Results and observations:
• The weed populations at the MSU Agronomy Farm were heavy infestations of annual grasses (mainly giant foxtail), common ragweed, wild mustard, and common lambsquarters. Velvetleaf was also present at lower populations.
• Within two weeks of planting and PRE herbicide application there was 2.4-inches of precipitation. Precipitation adequately incorporated all of the soil-applied herbicides, resulting good weed control and also substantial crop injury.
• Soybean injury ranged from 8 to 39% from the PRE herbicide programs, 30 DAP and from 0-29%, 45 DAP. The greatest injury occurred from Valor and/or chlorimuron combinations (with the exception 2.25 oz of Canopy). Additionally, significant injury occurred from Sonic tank-mixed with Warrant. The high soil pH (7.1) at this location may have influenced the greater injury from the premixtures with chlorimuron.
• Most PRE treatments provided excellent weed control of all species with exception of the annual grasses and common ragweed.
o At 45 DAP, the POST herbicide were needed for annual grass and common ragweed control.
• There were two treatments that were not treated with a POST herbicide application, since at the time the POST treatments were made weed control was over >89% for all weeds.
o These treatments were Valor XLT + Zidua and Trivence + Zidua.
• Several different POST herbicide programs were used to control annual grasses and common ragweed. These programs can be found on the web-accessible factsheet.
• Soybean injury:
o Soybean injury was greatest 7 days after the POST treatments (DAT). For the majority of POST treatments, soybean injury ranged from 24 to 41%. Soybean injury from the PRE treatments seemed to compound the effects of the POST treatments.
• Weed control:
o Ten of the 18 herbicide programs treated with a POST herbicide provided >90% of all weeds, 56 DAT. An additional 6 herbicide programs provided >80% weed control. There were only two programs that did not meet 80% weed control that were treated POST.
? Grass control was less than 80% with Fierce fb. Cobra. This treatment did not have substantial grass escapes at the time of the POST, but the PRE did not last throughout the season.
? Common ragweed control was poor when Basagran + Cadet were applied POST.
? The two PRE programs that did not have a POST application did not hold throughout the season and control was lower than 90% for common ragweed and annual grasses.
? Of the POST herbicides used for common ragweed control Storm, Marvel and Basagran + Cadet were the weakest.
• Herbicide program costs:
o The different herbicide programs costs, including application costs ranged from $38.70 to $72.90. The average herbicide program cost was $57.88.
• Yield and economic returns:
o If weeds were not controlled soybean yield was 24.4 bu/A, which was a 64% reduction in yield from the highest yielding treatment.
o Soybean yield ranged from 39.6 to 67.9 bu/A for all herbicide treatments.
o There were 11 of the 20 herbicide programs that provided high yields (not different from the highest yielding program). All of these treatments were also amongst the programs with top economic returns.
o Yield was more of a factor for economic returns that herbicide program costs.
o Yield appeared to be mostly affected by soybean injury in three instances and from weed control in four instances and potentially both in two instances.
• 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 July 1 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 February 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.