WEEDS AND WEED CONTROL QUESTIONS AND ANSWERS

WEEDS AND WEED CONTROL QUESTIONS

 This topic entails the following:

• Definition of a weed
• Identification of weeds
• Classification o weeds
• Competitive ability of weeds
• Description of weed control methods
• Harmful effects of weeds

 The following relevant questions and their answers in this topic will greatly motivate and help the  user to comprehend and understand the required concepts and practices:

1.  Study the diagram below and answer the questions that follow:

(a) Identify the weed

(b) Why is it difficult to control the weed?  

 (c) State the economic importance of the weed shown above

2.  The following is an illustration of a common weed of arable land

 (a) Identify the weed    (b) Why is it difficult to control the weed?  

 (c) State one harmful effect of the weed on crop production

 (d) Give two measures used to control the weed

3.  Below is a diagram of some common weeds. Study then and answer the questions that follow:-

 (i) Identify weed A and B  (ii) State two effects of weed B on crop production

 (iii) Give a reason why weed B is difficult to control

 (iv) State the effective method of controlling weed B  

4.  Give four methods of propagation which make weeds have a high competitive ability

 over crops

5.  The diagrams below show weeds:-

 Identify the weeds C and D

 (b) State why it is difficult to control weed C

 (c) State two economic importance of weed D

6.  (a) List any four types of weeds known to be poisonous to livestock

(b) At what stage of life cycle is best recommended to control weeds?

7.  State two disadvantages of using herbicides  

8.  a) Name four herbicides that can be used to control weeds in a field of maize  

 b) At what stage of growth of maize should the weeds be controlled by use of a post

emergence herbicides

9.    (b) Give an account of economic importance of weeds

10.  a) mention two factors that affect selectivity of herbicides  

11.  Listing specific examples of weeds describe their harmful effects in agricultural production

WEEDS AND WEED CONTROL ANSWERS

1.   Oxalis (sorrel)

 -(oxalis latifolia)

 b)- The weed contain builbs i.e Elaborate & extensive root system that support the plant.

  – Because it has rhizomes.

 c) State the economic importance of the weed shown.

 – Reduces yields of crops.

 – Increases cost of production.

 – It’s a livestock feed.

 – Fixation of nitrogen.

2.  (a)Couch grass Digetaria
Scalarum  ( ½mk)

 (b) Why is it difficult to control the weed?  

• It has got underground rhizomes which grow deep in the soil  ( ½ x 1pt = 1mk)

 (c) One harmful effect of the weed on crop production

• Competes with crops for nutrients/soil moisture and space resulting to low yields
• Increases the cost of production when controlling it  

 (d) Two measures used to control the wed  

• Use of appropriate herbicides

– Physical removal of rhizomes

3.  i)- A-Double thorn (oxygonium
sinuatum)  

– B- Coach grass (Digiteria
scalarum)

  ii) – Lower the quality of produce

• Lower yields
• Compete with intended plants for nutrients and water

 iii) Weed B is difficult to control as it has underground rhizomes

  iv) Can be effectively controlled by use of chemicals  

4.  Four methods of propagation which make weeds to have a high competitive ability over crops

• Availability to produce many viable seeds
• Ability to propagate vegetative –with bulbs, rhizomes
• Ability to regenerate woody stems-quickly
• Efficient means of propagation

Ability to remain viable in the soil for a long period of time

5.  Weed C – Nutgrass (Cyprus rotundus)  

 Weed D – Sow thistle (sonchus oleraceous)

6.  a) – Thorn apple  

• Sodom apple
• Oxalis
• Tick berry ( ½ x4=2 mks)

 b) – Before flowering to avoid spread through seeds

– Early stage before spreading underground organs  

7.  

• Requires skilled labour
• Have long residual effect which interferes with future crops

It is not environmental friendly/ pollutes the environment  

8.  a)

• MCPA
• 2 – 4 – D
• Bentazon
• Bromoxynil
• Linuron
• Loxyyril
• Atrazine
• Metrubuzin

b)  – 10 – 15cm high

 – 2 – 4 weeks after emergence

9.

• Complete for nutrients/ light/ space
• ACD as alternate host of insect pests
• Some produce poisonous substances
• Blocks water cords
• Lowers the quality of pasture
• Poisonous to man and livestock
• Parasites of desired crops
• Aquatic weeds affect navigation and water animals
• Increase the cost of production
• Cause irritation to workers
• Some have medicinal value
• Eaten by man and livestock
• Acts as soil cover
• Add organic matter in the soil

– Some are legumes

10.  a) two factors that affect selectivity of herbicides  

• Stage of plants growth
• Plants morphology and anatomy
• Mode of action
• Environmental factors (2×1=2mks)

11.  specific examples of weeds describe their harmful effects in agricultural production

• Compete with crops for nutrients spacing ,light, moisture lowering yield e.g. MacDonald’s eye etc
• Some are parasitic e.g. wihhweed
• Low quality of produce e.g. Mexican marigold lowering quality of milk/pigweed seeds in finger millet
• Poisonous to both man and livestock e.g. Dahira stramonium, Bracken fern
• Allirnate hosts for pests and diseases e.g. mallow weed –for cotton strainer
• Some are allelopallic/hinder germination e.g. Mexican marigold
• Block irrigation channel e.g. salvinia/water hyacinth
• Affect fishing and navigation-salvinia and water hyacinth
• Lower quality of pasture e.g. manyatta grass
• Reduce workers efficiency/irritate e.g. double thorn, shnging nelthe, devil’s horse whip