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

Disagreement

• 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

Conclusions

• 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