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Rain Raises Soybean Herbicide Questions

University of Minnesota Extension, Stearns County News
May 25, 2017         
Source:  Dan Martens, Extension Educator
University of Minnesota Extension
Stearns, Benton & Morrison Counties


Rain Raises Soybean Herbicide Questions
By Dan Martens, University of Minnesota Extension

FOLEY, Minn. (5/17/2017) — This discussion is provided by U of M State Weed Scientist Jeff Gunsolus, IPM Specialist Fritz Breitenbach, and Regional Extension Educator Lisa Behnken.

TODAY’S QUESTION: Are soil residual herbicides necessary in late-planted soybeans? What are your options if Soybeans have emerged?

Some people might be asking the same question about corn. Using pre-emerge and residual herbicides on soybeans is a more recent practice. This is partly due to several weeds becoming resistant to some key post-emerge products; and weeds like tall waterhemp that can be a persistent problem because they geminate and emerge well into the summer. So this discussion relates to soybeans.

Most soybean pre-emerge herbicides with Site of Action (SOA) #14 must be applied within 3 days of planting. Some of these include Authority products, Fierce, Optill, OptilPro, Sharpen, Sonic, Surveil, Verdict, Valor, and Zidua Pro. These labels generally say you can expect severe crop injury if these products are applied after soybeans have begun to crack the soil or emerge.

Exceptions to this for SOA #14 products are Anthem Maxx and products which contain fomesafen such as Prefix, Warrant Ultra and some others. These products can be applied from cracking through the 3rd trifoliate stage of soybeans with activity on some emerged (<2 inch) broadleaf weed species and activity on later emerging weeds. Products that contain fomesafen such as Prefix, Statement, and Warrant Ultra can only be applied east of I29 and SOUTH of I94.

Herbicides with SOA #15 such as Dual II Magnum, Outlook, Warrant and Zidua only have activity on unemerged weeds. Dual II Magnum can be applied through the 3rd trifoliate. Zidua can be applied on V1-V3 growth stages. Outlook can be applied on V1-V5 soybeans. Warrant can be applied through the R1 stage of soybeans, although the optimal application period is V2 to V3 stage. These herbicides will NOT control emerged weeds. They could be tank-mixed with glyphosate or glufosinate for varieties with corresponding genetic tolerance traits.

There are other options for post-emerge herbicides that do not provide residual control benefits where that is needed. Again, beware of weed resistance issues. Be sure to check herbicide labels for further information about restrictions and rates when applying products post-emergence, and for any restrictions on additives, carriers and tank mix options. Ask about factors that contribute to injury risk.

Trade names are used here for clarity and education purposes only and do not imply endorsement of a particular brand or product over others. Likewise, exclusion does not imply non-approval.

Internet Users can do a search for “Minnesota Extension Crop News” to check for other information posted regularly about current crop issues. And in Benton, Stearns, Morrison, you’re welcome to call the County Extension Office for information and assistance.

CROP INSURANCE: In areas with persistently saturated soils, it might be useful for farmers with crop insurance to review information about replanting and prevented planting coverage procedures, dates, and coverage reduction schedules after the “full coverage” planting date is past. As we have learned in past years, livestock producers often need to continue to plant for feed needs as much as they can. It can also be important to include creditors in discussions about options you might consider. There can be economic factors to consider that are unique for individual farms.  
ALFALFA HARVEST ALERT.  During the week of May 21, many of the cooperating farms, kind-of to the south of St. Cloud have alfalfa at height and maturity stages where they are looking for weather and field conditions to harvest dairy quality hay. Where soils were suitable to drive on, some farmers started working on hay harvest on Wednesday and Thursday. As we move north, more farms will be watching for harvest opportunities during the week of May 28 and following. Farmers want to avoid rutting up fields badly. 

Internet users can check updates of field observations and testing by searching for “Minnesota Extension Crop News.” For more information, call Dan Martens, Benton County Extension at 968-5077 if a local call to Foley or 1-800-964-4929.


Benton County Master Gardener Plant Sale. Saturday June 3, 8 to 11 a.m. at Coborn's Grocery in Sauk Rapids. The sale ends sooner if plants are gone.

Stearns County Dairy Breakfast on the Farm. Saturday June 3, 7:30 to 12:30, at the Kuechle Farm near Eden Valley. Park and Ride at the Eden Valley Elementary School.  

Morrison County Dairy Breakfast on the Farm, Saturday June 10, 7:30 to 11:30 a.m. at Roerview Dairy, near Upsala.


Daniel Martens
Extension Educator, Ag Production Systems
(320) 968-5077
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