Weed control in no-till systems
The success of preemergence herbicide treatments depends on rainfall to activate the herbicide soon after spraying. Without moisture, herbicide performance suffers. Herbicides that are soil-applied after planting are often preferred over treatment prior to planting. Planter row-cleaners or "trash-whippers" can move herbicide-treated soil from the row to the row middles, creating weed problems in the untreated zone.
Two types of preemergence herbicide programs are common in no-tillage:
- a full season program--where herbicides control weeds throughout most of the growing season, or
- a short residual program--where the crop shades out later germinating weeds. Postemergence treatments may be necessary for weed escapes.
Weeds in no-tilled fields tend to germinate throughout the season. Maintain season-long weed control with early pre-plant treatments of "full season" residual herbicides or split treatments of herbicides with medium longevity. Split applications often include applying 1/3 of the labeled herbicide rate early and the remaining 2/3 at planting. Many early preplant herbicides have burndown activity on small weeds (1" to 3"). Adding a crop oil or surfactant to the herbicide mix improves their control. Weeds greater than 3", such as winter or early summer annuals, may be present at the time of early preplant applications. Abundant weed growth may require a burndown herbicide, such as glyphosate + 2,4-D, paraquat, or 2,4-D.
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