ISSUE 10   July 15, 2010


Question via email: I had a gentleman stop by my office a few minutes ago wanting to know about herbicides labeled for sweet corn. The Weed Control Guide does not specifically discuss weed control in sweet corn. I told him that the herbicide label would say whether or not you could apply it to sweet corn. He was wondering, and I guess I am too, if there are enough sweet corn producers in the state to make it worth discussing weed control in sweet corn in the weed control guide?

Answer: I have tried to keep everyone informed about resources out there for pest control in sweet corn. I usually send emails out through <agdakota> list serve each spring and put information in the Crop and Pest Report. As an Extension expert you should be automatically subscribed to both.

Since Wisconsin is the “sweet corn state”, their Extension Service has put together a pest guide for most vegetable crops including sweet corn. It is a free site and contains a weed guide that is very thorough, so rather than reinvent the wheel I just refer folks to that web site. It is updated each year. The pdf can be downloaded.



Here is an excellent sumary of published information correcting much mis-information about manganese (Mn) deficiency of soybeans with Roundup Ready trait, interactions of glyphosate and Mn within soybean, and interactions of glyphosate with Mn in the soil. Of couse our problem in ND and western MN is iron chlorosis, but some principles expressed in this article can apply. The author is Dr. Bob Hartzler, Weed Scientist at Iowa State Univ.

I thought you folks would be interested in the following article by Hartzler regarding Glyphosate-Manganese Interactions in Roundup Ready Soybean:

Manganese deficiency is occasionally observed in soybean grown in northern Indiana. Because Mn deficiency symptoms frequently appear near the time of post-emergence glyphosate applications in glyphosate-resistant soybean, producers and custom applicators occasionally  tank-mix glyphosate and foliar Mn fertilizer to reduce application costs. Research has shown that glyphosate efficacy is antagonized when it is tank-mixed with some Mn fertilizers and Mn-EDTA appears to be the least antagonistic of the Mn fertilizers.

Bill Johnson, Mike White and Glenn Nice, Purdue Extension Weed Science, conducted a greenhouse study to evaluate the effect of a couple of Mn fertilizers on glyphosate efficacy on velvetleaf and common waterhemp, two weeds which have shown variable tolerance to glyphosate. To conduct this study, they planted velvetleaf and waterhemp seeds in Styrofoam cups and allowed the weeds to grow to 4 to 6 inches in height. The treatments were applied with a greenhouse track sprayer calibrated to deliver 15 GPA. The glyphosate rate used was 11 oz/A or about half of the normal labeled rate. They used a low rate in an attempt to exaggerate the differences that can occur when spray conditions in the field are less than ideal (i.e. big weeds, drought conditions). The treatments were applied in either de-ionized water or in well water. The well water is considered hard water with significant concentrations of calcium and iron in it. The Mn fertilizer solutions consisted of 6 percent Mn Sulfate applied at 32 oz/A and 6 percent Mn EDTA applied at 36 oz/A.

Rich Zollinger
Extension Weed Specialist


Plants can survive a glyphosate application for many reasons.  The greater the diversity of species and the more uniform the response of plants surviving a glyphosate application the more likely plants are surviving due to reasons other than glyphosate resistance.  The greater the continuum of plant responses from dead to normal-appearing plants, especially when observed in just a single species, the more likely plants are surviving due to resistance.  Glyphosate resistance can be difficult to identify due to low level resistance.  A video demonstrating the continuum of plant responses was created to assist individuals in identifying glyphosate resistance.  The video is available at the following website:  At this website select “Scouting for Glyphosate Resistance”.  Two videos are available at the forwarded website.  The long version includes an introduction about resistance and demonstrates the continuum of plant response and the short version demonstrates the continuum of plant response.  If you suspect glyphosate resistance contact Jeff Stachler at or 701-231-8131.



Volunteer Roundup Ready canola can currently be observed in many fields.  Roundup Ready canola is likely introduced into a field as a contaminant in dry fertilizer and cover crops or dropping off rail cars on railroads.  Any method of control stopping seed production is important.  Most canola plants are currently in late reproductive stages making immediate removal necessary.  If seeds are produced volunteer Roundup Ready canola will become more frequent in fields.  At the current growth stage of the canola, no herbicide options are available for control in Roundup Ready sugarbeet, leaving hand-removal as the only option.  Complete control of late flowering canola in soybeans is not likely, although Flexstar should suppress additional flowering and potentially reduce seed production.  Consult the June 24th issue of the Crop and Pest Report for additional information on control of volunteer Roundup Ready canola (

Jeff Stachler
Agronomist - Weed Science

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