Skip to content

DISEASES OF CROPS | MEANING, CAUSES, EFFECTS, CONTROL

MEANING AND CAUSES OF DISEASE

A crop is a plant cultivated by man for a specific purpose. A plant disease is a deviation of the plant from the normal state of health, presenting outward visible signs. Diseases are caused by pathogens and enhanced by some physiological factors.

 CAUSES OF DISEASE

Plant diseases are caused by pathogens. Pathogens are disease causing organism which passes through a regular cycle of development and reproduction. Examples of pathogens that cause plant disease are viruses, bacteria, fungi, parasitic worms and rarely protozoa. Some of these pathogens are carried by vectors and other agents.

Physiological factors such as nutrient deficiency in the soil, heat, presence of inorganic salts in the soil and soil moisture content has a major role to play in influencing plant susceptibility to diseases.

 

SELECTED DISEASE OF CROPS

Name Casual organism Method of transmission Symptoms and economic importance Prevention and control measure
Maize Smut Fungus (Ustilago maydis) Fungus spores deposited

on fruits

(i)   Reduced yield

(ii) Galls on ears, leaves and tarsels which later turn black

(i)    Destroy diseased plant.

(ii)  Use resistant varieties.

(iii)           Seed treatment.

Rice Blight Fungus (Piricularia oryzae) Airborne spores on leaves (i)   Small longitudinal red spots on leaves which turn grey or brown

(ii) Reduced yield

(i)    Use clean seeds

(ii)  Avoid heavy use of nitrogen fertilizers.

(iii)            Use resistant varieties

Maize Rust Fungus (Puccinis polysora) Airborne spores deposited on leaves (i)   Red spots on leave.

(ii) Reduced yield

(iii)        Death of crop.

(i)    Early planting

(ii)  Crop rotation

(iii)           Use resistant varieties.

Cercopora  a Leaf spot of Cowpea Fungus Through

Wind

(i)           Reddish brown spots on leaves

(ii)         Lesions on leaves

(iii)       Chlorosis

(iv)        Dropping or falling of leaves.

(i)      Spray with fungicides

(ii)    Crop rotation

(iii)  Plant resistant varieties.

Rosette disease of  Groundnut Virus By piercing and sucking insect (Aphid) (i)      Yellow leaves with mosaic mottling.

(ii)    Stunted plant with curled leaves.

(iii)  Wilting and death of plant.

(iv)   Shortening of the internodes.

(i)      Early planting

(ii)    Crop rotation

(iii)  Use insecticides

(iv)   Uproot and burn infected plants.

(v)     Use resistant variety.

Cassava Mosaic Virus (i)    Through piercing and sucking insect (whitefly)

 

(Bemisia nigerensis)

 

(ii)   Infected plant cutting

 

(i)         Mottling of leaves or leaf curl

(ii)       Distortion of leaves and stems.

(iii)     Vein clearing

(iv)     Stunted growth

(v)        Development of yellowish pale areas alternating with green patches on the leaves or mosaic pattern on the leaves

(i)      Use resistant varieties

(ii)    Uproot and burn infected plant

(iii)  Spray with insecticide to kill vector

(iv)   Use disease-free stem cuttings

(v)      Farm sanitation.

Leaf blight of Cassava Bacterium

Xanthomonas manihotis

(i) Infected     cuttings

(ii)  Rain splashing

(iii)     Insects

(iv)     Tools

(i)              Blighting of leaves

(ii)            Wilting of plant

(iii)          Falling off of leaves

(iv)           Reduced yield

(v)             Cabker of stem

(vi)           Die-back of stem

(i)           Use resistant varieties

(ii)         Use disease free cuttings

(iii)        Early planting

(iv)        Practise crop rotation

Cocoa black pod disease Fungus Phytophthora palmivora (i)  Rain splash

(ii)            Insects

(i)         Brown spots on pod

(ii)       Rottening of pods

(iii)     Entire pod turns black

(iv)      Low yield

(i)           Remove and destroy infected pods

(ii)         Regular weeding

(iii)        Spray with fungicides eg Bordeaux mixture

(iv)        Avoid over crowding of cocoa plants.

Coffee

Leaf rust

Fungus (i)  By wind

(ii)  By rain splash

(i)       Yellow or brown spot on leaves

(ii)     Orange powdery mass on the leaf

(iii)   Reduction in yield

(iv)   Dropping of leaves

(i)           Plant seeds from healthy plants

(ii)         Use resistant varieties.

(iii)        Spray with copper fungicides.

Black arm (bacterial Blight of cotton) Bacterium (i)    Through leaves

(ii)  Stems near the ground

(i)       Angular spot on leaves

(ii)     Boll rot

(iii)   Exudates from affected leaves

(iv)   Retarded growth and death of plant.

