Subject :Agricultural science
DISPERSAL OF WEEDS (WEED DISSEMINATION)
Basic 7 / JSS 1
Instructional Materials :
- pictures of weeds
- samples of weeds
- Scheme of Work
- Online Information
- 9 Year Basic Education Curriculum
Previous Knowledge :
The pupils have previous knowledge of
Behavioural Objectives : At the end of the lesson, the pupils should be able to
- say the meaning of dissemination
- list methods of weed dissemination
- write out the advantages of weed dissemination
- say the disadvantages of weed dissemination
- Meaning of Weed Dispersal
- Agents of Weed Dispersal
Weeds are widely dispersed through various adaptations. This is one of the reasons why weeds survive and are found in almost all cultivated fields.
Meaning of Weed Dispersal
This is the process by which seeds of weeds, fruits and propagules are carried from one place to another through one agent or the other.
Agents of Weed Dispersal
The agents of weed dispersal include the following:
- Man and animals
- Explosive mechanism
- Farm tools, machines and implement.
Weed Dispersal by Man and Animals
Weed seeds such as Desmodium and Triumphetta possesses adhesive hook or sticky structure on their walls with which they stick to passing people or skin of animals and hence are carried to other places. The seeds are scattered about when they are brushed away.
Rodents and birds carry edible fruits of weeds from one place to another or when these get scattered in faeces and droppings of those animals and birds.
Weed Dispersal by Water
The fruits of weeds dispersed by water are normally water proof and they are light and hollow which enhances their ability and strength respectively. E.g seeds of some legumes and some grasses. Examples are wild cotton and water lily.
Weed Dispersal by Wind
Some weeds have fruits/seeds with special structures which adapt them to wind dispersal e.g.
- They are usually small and light in weight.
- They have floss and pappus.
- They have fluffy cotton outgrowth.
- Seeds are flat and sometimes covered with hairs.
Examples of weeds that can be dispersed by wind are Aspilia, Tridax, Siam weed, etc.
Also, when wind blows gently or violently against the head of Emilia weed, the fruits are detached and the pappus hairs assist them to float in the atmosphere and transported to another location.
Weed Dispersal by Explosive Mechanism
Some weeds possess pods which when dry explode and scatter on the field. This explosive mechanism also exist in weeds whose fruits are capsule. Examples are calopo, pueraria, centro, sida weed, Spigelia anthelmia (Pink weed), etc.
Dispersal of Weeds by Farm Tools, Machines and Implements
Farm tools such as hoes, cutlass and machines and implements such as tractors, plough, harrow and ridger used in bush clearing and land preparation may have seeds of weeds stuck on them. If these tools and implements are not properly cleaned and washed before been used on other farm they may transfer seeds of weeds to new area.
The topic is presented step by step
The class teacher revises the previous topics
He introduces the new topic
The class teacher allows the pupils to give their own examples and he corrects them when the needs arise
- Highlight and explain four methods of weed dispersal.
- List three features of weeds that can be dispersed by wind.
The class teacher wraps up or conclude the lesson by giving out short note to summarize the topic that he or she has just taught.
The class teacher also goes round to make sure that the notes are well copied or well written by the pupils.
He or she does the necessary corrections when and where the needs arise.
Prepare for the next lesson by reading about
MEANING, TYPES AND CLASSIFICATION OF PESTS