Thematic Discussion: Weeding versus Herbicides

Weeds management is far more complex than the two extremes of herbicides vs. tilling. There are often social/economic reasons for choosing one method over another. Conservation agriculture is a means to achieve productivity gain – there are flexible systems which can include the introduction of cover crops. Balance should be sought in striving for the least amount of tillage possible.

Recurring topics

There are a variety of reasons for choices made, such as:

  • Terrain that makes tillage impractical
  • Farmers may not have access to chemicals or the knowledge regarding their use
  • Increases in costs of labor
  • Non-residual herbicides that can contaminate water
  • Loss of efficacy due to overuse of herbicides
  • "if . . . then" scenarios such as farmers planting late in order to delay weed growth


  • Tropical conditions can greatly impact results that have proven effective in other areas;carbon content must be maintained through dry matter input
  • Legumes are a popular and effective cover crop but farmers tend to harvest them if they look good
  • Soil fertility is important and can be achieved with the addition of lime and phosphorus but they are not always easily obtainable

Processes and products

  • Effective resistance management can be obtained by using herbicides to manage cover crops which can then be used to suppress weeds
  • Timing of herbicide application is critical; most effective when weeds are stressed
  • Waiting for maturity keeps residue on top
  • Intercropping can offer a solution but if one planting does not emerge, the rows are narrow and only a small hoe can be used to remove the weeds
  • Genetically modified organisms (GNOs) are controversial but do have value; there are growing anti-GMO movements and some countries refuse to use GMOs but will accept aid from other countries that do use them


  • Control should be in the hands of the farmers
  • Research must be systems-oriented; all components should be looked at to predict how it can work together
  • Weed populations evolve over time and can also be affected by crop rotations; there is a transitory period during which some conclusions can be drawn based on patterns
  • Cover crops play a role but does not constitute an entire system; the keys are adaptive management and research with integrity