PLANT DISEASE MANAGEMENT FOR Tropical CROPS

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PLANT DISEASE MANAGEMENT FOR Tropical CROPS

• DEPARTMENT OF CROP PROTECTION
• UNIVERSITY OF AGRICULTURE, ABEOKUTA

ENIKUOMEHIN, O. A. (Prof)
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INTRODUCTION

• A plant disease is any disturbance that prevents
  a plants normal development and reduces its
  economic or aesthetic value.

• Diseases can be caused by biotic (living) and
  abiotic (non-living) agents.
• Disease as a natural phenomenon.

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AGENTS OF PLANT DISEASE

• ABIOTIC AGENTS (factors) of plant disease
  include
• Environmental factors e.g. cold, heat, wind or
  lightning injuries, excessive moisture, drought
  etc.
• Mechanical factors e.g. cultivation damage,
  pruning damage, etc.
• Cultural factors e.g. improper planting, over
  mulching, over watering, over fertilization etc.
• Pesticides use e.g. herbicide, fungicide and
  insecticide damage.

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• BIOTIC AGENTS of disease includes
• FUNGI
• These are the most common cause of plant disease.
  They are microscopic organisms that feed on
  living plants and/or dead organic matter.
• They propagate thorough air-borne, water-borne,
  spores or drought resistant and tolerant
  sclerotia and/or mycelia. Insects, birds, man
  and equipments can facilitate dissemination of
  the fungal propagules (spores/sclerotia/mycelia).
  
• A wound on a plant readily helps the invasion of
  a healthy plant by fungi.
• Some fungi however, have the ability to infected
  intact (unwounded) plants.

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Symptoms of fungal diseases include leaf spots,
blights, wilts, root and/or crown rots, abnormal
growth, seed discolouration and malformation etc.
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• BACTERIA
• These are single-celled microscopic organisms.
  Some attack plants and cause diseases.
• Bacteria can be carried from plant to plant in
  droplets of water or by wind, rain splash,
  insects and equipments.
• Bacteria often survive between seasons on crop
  residue, seeds, cuttings or weeds.
• In warm and wet conditions, bacteria reproduce
  rapidly.

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Bacterial disease symptoms are similar to fungal
disease symptoms but the surfaces and/or
periphery of bacterial infected tissues are
usually watery.
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• VIRUSES
• These are the smallest parasites causing plant
  disease and can only seen through the electron
  microscope.
• Most viruses are spread by certain types of
  insects (vectors).
• The conditions that favour large number of insect
  vectors often lead to severe virus outbreaks.
• Most viruses survive between seasons in live
  plant tissues (weeds, seeds, cuttings).

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Symptoms of viral infections include stunting,
colour changes in leaves, growth distortions and
malformations.
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Principles of Plant disease management

• Exclusion (Quarantine) This means keeping out
  any material (plant) or objects (equipments) that
  are contaminated with pathogens or diseased
  plants and preventing them from entering the
  production system.
• Avoidance This means ensuring that crop
  production is undertaken at a time and/or place
  that makes the plant escape (avoid) the disease.
  
• Protection This means treating a healthy plant
  before it becomes diseased.
• Eradication This involves elimination,
  destruction or inactivation of existing inoculum
  or vector (agent/carrier) of disease.
• Resistance This is the use of crop varieties
  that have inherent genetic make up that forestall
  or reduced disease development.

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Common Practices for disease management in
organic systems

• Seed sorting Hand sorting of diseases seeds
  before planting and the use of salt density in
  seed sorting (where applicable).
• Use of seeds dressed with organic biocides for
  planting to reduced pre and post-emergence
  disease as well as disease transmission to adult
  plants.
• Destroying residue of previous crop by tilling as
  far in advance of planting of the new crop as
  possible.
• Appropriate planting date (time), population
  density (spacing), crop mixtures (intercropping)
  must be done to facilitate disease escape, reduce
  inoculum build-up and transfer.
• Monoculture promotes build up of pathogen
  population, so, it is important to follow a good
  rotation sequence. That is to avoid planting the
  same crop year after year. This use of non-host
  crops in the rotation sequence or intercrop
  provides time and space respectively, for decline
  in inoculum.
• Use of resistant varieties and disuse of known
  susceptible ones.

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• Good crop sanitation such as weeding and wide
  boarder rows.
• Solarisation To reduced disease caused by
  soil-borne pathogens cover soil with transparent
  polythene for up to 15 days. This reduces the
  amount of infective fungal inoculum in the soil.
• Removal (Roughing) of disease crops or plant
  parts early to forestall being a foci of
  infection of other crops or plant parts.
• Application of organic protection agents or plant
  products (ash, extract, etc.) to reduced disease
  incidence and severity. Insect vectors can be
  deterred by intercropping with plants with
  adverse olfactory effect on the insect species.
• Harvesting at optimum periods to reduce inoculum
  build-up on mature crops (seed) and at the ideal
  physiological maturity to enhance storability.
• Ensure balanced soil fertility status via
  application of cured and verified manure/compost.
  Avoid high salt accumulation, excessive manure or
  organic waste application, water logging and
  drought

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Plants with potentials for use in disease
management
Seed sorting with salt density - Rice and
other similar grains 10 salt concentration
(100g/L) - Sesame 5 salt concentration
(50g/L) - Cowpea 15 salt concentration
(150g/L)
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CONCLUSION

• It is important to correctly diagnose a disease
  before proffering management options.
• Diagnosis, being the process of determining the
  cause of a problem requires the attention of an
  expert.
• Although, experience and practice are very useful
  tools in plant disease diagnosis, it is advisable
  to employ the input of an expert at first
  instance prior to application of available
  management options.

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REFERENCES

• Enikuomehin, O. A. (2005) Cercospora leaf spot
  disease management in sesame (Sesamum indicum L.)
  with plant extracts. J. Trop. Agric. 43(1)
  19-24.
• Enikuomehin, O. A. (2008) Seed sorting of sesame
  (Sesamum indicum L.) by salt density and
  seedborne fungi control with plant extracts.
  Arch. Phytopath. Plant Prot. D0I
  10.1080/03235400801940175.
• Baniecki, J. F. (2009) Plant disease facts.
  www.wvu.edu/agexten/ipm/disease/pHdisfc.htm(view11
  /3/2009)
• Koike, S. T., Gaskell, M., Fouche, C., Smith, R.
  and Michell, J. (2009) Plant disease management
  for organic crops. Organic vegetable production
  in California series. Publication 7252 6pp
  (available on www.sfc.ucdavis.edu).
• Stoll, G. 2001. Natural crop protection in the
  tropics. Letting information come to life. F
  T. Mullerbader Fildstadt Publishers, Germany,
  208p.

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