Results and observations:
• The weed populations at the MSU Agronomy Farm were heavy infestations of annual grasses (mainly giant foxtail and yellow foxtail), common lambsquarters, and common ragweed. Powell amaranth, velvetleaf, and wild mustard were also present at lower populations.
• Within one week of planting and PRE herbicide application there was 1.16-inches of precipitation. This rainfall provided some incorporation of the PRE herbicides, to help manage some of the smaller seeded broadleaf weeds. Conditions became extremely dry less and rainfall was less than 1-inch through the end of July. There were some initial differences between the PRE treatments based on precipitation.
• Weeds that escaped control from the PRE treatments were annual grasses, common ragweed, and some common lambsquarters.
• Sixteen of the 20 treatments needed to be treated POST by 30 DAP. The remainder were treated four days later.
• The four PRE treatments that provided slightly longer residual control were Fierce XLT, Sonic + Boundary, Zidua PRO, and Prefix + Metribuzin.
• Soybean injury was relatively minor from the PRE treatments due to lower precipitation, with the exception of Fierce XLT, 14% injury within 28 DAP.
• Due to the dry weather and overall poor control this year, several different POST treatments were examined. These programs can be found on the web-accessible factsheet.
• The POST herbicides provided varying levels of soybean injury and control the annual grasses and common ragweed.
• Soybean injury:
o Some of these herbicide treatments caused significant leaf burn.
o Soybean injury from the POST treatments ranged from 0 to 26%, 14 DAT.
o Treatments with Cobra or Cadet generally provided the greatest soybean injury.
o All soybean recovered from POST herbicide injury by 28 DAT, with the exception of the two treatments that had two POST applications, Cobra + Select Max followed by Harmony (6%), and Cadet + Basagran + Select Max followed by Cobra (14%).
• Weed control:
o Dry conditions at the time of the POST application followed by later season rains that promoted late-season grass emergence affected overall weed control. Treatments that relied on a Group 2 herbicide (ALS-inhibitor) for common ragweed control were not effective, since the common ragweed population was resistant to ALS-inhibitors.
o By 56 days after the POST treatments, there were only two treatments that provided greater than 90% control of all weed species and four programs that provided greater than 80% control of all weed species. These programs included both PRE and POST herbicides that provided good control of annual grasses. In most cases 12 fl oz/A of Select Max with a crop oil concentrate + Flexstar or Cobra was needed for effective POST weed control.
• Herbicide program costs:
o The total herbicide program costs ranged from $42.93 to $83.17, these costs included application costs.
• Yield and economic returns:
o Soybean yield ranged from 30 to 79 bu/A for all herbicide treatments.
o Three of four of these programs were amongst the four highest yielding programs. The other had slightly lower common lambsquarters control. Four additional programs were similar to the second highest yielding program.
o All of the higher yielding programs were amongst the programs with the highest economic returns. There were two additional programs that were not amongst the highest yielding that were similar to the programs with the highest economic returns for a total of six of the 20 programs examined.
o Yield was more of a factor for economic returns than herbicide program costs, with the exception of one program that had two POST herbicide applications.
o Yield appeared to be mostly affected by annual grass and common ragweed control.
• Our recommendation when growing non-GMO soybean is to plan on a two-pass program (PRE fb. POST). These programs have consistently provided better weed control, yield, and economic returns, even with the added herbicide and application cost.
• This research was highlighted at the MSU Weed Control Tour held on June 29 at the MSU Agronomy farm. Over 300 growers, agronomists, sales representatives and extension educators attended this field tour. Additionally a specific non-GMO soybean tour was held that afternoon with over 40 growers of non-GMO soybean in attendance.
• There are two meetings scheduled in March where results from this research will be presented to growers and potential growers of non-GMO soybean. In addition, these growers have access to these results at http://www.msuweeds.com.