Tank Mixes with Roundup Ready

As growers gear up for the first full-fledged season of planting Roundup Ready sugarbeets, questions surface about what can be tank mixed with Roundup.

Thousands of acres of corn, soybeans and cotton have been treated with Roundup since the introduction of these Roundup Ready crops more than 10 years ago. One would expect that every fathomable tank mix combination with herbicides, insecticides and fungicides has been tried, and certainly many of them have.

However, there is not an abundance of information out there to tell a grower, crop advisor or fieldman about what they can and cannot or should not tank mix with Roundup. Moreover, little information exists for using Roundup tank mixtures on Roundup Ready sugarbeets.

Most of the information that does exist pertains to tank mixing other herbicides registered for use in sugarbeets with Roundup.


TANK MIXTURES WITH SOIL-ACTIVE HERBICIDES

Over the past five years our studies have included tank mixtures with Nortron, Outlook, Dual, Pyramin, Ro-Neet, Eptam and Treflan, although most of our work is with Nortron, Outlook and Dual.

We have not seen any glaring problems tank mixing Roundup with any of these herbicides. The only exceptions might be Nortron and Outlook for common lambsquarters control.

It is known that common lambsquarters is one of the weeds that can be difficult to control with Roundup. Over the years, we have observed slightly lower lambsquarters control with Nortron or Outlook tank mixed with Roundup.

In our 2007 studies, common lambsquarters control July 10 averaged 88 percent with Roundup Original Max + Nortron (32 fl oz/A) or Outlook (14 or 16 fl oz/A), although this was no worse than Roundup alone. Increasing the Nortron rate to 48 fl oz/A in combination with Roundup, or applying Nortron pre-emergence followed by Roundup Original Max postemergence or applying generic glyphosate (Helosate) + Ro-Neet postemergence improved common lambsquarters control to 95 percent.

One of the other tank mix benefits we saw in 2007 was green foxtail control. The field where this study was conducted had a heavy green foxtail population. Addition of herbicides with green foxtail activity improved late season green foxtail control compared to applying glyphosate (either Roundup Original Max or Helosate) alone.


TANK MIXTURES WITH FOLIAR-APPLIED HERBICIDES

Even less tank mix work has been done with postemergence sugarbeet herbicides. Broadleaf herbicides including Betamix, Progress, Stinger and UpBeet have not shown much improvement, if any, for controlling broadleaf weeds with Roundup.

Stinger is the lone broadleaf sugarbeet herbicide that could be beneficial with Roundup for controlling Canada thistle and possibly even volunteer potatoes. Because Roundup is effective for controlling most grasses, the grass herbicides Assure II or Targa, Poast and Select have not shown any improvement of control grass weeds when tank mixed with Roundup.

However, in one of our 2007 studies with the grass herbicides, we were able to effectively control volunteer Roundup Ready corn with these three herbicides.


TANK MIXTURES WITH OTHER PESTICIDES

In 2007, we began looking at tank mixing other pesticides, such as Asana XL, Lorsban and Mustang insecticides and Gem and Quadris fungicides with Roundup Original Max. Our studies were limited to looking at any effect there might be on crop injury and weed control. We did not evaluate these tank mixtures for insect or disease control.

From one year's data, we found no detrimental effect of these tank mixtures (see Table 1). The only minor concern that emerged from this study was that common lambsquarters control was not as good with the Gem and Quadris tank mixtures with Roundup at the early evaluation date.

By the later evaluation, lambsquarters control was as good as Roundup alone or with any other pesticide. We do plan to continue looking at tank mixtures with other pesticides in 2008.


LABELED TANK MIXTURES

The label for Roundup Power Max-which will be the primary glyphosate formulation for use in Roundup Ready beets-states, "Tank mixtures with other herbicides, insecticides, fungicides, micronutrients or foliar fertilizers may result in reduced weed control or crop injury and are NOT recommended for postemergence (in-crop) applications of the product over the top of Roundup Ready crops, unless otherwise noted in this product label, or in separate supplemental labeling or Fact Sheets published by Monsanto."

Currently, none of the other pesticides labeled for use in sugarbeets are listed on the Roundup Power Max label, with the exception of Dual II Magnum and Outlook, which are labeled for tank mixing and use in Roundup Ready corn. None of the other pesticides labeled for use in sugarbeets states that glyphosate can or cannot be tank mixed with any of these pesticides.

The bottom line is: when tank mixing anything with Roundup that is not specifically listed on the Roundup label or on the label of whatever pesticide tank mixed with Roundup, the liability of performance rests on the user.

If there are any questions about this, it's best to contact a representative from the chemical manufacturer for more information.


Editor's note: Morishita is a University of Idaho weed specialist located at the Twin Falls Research & Extension Center and can be contacted by calling 208-736-3616 or email at don@uidaho.edu.