Control Emerged Pigweed Prior to Planting Soybean

Newly Emerged Pigweed

Soybean planting is underway in many parts of the Delta and I have already received a number of calls about pigweed already being emerged in some fields. Most of the pigweed are in locations where glyphosate did not control the pigweed last year. So we should probably assume that they are resistant to glyphosate.

It is absolutely imperative that these emerged pigweeds are controlled prior to planting. Early weed competition can significantly impact soybean yields not to mention we don’t have many options to control emerged pigweed in soybean. One of the better options we have prior to planting soybean is paraquat. Prior to soybean emergence apply 2 pints of Gramoxone Inteon per acre for 1-3” pigweed, 3 pints for 3-6” pigweed and 4 pints for >6”. Be sure to include a nonionic surfactant or crop oil concentrate to the spray solution and use high water volumes (10 -20 gallons of water per acre) to ensure thorough coverage.

Hopefully a residual herbicide will be going out with these at planting treatments to prevent additional emergence of pigweed after planting. A list of residual options to control pigweed in soybean is available on our website at http://msucares.com/crops/weeds/pigweed.pdf. It is my opinion that you are taking a huge economic risk if you do not use a residual herbicide in fields known to have glyphosate-resistant pigweed.

If no residual herbicides are utilized, or if no activating rainfall occurs after application, plan on scouting fields very closely after soybean emergence and be ready to make an application of Flexstar or Prefix before pigweeds reach 4” in height. Be timely as you will only get one shot at controlling this weed. Label restrictions do not allow multiple applications of Flexstar/Reflex containing herbicides in a single growing season.

If we miss the pigweed with residuals or postemergence options our only option then is to hand weed or start over!! The University of Georgia reported that over 50% of their acres were hand weeded for pigweed last year costing the state millions of dollars. I hope it does not come down to this in Mississippi.