Lecture 16
IPM and Weed Control in the Tropics

IPM is a system in which a combination of methods is used to maintain pest populations at levels that allow profitable crop production with minimal adverse effects on the environment.

Also called informed decision making:

  • The decision maker gathers as much information as is necessary to make the best decision on pest control for the particular situation.
  • To make these decisions the farmer must understand the crop, production practices, pests, and available tools.

    • The Underlying Premise of IPM

    It is a scientifically proven fact that when current production technologies are properly integrated and precisely managed, the production goals of immediate economic gain and long-term sustainability are mutually reinforcing.

    Nonchemical Pest Management Techniques

  • Cultural
  • Biological control
  • Resistant cultivars
  • Mechanical
  • Quarantines

    • Cultural

  • Tillage
  • Cultivar selection
  • Rotation
  • Mulches
  • Crop residue destruction
  • Spacing
  • Irrigation
  • Intercropping/strip
  • Planting date (timing)
  • Row orientation
  • Fertility
  • Cover crops
  • No till
  • Burning residues

    • Biological (Most useful for insects)

  • Conservation of natural enemies
  • Importing natural enemies
  • Mass culture and release of natural enemies
  • Biopesticides (insects, diseases, weeds)
  • Allelopathy

    		•

    Host Plant Resistance

  • Tolerance
  • Nonpreference
  • Physical resistance
  • Chemical resistance

    • Mechanical

  • Row covers
  • Physical pest deterrents

    • Quarantines

  • Exclusion
  • APHIS - exports
  • Restrictions
  • Sanitation

    • Steps in Successful Pest Management

  • Correct identification
  • Insects- Pest ID services
  • Weeds - ID resources manuals, keys, video
  • Diseases - Farmer knowledge
  • Nematodes - Symptoms
  • Vertebrates
    •
  • Understanding of pest and crop dynamics
  • Life cycle/mode of attack
  • Key pests - direct vs. indirect
  • Beneficials - predators, pathogens, parasites
  • Seasonality
  • Pest environment interactions
    •
  • Monitoring - methods to determine pest presence
  • Visual - Forecasting
  • Scouting - Plant damage assessment
  • Field mapping
  • Traps, pheromones, light, sticky, pitfall, sweeps, spore traps, indicator plants
    •
  • Economic thresholds
  • Don't apply control action unless you expect loss from pest to exceed cost of control action.
  • Economic threshold is pest density at which you need to implement some control measure to avoid economic loss.
    •
  • Choice of optimum pest control options
  • Management decision to control pest
  • Based on: ID of pest, biology of pest, number present - economic threshold
    •
  • Assess effectiveness of treatment and plan for future
  • Assess why it worked or did not work
  • Plan for future based on assessment
  • Keep good records
  • Consult with pest advisors and discuss future options
  • Long range program inputs and objectives necessary for an effective pest control program

    • Strategy

    Ask these questions

  • What will I lose if I do nothing?
  • What will I gain?
  • How well will this action control the pest? Is this action legal?
  • Will this action impact either positively or negatively other pests?

    • Answer them to your satisfaction before implementing a control

    Available Tactics:

  • Cultural
  • Biological - Previously listed
  • Mechanical
  • Quarantines
  • Chemical
  • Biorational
  • Combinations
  • None

    • Chemical

  • Types:
  • Insecticides
  • Herbicides
  • Fungicides
  • Nematicides
  • Rodenticides
    •
  • Classification:
  • Efficacy
  • Longevity
    •
  • Mode of Action:
  • Product Label:
  • Environmental aspects
  • Storage
  • Fate/carryover
  • Breakdown
  • Mixtures
  • Adjuvants
  • Environmental influences (rain, humidity, wind, soil, temperature)
  • Resistance/tolerance
  • Timing of application
  • Equipment
  • Safety

    • Biorational (Integration of Control Measures)

    IPM = integrated pest management
    ICM = integrated crop management

  • Insects
  • Pheromones, mating disruption, insect growth regulators
  • Sterile release
  • Weather
  • Irrigation
    •
  • Weeds
  • Flaming
  • Hot water
  • Environment
    •
  • Diseases
  • Weather
  • Resistance
  • Environment
    •
  • Combinations
  • Multiple IPM approaches for all pests
    •
  • None

    • Implication of IPM in the Tropics

    Principles are the same for temperate agriculture but control is more difficult due to lack of winter, warmer temperatures, high moisture all of which are conducive to pest proliferation.

