In conventionally managed fields, weed control is achieved with preplant and/or preemergence herbicides. Postemergence herbicides are applied after the field is cultivated to control broadleaf and grass weeds. Hand hoeing is done as needed.

In organic production systems, preplant irrigation induces weed emergence, which can be killed by tillage, flaming, or mulches (straw, cardboard, etc.). There are OMRI-approved organic herbicides (nonselective, contact) which have limited residual activity. Consult your certifying agent prior to applying organic herbicides.

Users should have a current chemical applicators license, and read and save copies of all labels. Herbicide options are listed in Table 6.5 and 6.6. 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. Always use the recommended amount of product, apply it as stated, and watch reentry intervals (REI) and preharvest intervals (PHI).

Herbicides are applied in the following ways:

• Preplant: incorporated into the soil prior to seeding or transplanting the crop.
• Preemergence: applied to the soil after planting but before the crop or weeds emerge.
• Post-transplant: applied after the crop is transplanted either before weeds emerge or after clean cultivation.
• Postemergence: applied to weeds after both weeds and the crop have emerged.