What is weed and how can control it?

Any plant not sown in the field by the farmer and grow where they are not wanted is called a weed. Examples; a corn plant growing in a soybean field, tulip growing in the middle of a yard.

Classification of weeds:

• Narrow leaf

Narrow leaf or grassy weeds look and act like grass. The leaves are narrow, stand upright, and have parallel veins. When the seedlings sprout, they have only one leaf.

This is why grass can be mowed without killing the plant. Most grasses have fibrous root systems. Grasses have both annual and perennial species. Examples; Jangli palak, Billi booti, Bathu etc.

• Broad leaves

Broadleaf weeds are any weeds that don’t look and act like grass. Seedlings of broadleaves have two leaves that emerge from the seed. The veins of their leaves are netlike.

They usually have a taproot and their root system is relatively coarse. Broadleaves may be annual, biennial, or perennial. Examples; Jangli jai, Della, etc.

Detrimental Effects:

• Compete with crops for moisture, light, nutrients.
• Contaminate crops and their products e.g. off flavored milk.
• Weed seeds in a seed crop.
• Carry pathogens.

Beneficial Effects:

• Prevent erosion
• Provide food and cover for wildlife
• Reduce leaching of minerals
• Add organic matter

Eradication vs. Control:

Eradication

• • Killing every existing plant

• Destroying all reproductive organs

Control

• • Reducing existing plants.

• Presence of some weeds does not seriously interfere with the area’s economic us.

Prevention

• Use clean, weed-free seed.
• Use clean equipment.
• Grow weed-adapted crops.
• Watch for weed seeds in packing material or nursery stock.

Methods of Control

• • Biological

• • Mechanical

• Chemical

Biological Control

• Used to kill thorny shrubs
• Velvetleaf will wilt and die.
• No harm to crops or ornamentals
• Fungal Spores
  • Sprayed on rice crop
  • Weeds controlled within 7 to 10 days
  • As effective as herbicides
  • No damage to rice
• Allelopathy
• Plants produce chemicals
• Chemicals harmful to other plants
• Chemicals exude through plant roots or will be washed from leaves by rain

Mechanical Control

• Cultivation
  • Uproot and/or cut off roots
• Mulches
  • Layer of plant or artificial material on soil surface
  • Work by cutting off light source
• Burning (1800^oF)
• Flooding
  • Used on rice paddies

Chemical Control

• Herbicides
• Depend on rain to wash them into soils
  • Preemergence
  • Postemergence

Herbicide Types

• Contact
  • Kills the part of the plant that it touches (contacts).
  • Not carried throughout the plant.
  • Will not kill perennial weeds.
  • Example: Paraquat
• Systematic
  • Blocks metabolic activity.
  • Translocated throughout the plant.
  • Necessary to kill perennial weeds.
  • Example: Roundup
• Selective
• Kills one type of plant but not another.
• Some will kill broadleaves, but not grasses.
• Others will kill some grasses and some broadleaves, but not others.
• Example: Atrazine

All selective herbicides are systematic BUT not all systematic herbicides are selective.