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Weeds and weed control

A weed is any plant that grows where it is not required and whose economic disadvantages outweigh the advantages. Weeds suppress the growing crops, competes for their nutrients and spreads some pests and diseases.

Identification of weeds.

Weeds may be identified using their botanical (scientific names) because they are internationally known and accepted. Vernacular names or common English names may also be used but they are only limited to small communities.Following are some of the common weeds found on our farms.

Suggested Learning activities

1. Learners to go round the school farm and collect and identify at least twenty (20) common weeds found.
2. Dry the collected weeds in a controlled environment to preserve their colour then mount them on full scarps or manila papers to make a herbarium.
3. Note the details of each of the weeds mounted on the papers as follows; i) Common and scientific name
ii) Short description of the weed.
iii) Habitat (area commonly found )
iv) Control measures 4. Classify the weeds according to their morphological characteristics. 5. Practice application of herbicides in a crop of carrots to control weeds.

Background information

One of the limiting factors in crops productions is the infestation of the plants which grow where they are not required. The presence of these plants that are out of place contribute, significantly to production costs in any farming enterprise.


 

Glossary on weeds and weed control

Allelopathic weeds- weeds that produce poisonous substances that suppress growth or germination of plants, for example,Cyperus rotundus (nut grass/ sedge). Noxious weeds-weeds whose cultivation is prohibited by law for example mathenge, and Cannabis sativa. Annual weeds- weeds that complete their life cycle within one year/season or less, for example black jack. Biennial weeds- weeds that complete their life cycle within two years / seasons, for example Spear thistle. Perennial weeds- those weeds that take more than two years to complete their life cycle, for example Couch Grass. Aquatic weeds- weeds that grow in water, for example salvinia. Leguminous weeds- weeds that are capable of fixing free nitrogen into the soil, for example Crotolaria spp. Wettable powders - Finely ground particles that are used in chemical control of weeds, for example. Atrazines and Duron Selectivity- Ability of a chemical to injure one plant while allowing another to escape. Contact herbicides- Herbicides that kill only part of the plant it comes in contact with. Translocated/ Systemic herbicides- Herbicides that kill the whole plant even if a small part of the plant gets in contact with the herbicide. Propagation - A process of production of new plants.

Galls- swellings on plant parts. Plant morphology- form or structure of something. Plant Anatomy- arrangements 0f tissues within the plant. Rogueing - uprooting a plant or weed. Mowing - Mechanical removal of shoots from weeds. Quarantine - Keeping away from other produce that may be carrying some dangerous weeds
 

Topic objectives

By the end of this lesson you should be able to

  • Define a weed
  • Identify weeds
  • Classify weeds
  • Explain the characteristics which make weeds competitive
  • State harmful effects of weeds
  • Control weeds
  • Exercise safety measures to oneself, to crops and to the environment while controlling weeds.

Weeds and weed control

Introduction

A weed is any plant that grows where it is not required and whose economic disadvantages outweigh the advantages. Weeds suppress the growing crops, competes for their nutrients and spreads some pests and diseases.


 

Identification of weeds.

Weeds may be identified using their botanical (scientific names) because they are internationally known and accepted. Vernacular names or common English names may also be used but they are only limited to small communities.Following are some of the common weeds found on our farms.

Common weeds

Oxalis (Sorel)

Scientific name: Oxalis latifolia. English name: Sorel.

Click on a name to identify the named weed.
 

Click on a name to identify the named weed.

Click on a name to identify the named weed.

Click on a name to identify the named weed.

Click on a name to identify the named weed.

Click on a name to identify the named weed.

Click on a name to identify the named weed.

Click on a name to identify the named weed.

Click on a name to identify the named weed.

Classification of weeds.

Weeds can be classified on the basis of: a) Growth cycle
b) Plant morphology

Growth cycle and morphology

Click on a name to open the cycle

Click on a name morphology to see the details

Competitive ability of weed

There are various factors which contribute to competitive ability of weeds. These are:

  • Successful means of propagation such ability to produce large quantities of seeds and successful means of seed dispersal
  • Excellent adaptability to the environment such as elaborate and extensive root system and short life cycle.

Weed control methods

Some of the methods used in weed control include;

  • Chemical weed control
  • Mechanical weed control
  • Cultural weed control
  • Biological weed control
  • Legislative weed control

Chemical weed control

This involves use of chemicals called herbicides to control weeds. A farmer spraying herbicide to control weed on the farm. Spraying of farm chemical should be done during a calm weather to prevent danger to other people and the environment.

Legislative weed control

This involves government laws and acts which prevent the introduction of noxious weeds in the country.

  • Act gives the power to declare a plant noxious weed, for example Mathenge weed was declared noxious weed on 30th October 2008.
  • The act gives the director power to eradicate or control noxious weeds.
  • The act gives the director power to penalize a person who is guilty under this act.

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 Weeds and weed control 

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 Weeds and weed control  

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 Weeds and weed control

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