AGRIC SCIENCE THIRD TERM JSS1 LESSON PLAN/SCHEME OF WORK
DEFINITION AND CHARACTERISTICS OF WEEDS
- 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
|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|
|13.||Kuzu or puero||Pueraria phaseoloides|
|15.||Sun hemp||Crotolaria juncea|
|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.
- Define weeds
- Name 10 common weeds and their botanical names
- State 5 characteristics of weeds
CLASSIFICATION OF WEEDS
- 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.
(c) Epiphytic/parasitic weeds: These are weeds that grow on other plants.
|S/n||Epiphytic/parasitic weeds||Crop attacked|
|2.||Dodder||Cassava and pumpkin|
|3.||Mistletoe||Kola and cocoa|
- 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.
- 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
- 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.
- 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.
- Chemical weed control: This involves the use of chemicals to control weeds.
The chemical used to control weeds are called herbicides. The machine used to apply herbicides is called a sprayer.