Weed Management

In conventionally managed legume fields, weed control is achieved with preplant and/or preemergence herbicides. Fields are often cultivated 4-6 weeks after planting, and then post-emergence herbicides applied to control broadleaf and grass weeds.

In organic production systems, manage weeds by encouraging weed emergence with irrigation, then kill these weeds with tillage, flaming, or mulches (straw, cardboard, etc.). There are OMRI-approved organic herbicides that can assist in weed management. These herbicides are nonselective, contact herbicides, and are applied to growing, green weeds. Most organic herbicides have limited residual activity and are used in combination with tillage, hoeing, and mulches. Consult your certifying agent prior to applying organic herbicides to ensure you stay in compliance.

For any herbicide application, keep a copy of the label, and ensure you have read it carefully. Different companies market similar products under different trade names, so use the chemical name (active ingredient) to ensure the proper material is applied. Only one representative trade name is listed in the Table 7.4. Herbicide labels change, so always consult a current label to determine: (1) if the crop is listed for herbicide use; (2) what precautions are required; and (3) what rates and application methods are allowed. It is a violation of federal law to use any herbicides for purposes other than those specified on the approved label. Off-label applications are hazardous to the environment, to people using the product, and can severely injure the crop.

Use the recommended amount of product and apply it as stated. Pay attention to re-entry intervals (REI) and preharvest intervals (PHI). Don’t spray in high wind conditions. Work with your neighbors, as many herbicides are toxic to other crops growing nearby. Finally, herbicides are just one tool available for weed control, and their use should supplement other good weed management practices.

Herbicides are applied to legumes in the following ways:

• Pre-plant or pre-plant incorporated: incorporated on the or into the soil prior to seeding the crop.
• Pre-emergence: applied to the soil after planting but before the crop or weeds emerge.
• Post-emergence: applied to weeds after both weeds and the crop have emerged. In some cases, sprays are directed to row middles and shielded from application to the crop. When using a postemergence herbicide, the entire weed must be covered for maximum control.