Post-Harvest Weed Management

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Weed management is a year-round task that we need to take seriously if we are to stay a step ahead of the challenge. Fall harvest is a perfect time to assess weed pressure in each field as it is harvested. Palmer amaranth is the top-of-mind weed, but other weed species also need to be considered, such as morningglory, barnyardgrass, and marestail.

Post-Harvest Weed Management Strategies

Weed control after harvest can be an essential component of an overall weed management strategy. Controlling weeds after harvest can help spread out the workload prior to spring planting, and can help reduce weed seed production. During and after harvest, scout fields to determine the weed species present and control these weeds until temperatures are low enough to limit germination. Any summer annual weeds that were cut-off during harvest need time to produce new leaf growth prior to herbicide application. Weed management strategies can include:

  • Shredding of crop residue to create a mulch, especially after harvesting corn or cotton.
  • Application of a non-selective herbicide to control emerged weeds.1
  • Application of a residual herbicide, to prevent weeds from emerging.2
  • Some weed species like marestail are much easier to control in the Fall rather than in the Spring.
  • Multiple tillage operations may be used later in the fall to control small weeds (Figure 1).3

Keep in mind that post-harvest tillage may move weed seed towards the soil surface and encourage germination. To prevent the spread of weed seed, clean tillage equipment before moving to a new field.

Herbicide Options and Considerations

Several herbicide options are available to help provide post-harvest weed management. A non-selective herbicide may be used after harvest to kill vegetation in the field. When glyphosate-resistant weeds are present, one option is to use a labeled non-selective herbicide containing paraquat on emerged weeds. When using paraquat herbicides to manage tough-to-control weeds such as Palmer amaranth, apply early, in accordance with the applicable pesticide label, to help ensure consistent control. To broaden and lengthen weed management, a contact herbicide should be tank mixed with a residual herbicide. Refer to product labels for tank mix partners. Residual herbicide selection is critical since some products may remain active in the soil and may influence the selection of next year’s crop. Herbicide labels should be checked for plant back and rotational crop restrictions. Because of the array of herbicide products and strategies available, it is important to work with your local brand representative for the best options for your fields.

Keep in mind, following harvest, it is important to allow time for regrowth of weeds to occur before herbicide applications are made. Fields with weeds that set seed in the fall may have dramatically higher weed populations during the next growing season. Knowledge of the weed species in a field and the competitiveness, emergence pattern, and density of the weed community can be used to develop effective herbicide programs. Other management practices can be developed to minimize reduction in yield potential, herbicide resistance, and control aggressive weed species. Controlling weed populations post-harvest can help reduce weed populations from year to year and allow for more efficient use of herbicides and cultural practices during the growing season.

Sources: 1Stephenson, D. 2012. Louisiana corn: dealing with roundup-resistant pigweed after harvest. Louisiana State University AgCenter. http://agfax.com/. 2Mississippi Soybean Promotion Board. 2011. Fall tillage key to controlling weeds and disease in the spring. http://mssoy.org/. 3Eubank, T. and Bond, J. August 2012. Post-harvest weed control options. Mississippi State University Cooperative Extension Service. http://www.mississippi-crops.com/. Extension. MP-44. http://www.uaex.edu/ Web sources verified 10/1/2018. 181013130551 10052018MW