Weed management


Weed management

Weeds compete directly with the rice plants and reduce rice yield. Presence of each 1 kg dry matter of weeds is equivalent to 1 kg grain loss. Weeds cause maximum yield loss within the first 20–50 days after crop establishment. Weeding after panicle initiation may also be important to prevent shedding of weed seeds for future crops.

Direct control of weeds can be done through (1) manual weeding by hand and (2) mechanical weeding using implements such as push weeder and interrow cultivation weeders.


Manual


Manual weeding by hand is an efficient method for weed control. However, this is labor intensive and is not practical for large areas.

When to hand weed:

  • When weeding annual weeds and certain perennial weeds that usually do not regenerate from underground parts
  • When removing weeds within rows and hills where a cultivating implement, such as a push weeder, cannot be used

Handweeding of young weeds at the two-leaf to three-leaf growth stages is extremely difficult. To effectively hand weed:

  • Delay weeding for at least 2 weeks or until weeds are large enough to be grasped easily.
  • Ensure that there enough soil moisture for easy pull.
  • Remove the weeds from the field to stop them from regenerating.

Mechanical


Mechanical weeding is most appropriate for crops transplanted in straight rows. This method requires less time and labor costs to than manual weeding.

  • Ensure that there is enough soil moisture before weeding. It could be difficult to use a weeder when the soil is too dry.
  • Pass the weeder in between rows. This buries the weeds and cuts the root system so weeds die before they can re-establish. Improper use of weeders can damage the rice.
  • Plowing and harrowing in fallow fields should be undertaken at least 7–10 days apart during field preparation.
  • Good land levelling reduces weed growth because most weeds have trouble germinating under water.
  • Select varieties which have early vigour.
  • Use clean rice seed which is free of weed seeds.
  • Apply permanent water during early crop stage, as weeds cannot germinate under water.
  • First weeding begins within 2–3 weeks after establishment and the second in another 2–3 weeks. Weeding should be before fertilizer application.
  • Use herbicides after correct identification of weeds and use the appropriate rate of application as recommended on the label.
  • Apply pre-emergence herbicides after planting, prior to weed-emergence.
  • Apply post-emergence herbicides 15-25 days after sowing/days after transplanting at 2-4 leaf stage of weeds.
  • Herbicides are poisonous; if they are not used properly they can cause health and environment problems. Label them clearly and keep them out of children’s reach.
  • Always use protective clothing when spraying.
  • Do not wear raincoat when spraying as this increases sweating.
  • Avoid eating, drinking, smoking and tobacco chewing while spraying