    Weed Control in Tropical Horticulture

    Characteristics of Weeds:

  • Ability to reproduce via large number of seeds and/or rapid vegetative regeneration.
  • The ability to persist. Seeds can survive in the soil for long periods.
  • A broad genetic base allows weeds to adapt to varying environments.
  • Compared to most pests weeds have relatively low mobility.
  • Weeds generally lack host specificity.

    • Cost of Weeds:

  • Weeds reduce yields by competition for light, water and nutrients.
  • Weed removal results in high production costs.
  • Weeds reduce the quality of crop and livestock products.
  • Weeds can poison humans and livestock.
  • Weeds harbor pests which attack crops.
  • Weeds increase the cost of harvesting.
  • Aquatic weeds hinder water flow and increase irrigation costs.
  • Social costs of weeds in less developed countries are high since many people spend their entire life weeding.

    • In the tropics, it is important to keep weeds out of fields for as long as possible since weed growth is rapid and early season weed competition is most damaging to crop growth.

  • Example: Maize and beans grown in Mexico had maximum yields if kept weed free for first 30 days of season.
  • Garlic grown in Brazil had maximum yields if purple nutsedge was eliminated for first 13 weeks of season.

    • Yield losses due to weeds in tropics if weeds are not removed:

    Country Crop  
    Sudan Cotton 64-75%
    Peanut 61-80%
    Sorghum 35-46%
    Wheat 28%
    Rice 69%
    Cassava 75-94%
    Yams 22-91%
    India Maize 40%
    Brazil Okra 62%
    Garlic 89% (purple nutsedge)
    Tomato 53%

    Effects of Weed Densities on Crops:

    Very low weed densities can cause severe crop losses.
    Crop losses usually increase with increasing weed density; loss per weed decreases.
    In any one crop, each species of weed will result in a different crop loss at equal density.

    Other factors to consider:

  • Crop cultivar
  • Method of propagation
  • Time of planting
  • Crop density
  • Soil moisture
  • Soil fertility

    • Factors Affecting Weed Control in Tropics

  • Long growing season
  • Continual source of new seed
  • Dense foliage and rapid growth
  • Annuals often act as perennials
  • Many species - crops and weeds
  • Weed growth is rapid
  • Many different rainfall patterns
  • Many soil types

    • Methods of Controlling Weeds:

    Prevention - do not allow weeds to invade a field or a country.

  • National quarantine
  • Use of clean seed
  • Avoid transfer of weed in nursery stock
  • Clean equipment
  • Avoid manure, mulch, etc. from other farms
  • Keep irrigation ditches free of weeds

    • Categories of Weed Control

  • Physical tillage by humans, animals, machinery
  • Cultural crop rotation, mulches, burning, crop competition
  • Biological - weed control with insects, diseases
  • Genetic - breeding for crop resistance to herbicides (e.g. glyphosate resistance)
  • Chemical - use of herbicides

    • Some Considerations for Use of Herbicides in the Tropics:

    Weeds

  • Tolerant weed species
  • Rapid shifts in weed population
  • Different weed species at different elevations

    • Crop

  • Limited screening for crop tolerance
  • Environment affects herbicide activity

    • Costs

  • High for chemicals and equipment
  • Shortage of water for spraying (Africa)
  • Lack of precision in applying herbicides
  • Traditions of intercropping and hand removal

    • Solutions

  • New low cost equipment - rope wicks, wipers, (Herbi)
  • Integration of old methods with new

    • Types of Farms

  • Plantations - most sophisticated agricultural practices
  • Private Farms - less sophisticated, more hand labor
  • Subsistence Farmers - mostly hand labor, human intensive

    • Problem Weeds in Tropics and Subtropics

  • Purple nutsedge – Cyperus
  • Common bermudagrass – Cynodan
  • Barnyardgrass – Echinochloa
  • Jungle rice
  • Goosegrass
  • Johnsongrass
  • Guineagrass
  • Water hyacinth
  • Cogongrass
  • Lantana

    • Eight of 10 weeds are grasses or sedges, 5 are perennial grasses, all are found in the United States.

    Parasitic weeds

  • Striga (witchweed) – tropical Africa and Asia causes severe losses in sorghum, millet, maize, upland rice and sugar cane.
  • Orobanche spp. – Mediterranean area; causes loss in broad bean and tomato

    • Future

  • > Level of Development
  • Greater involvement of technology
  • Globalization
  • New standards
  • New practices
  • Improved IPM

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