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. Velvetleaf and wild mustard were also present at lower populations.
• Within two weeks of planting and PRE herbicide application there was 1-inch of precipitation. This rainfall provided some incorporation of the PRE herbicides, to help manage some of the smaller seeded broadleaf weeds. There were some initial differences between the PRE treatments based on precipitation.
• Soybean injury:
o Soybean injury ranged from 0 to 31%, 31 DAP, however by 35 DAP soybean injury was less than 10% for all but one treatment.
o The POST herbicides provided varying levels of soybean injury. The treatment that caused the greatest amount of injury 14 DAT was Harmony + Cobra + Select Max (28%). Injury to most of the other treatments ranged from 10-15%, this is injury that is commonly observed with PPO-herbicides, like Cobra, Flexstar, and Ultra Blazer.
o Injury from the POST herbicides was not apparent at the next evaluation.
• Weed control:
o Weeds that escaped control from the PRE treatments were annual grasses, common ragweed, and some common lambsquarters.
o The POST herbicides provided varying levels of control of the annual grasses and common ragweed.
o By 28 days after the POST treatments, all but seven treatments provided greater than 90% control of all weed species. In most cases 12 fl oz/A of Select Max with a crop oil concentrate was needed for effective POST annual grass control.
o Common ragweed control was the species that was the least consistently controlled >90% with the PRE followed by POST programs. The fact that the common ragweed population was Group 2 (ALS)-resistant was the most challenging issue with some of the POST treatments. Additionally, Ultra Blazer, Cobra at 8 fl oz/A applied to slightly larger common ragweed, and Marvel failed to control common ragweed greater than 90%.
o At the end of the season, 18 of the 25 herbicide programs provided >80% weed control for all weeds.
• Herbicide program costs:
o The total herbicide program costs ranged from $43.33 to $86.61, these costs included application costs.
• Yield and economic returns:
o Soybean yield ranged from 26.5 to 59.6 bu/A for all herbicide treatments.
o Eleven of the 25 herbicide programs were amongst the highest yielding programs.
o All of the higher yielding programs were amongst the programs with the highest economic returns.
o Yield was more of a factor for economic returns than herbicide program costs.
o Yield appeared to be mostly affected by common ragweed and in one case common lambsquarters 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 28 at the MSU Agronomy farm. Over 280 growers, agronomists, sales representatives and extension educators attended this field tour. Additionally a specific non-GMO soybean tour was held that afternoon with over 35 growers of non-GMO soybean in attendance.
• There is one meeting 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.