The delays this spring and early summer attributable to heavy rainfall, many of the corn and especially soybean fields that didn't get a foundation herbicide are starting to get a little, well for lack of a better term, UGLY.  With this in mind I thought a quick reminder of usage rates and tank-mix partners might be helpful this week.  I just hope we get a chance to use them.

Glyphosate can be applied over the top of Roundup Ready soybeans up to 1.5 lb ae/acre.  This is equivalent to 44 fl oz of Roundup PowerMax/WeatherMax, 48 fl oz of Touchdown Total or Durango DMA/Duramax, or 64 fl oz of most generic types of glyphosate.  You can use up to 66 fl oz of Powermax equivalent in your soybean crop (44 fl oz for corn).  Use the higher rates for perennials and large or hard to control annuals.

Glyphosate can be applied to RR soybeans from emergence through flowering (R2 stage - ends when a pod is 5 mm or 3/16 inch long at one of the four uppermost nodes on the main stem).  Include an appropriate surfactant if the product is not fully loaded and AMS for hard water or when tank mixing.  You can tank mix a number of products with glyphosate to broaden the spectrum.  Here are some suggestions:

  • For volunteer corn, common mixtures would include: Assure II, Targa, Fusilade, Fusion, Select, and others.  Rates will vary by products.
  • For increased broadleaf activity and/or for residual control, Classic, Harmony, FirstRate, Pursuit (or Extreme), Raptor, Scepter, Zidua, and Synchrony can be added.  Classic, Synchony, and FirstRate will help control glyphosate resistant marestail.  Classic and Synchrony added to glyphosate will help provide residual control of burcucumber.  Again, rates will vary by product.
  • Contact type herbicides such as Aim, Cadet, Reflex (or Flexstar GT), and others have been promoted in tank-mixture for improved control of certain glyphosate tolerant or resistant weeds (morning glory, nightshade, pigweeds, ragweeds, etc.).  Be aware that these herbicides can cause some leaf burn and also antagonize glyphosate performance on normally susceptible weed species.
  • Increased rates of glyphosate can help improve perennial weed control.  For weeds like pokeweed, be sure the spray boom is above the weeds and use spray tips that maximize coverage.
  • Finally, several residual grass herbicides can be tank mixed with glyphosate products.  Warrant is one of the newer products containing encapsulated acetochlor.  Both Dual and Outlook can be applied post, but only up to the third-trifoliate leaf stage.

With the continuing weather patterns, the potential for White Mold in our soybean fields is high.  Here is some information from Iowa State University reviewing management tips.


Managing White Mold in Soybeans

By Daren Mueller, Department of Plant Pathology and Microbiology
 

Farmers in the Midwest may be concerned about white mold (also called Sclerotinia stem rot) in soybeans this year.  The disease, caused by the fungus Sclerotinia sclerotiorum, is not common every year, but farmers who have battled the disease in the past will want to assess the risk of white mold development as soybeans approach flowering (growth stage R1 - plants have at least one open flower at any node).

Development
White mold development is favored by cool, cloudy, wet, humid weather at flowering. The disease is more problematic in soybeans in high-yield environments where high plant populations, narrow row spacing, and an early-closing canopy are commonly used. No single management strategy is 100 percent effective at eliminating white mold, and in-season options for at-risk fields are limited.   

There are fungicides available for in-season management of white mold however, not all commonly used fungicides are labeled for use against white mold in soybeans.  The NCERA-137 national soybean disease committee developed a table listing which fungicides are labeled for white mold and their efficacy ratings.  These ratings are based on replicated research data collected from University trials.


Management

Several products have been rated as 'good' for white mold management, including Aproach, Endura, and Proline.  If using fungicides for white mold management, keep in mind that efficacy may be based on the ability of the fungicide to penetrate into the canopy, and the timing of the fungicide application. Fungicides will be most effective at reducing the impact of white mold when applied at or close to growth stage R1. 

However, Wisconsin research data indicates that fungicides applied up to growth stage R3 (early pod - pods are 3/16-inch long at one of the four uppermost nodes) may have some effect on white mold severity, but later applications will likely not be as effective at reducing disease. Once symptoms of white mold are evident, fungicides will have no effect on reducing the disease.  Fungicide applications for white mold management may be most useful on fields where varieties rated as susceptible to white mold are planted in a field with a history of the disease.

Harvest
If a soybean field is diagnosed with high levels of white mold, this field should be harvested last.  This will help reduce the movement of the survival structures of the white mold fungus by harvesting equipment, to fields that are not infested.  Also, be sure to clean all harvesting equipment thoroughly at the end of the season to avoid inadvertent infestation of fields.  Rotations of 2-3 years between soybean crops can help reduce the level of the fungus causing white mold in fields. 

Until Next Time,

 

Sean D. Jordal

Agronomist

ProHarvest Seeds

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