

Degree of dependence: Total (holoparasite -- no chlorophyll) vs Partial (hemiparasite -- develops chlorophyll later)
Site of attachment: Root parasite vs Stem parasite

This creates four distinct types:

Parasitic Weeds Exam Table

Type	Example	Common Name	Main Host / Crop	One-Line Identification	Control Pointer
Total root parasite	Orobanche	Broomrape	Tobacco, tomato, mustard, solanaceous crops	Fleshy, non-green shoot emerges near host	Long rotation; trap crop such as chilli
Partial root parasite	Striga	Witch weed	Sorghum, maize, sugarcane	Damage starts before emergence	Resistant varieties, rotation, sanitation
Total stem parasite	Cuscuta	Dodder	Lucerne, niger, linseed	Yellow/orange thread-like vine	Clean seed; 20% salt solution seed separation
Partial stem parasite	Loranthus	Birdvine	Mango and fruit trees	Green parasite on branches	Pruning / directed herbicide on infected branch

Type 1: Total Root Parasite (Holoparasite)

Takes all nutrition from host roots. Completely lacks chlorophyll -- appears as non-green, fleshy structures emerging from soil near the host.

Orobanche sp. (Broomrape) parasitises tobacco, tomato, fababean, chickpea, mustard, chilli, brinjal, potato -- mostly Solanaceous crops
Attaches to host roots underground; difficult to detect until it emerges to flower
Control: Long crop rotation with tobacco once in 3 years, preceded by chilli as a trap crop (stimulates Orobanche germination but chilli is a poor host, so the parasite dies without reproducing)

Type 2: Partial Root Parasite (Hemiparasite)

Depends on host roots during the underground stage, but after emergence becomes green and photosynthetic -- a "semi-independent" parasite.

Striga hermonthica / asiatica (= lutea) (Witch weed) attacks sorghum, maize, sugarcane, sunflower
Called "witch weed" because it causes severe crop damage before it even emerges -- the crop appears bewitched
Striga gesnerioides specifically parasitises cowpea

Type 3: Total Stem Parasite (Holoparasite)

Takes all nutrition from the host stem through specialised haustoria. No chlorophyll -- appears as yellow or orange thread-like vines wrapping around the host.

Cuscuta campestris / chinensis / epilinum (Dodder) parasitises alfalfa (lucerne), niger, linseed respectively
Earlier placed in family Convolvulaceae; now in separate family Cuscutaceae
Control: Float fenugreek and lucerne seeds in 20% salt solution before sowing -- lighter Cuscuta seeds float to the surface for easy removal

Type 4: Partial Stem Parasite (Hemiparasite)

Initially depends on host stem, but later becomes green and can photosynthesise. Typically attacks perennial woody plants.

Loranthus longiflorus (Birdvine) -- found on mango and other fruit trees; birds disperse its sticky seeds
Cassytha filiformis on orange, eucalyptus -- twines anti-clockwise like Cuscuta but is greener (partial photosynthesis)
Control: Spray of Glyphosate + 0.2% on infected branches

Comparison Table: Four Types of Parasitic Weeds

Feature	Total Root	Partial Root	Total Stem	Partial Stem
Example	Orobanche	Striga	Cuscuta	Loranthus
Common Name	Broomrape	Witch weed	Dodder	Birdvine
Chlorophyll	Absent	Develops after emergence	Absent	Develops later
Attachment	Host roots (underground)	Host roots (underground)	Host stem (above ground)	Host stem (above ground)
Host Crops	Tobacco, mustard, Solanaceae	Sorghum, maize, sugarcane	Lucerne, niger, linseed	Mango, fruit trees
Dependence	100% on host	Partial (semi-independent)	100% on host	Partial (semi-independent)

TIP

Mnemonic -- "CLOS": Cuscuta (Total Stem), Loranthus (Partial Stem), Orobanche (Total Root), Striga (Partial Root). This order covers all four types.

NOTE

The key distinction: Total parasites have NO chlorophyll (completely dependent), while Partial parasites develop chlorophyll after emergence (semi-independent).

Four parasitic weed types showing total root partial root total stem and partial stem attachment patterns — The four parasitic weed types are best understood by combining the attachment site with whether the parasite remains fully dependent or becomes green after emergence.

Aquatic Weeds

Water hyacinth floating densely on a water body as an aquatic weed — Floating aquatic weeds such as water hyacinth can blanket water surfaces and disrupt irrigation, fisheries, and drainage.

While parasitic weeds attack crops directly by feeding on them, aquatic weeds create a different set of problems entirely. They grow in water and complete at least part of their life cycle in water, choking waterways, impeding irrigation, reducing dissolved oxygen, and lowering fish production. Unlike terrestrial weeds that compete in fields, aquatic weeds disrupt water infrastructure critical for agriculture. They are classified by their position relative to the water surface.

ICAR's Indian Farming review lists water hyacinth, water fern, alligator weed and water lettuce among important floating aquatic weeds in India; lotus, cattail and water lily among emergent weeds; and Hydrilla, bladderwort and Eurasian water milfoil among submerged problem weeds. This is why exam questions usually ask both growth position and common example.