(i)           Seed dressing

(ii)         Uproot and burn infected plants

Root Knot of

 

Tomatoes/

Okra

Nematodes Nematodes in soil (i)       Knotting or galling of roots

(ii)     Retarded growth

 

(iii)   Early death of plant

(iv)   Reduction in yield

(i)           Soil sterilization

(ii)         Crop rotation

(iii)        Use resistant varieties

(iv)        Uproot and burn infected plants

Damping off Disease of Okra Fungus Infected soil (i)       Retarded growth

(ii)     Cells become water logged

(iii)   Gradual wilting of plant

(iv)   Death of plant

(i)         Spray with copper fungicide

(ii)       Use resistant varieties

(iii)     Sterilization of soil

Onion

Twister

Disease

Fungus (i)    Infected soil

(ii)  Water splash

(iii)  Infected bulb

(i)       Twisting of leaves

(ii)     Grey patches on leaves

(iii)   Reduction in yield

(iv)   Death of plant

(i)         Crop rotation

(ii)       Use resistant varieties

(iii)     Spray with fungicides

(iv)      Early planting

Stored produce mould fungicides Fungus (i)    Infected seeds or fruits.

(ii)  High humidity

(iii)      By Soil

(i)       Black mould on seeds and fruits

(ii)     Pungent smell.

(iii)   Sour taste

(iv)   Decay of seeds and fruits in store.

(i)           Proper drying of seed before storage

(ii)         Spray with

(iii)        Maintain low humidity in store

(iv)        Remove contaminated seeds before storage.

See also  ANATOMY AND PHYSIOLOGY OF FARM ANIMALS

 EVALUATION

  1. What is plant disease?
  2. List four common disease causing organisms.

 

GENERAL EFFECTS OF DISEASE ON CROP PRODUCTION

  1. Disease generally reduce the yield of crops
  2. They reduce the quality of crops
  3. They can cause malformation of parts of plants
  4. They can kill or cause death of a whole plant
  5. They cause reduction in the income of a farmer

 

WAYS BY WHICH DISEASE SPREADS ON CROP FARM

  1. By rain splash
  2. Through the use of contaminated equipment
  3. The use of infected planting materials
  4. Wind blowing pathogens to other crops
  5. Through animals
  6. Through insect vectors
  7. Through visitors to the farm
  8. Through weeds
See also  METHODS OF ADVERTISEMENT

 

GENERAL CONTROL OF CROP PLANT DISEASES

  1. Cultural method: the use of crop rotation, planting of resistant varieties, tillage practice, regular weeding, pruning etc. to control or prevent disease
  2. Biological control: this is the use of the natural enemy of the disease to reduce or totally eliminate the disease
  3. Chemical control: this involves the use of pesticides such as fungicides, nematicides, insecticides to prevent disease or control disease.

 GENERAL EVALUATION

  1. What are pathogens?
  2. List two examples of pathogens.
  3. List three physiological factors that makes plants susceptible to diseases.
  4. List five air borne disease of crops.

 READING ASSIGNMENT

Revision question 6 and 9 in Essential Agricultural Science for Senior Secondary Schools by O. A Iwena chapter 26, page 247.

 WEEKEND ASSIGNMENT

SECTION A

  1. The following are pathogens except _____. A. viruses B. bacteria C. fungi D. algae
  2. Maize rust is caused by ______. A. bacteria B. fungi C. virus D. nematodes
  3. Rosette disease of groundnut is caused by ____. A. fungus B. virus C. bacteria D. nematodes
  4. Cocoa blackpod disease is caused by ______. A. virus B. bacteria C. fungi D. nematodes
  5. Root knoll of tomato is caused by ______. A. nematode B. fungus C. bacteria D.virus

 SECTION B

  1. What is disease?
  2. List disease pathogens

2    Discuss briefly the cassava mosaic disease under the following headings

A. Casual organism B. Transmission C. Symptoms D. Control

See also

FLORICULTURE – ORNAMENTAL PLANTS | IMPORTANCE, SPECIES, CULTIVATION, SOURCES, MAINTENANCE

FOREST MANAGEMENT

MEANING OF PASTURES AND FORAGE CROPS | FULL EXPLANATION

LIVESTOCK PARASITES AND THEIR LIFE CYCLES

ANIMAL PROTOZOAN DISEASES | SYMPTOMS, TRANSMISSION, EFFECTS, PREVENTIVE AND CURATIVE CONTROL

 

Related Words

  • diseases of crops
  • diseases of crops ss2
  • diseases of crops and their management pdf
  • diseases of crops tnau
  • diseases of crops and their control
  • diseases of crops viral
  • disease of crops plant
  • disease of crops cereal
  • diseases of fruit crops pdf
  • diseases of field crops
SUBSCRIBE BELOW FOR A GIVEAWAY

Building & maintaining an elearning portal is very expensive, that is why you see other elearning websites charge fees. Help to keep this learning portal free by telling mum or dad to donate or support us. We accept grants, sponsorships & support to help take this to the next big level and reach out to more people. Thank you so much. Click here to donate

Leave a Reply

Your email address will not be published.

School Portal NG
error: Content is protected !!