Scout Palmer amaranth and hemp fields to prevent crop spread – AgFax

Palmer amaranth towering above the soybean canopy. Photo: Bill Curran, Pennsylvania State University

Palmer amaranth and hemp, resistant to various groups of herbicides, continue to spread in regions of Pennsylvania. Searching for new introductions or weed escapes in soybeans and corn before harvest is necessary to slow the spread of these species. The main identifying characteristics that distinguish Palmer amaranth and Palmer hemp from other pig plants include the presence of male and female plants, glabrous stems, and a unique flower structure.

We strongly encourage weeding, hand removal or mowing of small lesions of Palmer amaranth or waterhemp. Localized populations of these species found on headlands or field edges are likely to be new introductions. The additional costs associated with removal will prevent even greater labor, herbicide and crop loss costs in future years as populations continue to expand.

Populations that are distributed across fields probably indicate that these species have remained undetected for more than a year. Palmer amaranth and hemp typically produce between 20,000 and 80,000 seeds per soybean plant, and studies have shown that nearly all (>98%) mature seeds are retained on the plant at harvest. Thus, harvest represents a significant dispersal event where localized populations can spread within and across fields in a single year.

Consider these best management practices during combine harvest to prevent and limit the further spread of weed seeds:

  • Survey fields before harvest and determine which fields are infested with herbicide-resistant weeds
  • Harvest herbicide-resistant weed-infested fields or parts of fields last
  • If a combine or other in-field post-harvest equipment has recently been in a field with herbicide-resistant weeds, clean the equipment or use other equipment if available
  • Carefully and completely clean combine harvesters when buying used
  • Start cleaning the combine from the top and move from the header back
  • Use the air compressor to remove as much weed seed as possible from the combine, including the stone catcher, grain auger and tail handler
  • Deep cleaning of the combine follows Methodology of straw bales when moving from fields infested with herbicide-resistant weeds and at the end of the year

Waterhemp and Palmer amaranth plants that pass through the cutting bar at harvest can potentially survive and set seed, especially if fall weather conditions are favorable for regrowth. Consider postharvest applications of 2,4-D, dicamba, or paraquat herbicides to control regrowth of these species to prevent additional seed production. Continue to investigate the fields and take action if necessary.

Preventing weed spread is an important tool in the Integrated Weed Management (IWM) toolbox, and cleaning and postharvest management equipment today is worth the time and effort to prevent serious management problems in the future. Scout Palmer amaranth and hemp fields to prevent crop spread – AgFax

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