1. Submerged Weeds

Produce most vegetative growth beneath the water surface. Leaves are thin and finely divided to maximise surface area for absorbing dissolved gases.

Examples: Utricularia stellaris, Ceratophyllum demersum, Hydrilla

2. Emerged (Emersed) Weeds

Rooted in bottom mud, with aerial stems and leaves at or above the water surface. They do not rise or fall with changing water levels -- rigid stems hold them in place.

Examples: Nelumbium speciosum (Lotus), Jussiaea repens

3. Marginal Weeds

Emergent rooted weeds found in moist shoreline areas with water depth up to 0.5 metres (60-90 cm). They form dense stands along pond, lake and canal edges.

Examples: Typha sp. (Cattail), Polygonum sp., Cephalanthus, Scirpus

4. Floating Weeds

Leaves float on the water surface. Some are free-floating (not attached to the bottom), others are rooted with floating leaves. Free-floating types spread most rapidly.

Weed	Common Name	Key Fact
Eichhornia crassipes	Water Hyacinth	Known as "weed of fishermen"; provides fish breeding ground but clogs water bodies
Salvinia molesta	--	Considered the world's worst aquatic weed; can double biomass in days
Pistia stratiotes	Water cabbage	Free-floating rosette
Nymphaea sp.	Water lily	Rooted with floating leaves

Comparison of Aquatic Weed Types

Type	Position	Rooted?	Example
Submerged	Below water surface	Yes	Hydrilla, Ceratophyllum
Emerged	Stems above water, rooted in mud	Yes	Lotus, Jussiaea
Marginal	Shoreline, up to 0.5 m depth	Yes	Typha (Cattail)
Floating	On water surface	Some yes, some no	Eichhornia, Salvinia

IMPORTANT

For control of aquatic weeds, the two most commonly used chemicals are 2,4-D and Copper Sulphate (CuSO4).

Aquatic weed growth positions showing submerged emerged marginal and floating weeds in a pond — Aquatic weeds are classified by where they grow relative to the water surface, which helps explain why their control methods differ.

Obsolete Mechanical Controls for Aquatic Weeds

Method	How It Works
Chaining	Heavy chain pulled through ditch bottom by two tractors on either bank, uprooting submerged weeds
Dredging	Mechanical pulling of weeds along with roots and rhizomes embedded in bottom mud

Both methods are rarely used today due to high cost and environmental disturbance.

Families of Important Weeds

Beyond the parasitic/aquatic distinction, knowing the taxonomic family of a weed is essential because herbicide selectivity often works at the family level. A herbicide effective against Poaceae (grasses) may be useless against Cyperaceae (sedges) or Asteraceae (composites).

Important weed families shown as grasses sedges and broadleaf groups with Poaceae Cyperaceae and Asteraceae traits — Family-level weed identity supports herbicide decisions because grasses, sedges, and broadleaf weeds often respond differently.

Weed	Family
Lantana camara	Verbenaceae
Striga spp.	Scrophulariaceae
Argemone mexicana	Papaveraceae
Echinochloa spp.	Gramineae (Poaceae)
Cyperus rotundus	Cyperaceae
Parthenium hysterophorus	Asteraceae
Cuscuta spp.	Cuscutaceae (earlier Convolvulaceae)

TIP

The two most important weed families are Poaceae (grasses -- monocot weeds) and Asteraceae (composites -- dicot weeds like Parthenium).

Summary Cheat Sheet

Summary visual of parasitic and aquatic weed categories for weed science revision — The lesson summary connects two special weed groups: parasites classified by attachment site and aquatic weeds classified by growth position.

Concept / Topic	Key Details
Total root parasite	Orobanche (Broomrape) — no chlorophyll; attacks Solanaceae
Partial root parasite	Striga (Witch weed) — develops chlorophyll; attacks sorghum/maize
Total stem parasite	Cuscuta (Dodder) — no chlorophyll; attacks lucerne/niger
Partial stem parasite	Loranthus (Birdvine) — develops chlorophyll; attacks mango
Parasitic mnemonic	CLOS: Cuscuta, Loranthus, Orobanche, Striga
Cuscuta seed separation	Float in 20% salt solution
Cuscuta family	Cuscutaceae (not Convolvulaceae)
World's worst aquatic weed	Salvinia molesta
Weed of fishermen	Eichhornia crassipes (Water Hyacinth)
Aquatic weed chemicals	2,4-D and Copper Sulphate
Most important weed families	Poaceae (grasses) and Asteraceae (Parthenium)
Parthenium family	Asteraceae
Cyperus rotundus family	Cyperaceae
Lantana camara family	Verbenaceae
Marginal weeds depth	Up to 0.5 metres
Orobanche control	Crop rotation; chilli as trap crop
Loranthus control	Spray Glyphosate + 0.2% on infected branches
Striga on cowpea	Striga gesnerioides specifically parasitises cowpea