Subject :Agricultural science

Topic :

DISPERSAL OF WEEDS (WEED DISSEMINATION)

Class :

Basic 7 / JSS 1

Term :

Third Term

Week :

Week 5

Instructional Materials :

• pictures of weeds
• samples of weeds

Reference Materials

• Scheme of Work
• Online Information
• Textbooks
• Workbooks
• 9 Year Basic Education Curriculum

Previous Knowledge :

The pupils have previous knowledge of

 EFFECTS OF WEED CONTROL METHODS ON VEGETATION AND SOIL

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

CONTENT

1. Introduction
2. Meaning of Weed Dispersal
3. Agents of Weed Dispersal

Introduction

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:

1. Man and animals
2. Water
3. Wind
4. Explosive mechanism
5. 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.

Presentation

The topic is presented step by step

Step 1:

The class teacher revises the previous topics

Step 2.

He introduces the new topic

Step 3:

The class teacher allows the pupils to give their own examples and he corrects them when the needs arise

:

EVALUATION

1. Highlight and explain four methods of weed dispersal.
2. List three features of weeds that can be dispersed by wind.

Conclusion :

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.

Assignment :

Prepare for the next lesson by reading about

MEANING, TYPES AND CLASSIFICATION OF PESTS