Weed management

• Weeds - plants "out of place" in cultivated fields. A plant growing where it is "not desired".
• Weeds are no strangers to man. They have been there ever eince started to cultivate crops about 10,000 B.C.
• Weeds principally originated from two important and major arbitrarily defined groups.

  • By man's conscious effort
  • By invasion of plants into man created habitats
• Classification of weeds

  • Morphology
  • Life span
  • Origin
• Grasses - have only one seed-leaf (monocotyledons). Their leaves ar egenerally long and narrow with parallel veins (venation).
• all the weeds come under the family poaceae are called as grasses.
• Sedges - weeds belonging to the family cyperaceae. The leaves are long. Stems are usually solid and triangular. have a three-ranked leaf arrangement.
• Broadleaved weeds - Venation of the leaves may be parallel as in monocots or netted as in dicots.
• all dicotyledon weeds are broadleaved weeds.
• Annuals - weeds complete their life cycle in one year or less.
• Biennials - weeds that live more than one year but not more than two years.
• Indigenous weeds - All the native weeds of the country.
• introduced/exotic weeds - these are weeds introduced from other countries.
• Losses

  • Reduction in crop yield
  • Weeds as resveroirs of pests and diseases
  • interference in crop handling
  • limitation of crop choice
  • loss of human efficiency
  • problems due to aquatic weeds
• Beneficial effects

  • weeds as fodder
  • weeds as vegetables
  • weeds as manure
  • weed as fuel
  • weed as indicators
• Principles of weed control

  • prevention
  • eradication
  • control
  • management
• weed control methods are grouped into:

  • physical/mechanical
  • cultural
  • biological
  • chemical
• Mechanical methods

  1. Tillage
  2. Hand pulling/hand weeding
  3. digging
  4. sickling and mowing
  5. burning
• cultural methods

  1. field preparation
  2. crop rotation
  3. growing of intercrops
  4. mulching
  5. stale seedbed
• Soil applied herbicides - herbicide act through root and other underground parts of weeds.
• foliage applied herbicides - herbicide primarily active on the plant foliage.
• selective herbicide - when in a mixed growth of plant species, it kills some species without injuring the other.
• non-selective herbicide - it destroys majority of yreated vegetation.