AGRIC SCIENCE THIRD TERM JSS1 LESSON PLAN/SCHEME OF WORK

DEFINITION AND CHARACTERISTICS OF WEEDS

CONTENT

Definition of Weeds
Some Common Weeds
Characteristics of Weeds

Definition of Weeds

Weeds are plants growing where they are not wanted or cultivated. A plant may be weed in one farm but crop in another farm. For instance, a cowpea plant growing in a cassava plot is a weed.

Some Common Weeds

Sida acuta


S/N	Names of Common Weeds	Botanical Names
1.	Guinea grass	Panicum maximum
2.	Bahama grass	Cynodon dactylon
3.	Carpet grass	Axonopus compressus
4.	Elephant grass	Pennisetum purpureum
5.	Spear grass	Imperata cylindrical
6.	Giant star grass	Cynodon plactostachyum
7.	Northern gamba	Andropogon gayanus
8.	Stubborn grass	Eleusine indica
9.	Southern gamba	Andropogon tectorum
10.	Aspilia Africana	African marigold
11.	Centro	Centrosema pubescens
12.	Calopo	Calopogonium mucunoides
13.	Kuzu or puero	Pueraria phaseoloides
14.	Stylo	Stylosanthes gracilis
15.	Sun hemp	Crotolaria juncea
16.	Mucuna	Mucuna utilis
17.	Goat weed	Ageratum conyzoides
18.	Stubborn weed	Arctium minus
19.	Sensitive plant	Mimosa pudica
20.	Blue feather	Commelina nudiflora
21.	Pig weed	Amaranthus spp
22.	Bush green	Amaranthus spinosus
23.	Water leaf	Talinum triangulare
24.	Sedge plant	Cyperus rotundus
25.	Tridax, PWD weed	Tridax procumbens

Characteristics of Weeds

Weeds have the following characteristics:

Weeds produce many seeds.
They can survive in adverse soil condition.
They grow very fast.
They have the ability to survive adverse soil and climatic conditions.
The seeds can remain dormant in the soil for a long time.
They are easily dispersed e.g by wind, animals, etc.
Seeds of weeds are highly viable.
They are resistant to trampling.
They produce large quantities of pollen grains/high reproductive capacity.
Most weeds are wind-pollinated.

EVALUATION

Define weeds
Name 10 common weeds and their botanical names
State 5 characteristics of weeds

CLASSIFICATION OF WEEDS

CONTENT

Classification of Weeds based on Habitat
Classification of Weeds based on Life Cycle
Classification of Weeds based on the Shape of the Leaves

Classification of Weeds based on Habitat

According to habitat, weeds are classified into the following three groups:

(a) Aquatic weeds: These are weeds that grow on water. Examples are water hyacinth, water lettuce, water lily etc.

(b) Terrestrial weeds: These are weeds that grow on land. Most weeds are terrestrial weeds. Examples are goat weeds, siam weeds, carpet grass, tridax, aspilia, elephant grass, water leaf, etc.


S/n	Epiphytic/parasitic weeds	Crop attacked
1.	Striga	Cereals
2.	Dodder	Cassava and pumpkin
3.	Mistletoe	Kola and cocoa

EVALUATION

Classify the following weeds in the table below; water lettuce, water leaf, tridax, dodder, water hyacinth, mistletoe.


Terrestrial weeds	Aquatic weeds	Epiphytic weeds

Classification of Weeds based on Life Cycle

According to life cycle, weeds are classified into the following three groups:

Annual weeds: These are weeds that complete their life cycle within one year. Examples are goat weed, Tridax, Emilia weed, pig weed, Aspilia, milk weed, Amaranthus spp, water leaf, etc.
Biennial weeds: These are weeds that complete their life cycle in two years. Examples are morning glory, wild carrot, etc.
Perennial weeds: These are weeds that complete their life cycle in more than two years. Examples are elephant grass, broom weed, spear grass, bahama grass, Kudzu, siam weed, carpet grass etc.

Classification of Weeds based on the Shape of the Leaves

According to the shape of the leaves, weeds are classified into the following two groups:

Broad-leaved (dicotyledonous weeds): These are weeds that have short and broad leaves with net venation and taproot system. Examples are centro, stubborn weed, goat weed, water leaf, calapo, mucuna, etc.
Grasses and Sedges (monocotyledonous weed): These are weeds that have long and narrow leaves with parallel venation and fibrous root system e.g. gamba grass, carpet grass, maize, elephant grass, guinea grass, etc.

EVALUATION

Mention two examples of the following: (i) Perennial weeds (ii) Annual weeds (iii) Biennial weeds
Explain the following with three examples each: (i) Monocotyledonous weeds (ii) Dicotyledonous weeds

USES OF WEEDS; METHODS OF WEED CONTROL

CONTENT

Uses of Weeds
Methods of Weeds Control

Uses of Weeds

Weeds are used for the following purposes:

Some weeds are used as cover crops.
Weeds are used as forage grasses and legumes for feeding animals e.g. elephant grass.
Weeds are used to prepare compost and green manure e.g. mucuna, pueraria.
They are used to control soil erosion e.g. bahama grass.
They serve medicinal purposes e.g. lemon grass.
Weeds are used as fuel (firewood) for cooking.
Weeds are used as flowers to beautify our environment e.g. morning glory.
They are used to purify the environment by removing carbon dioxide from the atmosphere.
Some weeds are edible e.g. water leaf.

EVALUATION

State five uses of weeds.

Methods of Weed Control

Weed control refers to any deliberate effort made by man to eliminate weed seeds or stop weed growth.

Weeds can be controlled by using following methods:

Physical/mechanical weed control
Chemical weed control
Cultural weed control
Biological weed control

Physical/mechanical weed control. It may be in the following forms:

(i) Hand pulling: The use of hand to remove weeds. It is most effective in the control of annual and biennial weeds of row crops

(ii) Hoeing: It entails using hoes to remove weeds.

(iii) Mowing: The use of mower to clear weeds.

(iv) Slashing: This is the use of cutlass to cut the weeds. In this method, only the shoot is destroyed, the roots are left intact in the soil. These may sprout again.

(v) Tillage: (ploughing and harrowing)

Other methods include flooding, smothering, heat treatment, etc.