Tennessee Soybeans: PRE Applied Residual Considerations

There have been a number of calls where folks have asked my thoughts on “creative” PRE applied herbicides for soybeans.  A number of them have been very good and have had me wondering  “why didn’t I think of that”?  Others ideas had me thinking “well good luck with that”.

A number of folks have asked about tankmixes of Boundary and Verdict.  This is a tankmix I had not thought of but makes a lot of sense.  Verdict can burn down any existing horseweed and help Boundary provide residual Palmer amaranth control. 

The main question is if Boundary and Verdict are used PRE is it over the limit of Dual Magnum to apply Prefix POST.  The season use limit for Dual Magnum is 2.7 pts/ year. Therefore if you use a qt of Boundary (1pt Dual Magnum) and Verdict (no Dual Magnum) PRE and a qt of Prefix (1 pt of Dual Magnum) POST, the field is well under the season use rate of Dual Magnum.

Other folks have thought about running low rates of PREs. Zidua is a very effective PRE herbicide for Palmer amaranth control.  However it is not when used at rates below 2 oz/A. Some folks have asked about 1.5 to even 1 oz/A of Zidua.

I have looked at this herbicide long enough to know it will provide disappointing Palmer control if applied at those low rates. The 1.5 oz rate might be okay if mixed with Dual, Verdict or possibly some other premix, but not alone.

The other main question is on metribuzin as a PRE. I am really favorable using this herbicide as a foundation in a PRE. That is why I mentioned it extensively during the winter meeting season. Metribuzin or any of the many premixes that contain metribuzin are effective for Palmer control. 

The rate is the main question. One really needs to be near 5 oz/A or better to provide any measurable Palmer residual control. Most of the premixes that contain metribuzin when used at their typical use rates will provide between 4 and 6 ozs/A metribuzin depending upon the premix.

Examples of premixes that contain metribuzin rates closer to 5 oz/A or more and are widely used would be Boundary, Authority MTZ, Intimidator and Trivence. However, be cautious on sandy soils or eroded hillsides as any rate above 4 ozs/A can be very hard on soybeans that have poor metribuzin tolerance.

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To help make that decision, check for soybean variety tolerance to metribuzin at the University of Arkansas site.

Finally, there are a lot of new generic premixes out there. While all the name-brand premixes have been extensively vetted by Mid-South extension weed scientists a good number of the generics, though not all, have not. 

If you are considering using one of these, please ask these questions:  Is that Dual in the tankmix Dual Magnum or just Dual?  If it is just Dual then the rate had better be 1.3 pts to provide residual control comparable to 1 pt of Dual Magnum. 

The other big question is what rate of metribuzin is in the premix? If it is less than 4 oz/A, in my opinion, it is a short rate and will likely not provide the residual control you are wanting.