aga142 chapter 6

• Pest


  Any living thing—a plant, an animal, or a microorganism—which attack plants and cause damage in several different ways
• Pests and diseases occur on nurseries because cultivated plants are more susceptible than their wild relatives
• Growing large numbers of the same species close together can encourage disease-causing organisms and pests to establish and spread rapidly
• Many plants are specifically bred for their foliage and flowers rather than disease resistance, and commercial crop production can create environmental conditions that favour particular pathogens and/or pests
• Infectious organisms are part of the environment. The management of some crops, particularly those for same season sales, can lead to stress and susceptibility
• Understanding the crop being grown which include the normal growth habits and the normal variability of plants will help farmers to recognise unusual conditions as early as possible
• Categories of pests based on occurrence

  • Regular pest
  • Occasional pest
  • Seasonal pest
  • Persistent pests
  • Sporadic pests
• Categories of pests based on level of infestation

  • Epidemic pests
  • Endemic pests
• Categories of pests based on groups

  • Defoliators
  • Sap-sucking pests
  • Gall forming pests
  • Shoot boring pests
  • Stem boring and cutting pests
  • Root feeding pests
• Defoliators


  • Insects that feed on leaf tissues, including leaf-mining insects, leaf tiers and leaf rollers, and leaf skeletonizers
• Symptoms of defoliation

  • Large amount of missing foliage, normally uneaten parts of leaves common, browning of leaves, silk shelters and web enclosing foliage, insect remains including larval skin, branch mortality
• Sap-sucking pests


  • Suck liquid or semi-liquid material from leaves, stems, roots, fruits, flowers or even seed, affect tree vitality by extracting sap, can coat surfaces with honeydew leading to sooty mold growth, provide access for pathogenic fungi, and transmit viruses
• Symptoms of sap-sucking pests

  • Discoloration of leaves or needles, curled leaves, honeydew and sooty mold, stunting of host plant, premature leaf drop, branch and tree mortality
• Gall forming pests


  • Cause unusual plant growths as a result of abnormal cell division and/or cell enlargements, can occur on all parts of the plant but most commonly on leaves, stems and buds, rarely result in host tree death but can cause severe dieback and branch breakage, reduce photosynthetic capacity
• Shoot boring pests


  • Attack the apical terminal or leader of the tree, resulting in irregular stem growth, multiple branching, stunted growth, bushy appearance, and malformed boles, can kill very young seedlings
• Symptoms of shoot boring pests


  • Small silky web in the axil, accumulation of resin around the tip, browning of tips and shoot mortality
• Stem boring and cutting pests


  • Wood and bark boring insects that attack seedlings, feed on the outer surface of the bark, tunnel into the inner bark or deeply into the sapwood and heartwood, can be recognized by the type of tunneling, frass, and staining
• Symptoms of stem boring and cutting pests

  • Drying seedlings, presence of earth tubes, piles of debris on the outside of finished wood, honeycomb wood boring damage and adult exit holes on the stem
• Root feeding pests

  • Insects that consume the fibres and smaller roots, bore in the inner bark, or suck the sap, most damaging in nurseries and young plantations where the trees have small and fragile roots, can cause poor seedling growth and even death
• General management of pests in nursery tree seedlings

  1. Good cultural practices like crop sanitation

  2. Destroying severely infested seedlings

  3. Application of white oil formulation

  4. Use of neem oil

  5. Mounting yellow and/or blue insect sticky traps

  6. Hand picking when pests are still in low numbers

  7. Application of appropriate pesticides

  8. Use an Integrated Pest Management (IPM) Approach
• Plant disease


  Anything that prevents the plant from performing to its maximum potential
• Classification of plant diseases

  • Abiotic (non-infectious) diseases
  • Biotic (infectious) diseases
• Abiotic diseases


  • Caused by external conditions rather than living agents, including extreme temperatures, wind, drought or flood, moisture, frequent and heavy rain, soil compaction, excess or deficiency of nutrients, improper water management, and chemical injury
• Biotic diseases


  • Caused by living organisms, such as bacteria, parasitic plants, viruses, fungi, or nematodes, can replicate inside or on a host plant and spread from plant to plant
• Plants can be afflicted by multiple disease-causing agents at the same time
• A plant that is suffering from nutrient insufficiency or an imbalance between soil moisture and oxygen is frequently more susceptible to pathogen infection, and a plant that has been infected by one disease is often vulnerable to secondary pathogen invasion
• Disease complex


  A collection of all disease-causal agents that afflict a plant
• Symptom

  An observable consequence of plant disease on the plant, such as a discernible change in the plant's colour, function or shape
• Common symptoms of fungal diseases


  • Leaf rust, birds-eye spot on berries, seedlings damping off, chlorosis, stem rust, leaf spot, Sclerotinia
• Common symptoms of bacterial diseases

  • Bacterial ooze, water-soaked lesions, bacterial streaming, fruit spot, crown gall, leaf spot with yellow halo, canker
• Symptoms of viral diseases

  • Malformations, necrosis, wilting, annular stripes and spots, dwarfism, growth retardation, discoloration
• Viruses, crops affected and damage caused


  • Tomato mosaic virus, tobacco mosaic virus, cucumber mosaic virus, potato virus Y, potato leaf roll virus
• General cultural practices for fungal and bacterial disease prevention

  1. Do not reuse growing media

  2. Keep hose nozzles off the ground

  3. Use new or disinfected containers

  4. Quarantine all new plant material

  5. Remove infected plants and plant parts

  6. Maintain plant vitality

  7. Prune to improve air flow

  8. Apply proper chemical treatments

  9. Grow resistant plants

  10. Avoid irrigation extremes

  11. Monitor weather data and scout regularly

  12. Maintain good records

  13. Dispose of diseased material away from growing area
• General management for viral disease prevention

  1. Exclusion or avoidance

  2. Reduction in virus spreading sources

  3. Protection of the host plant
• Pest and disease management

  1. Apply proper chemical treatments

  2. Grow resistant plants

  3. Avoid irrigation extremes

  4. Monitor weather data and scouting reports

  5. Maintain good records of observations

  6. Dispose of seriously diseased plant material away from growing area
• Integrated Pest Management (IPM)


  An effective and environmentally sensitive approach to pest and disease management that relies on a combination of common-sense practices
• Components of IPM approach

  • Cultural control
  • Biological control
  • Behavioural manipulation (mechanical)
  • Host plant resistance
  • Chemical control
• Cultural control

  • Agronomic practices like applying organic matter, good spacing, crop sanitation, rouging, soil solarisation, insect sticky traps
  • Multiple cropping techniques
• Biological control

  • Use of natural living organisms like parasitoids and predators
  • Use of organic chemicals like plant extracts
• Behavioural manipulation (mechanical)


  • Use of naturally secreted substances like pheromones
  • Use of traps and barriers