Double-Crop Soybean Weed Management

by: Dr. Mark Loux, OSU Extension

It’s been a tough summer in parts of Ohio to do anything on a timely schedule and there are some weedy fields.  The best advice we have for big weeds in full-season soybeans is to increase rates and the complexity of POST herbicide applications, while still adhering to cutoffs for the application of certain herbicides as much as possible.  Dicamba products, XtendiMax, Engenia, and Tavium, cannot legally be applied to Xtend and XtendiFlex soybeans after June 30.  This cutoff date pertains to use in double-crop soybeans also.  If you are planning on planting Xtend or XtendiFlex soybeans in double-crop fields and using dicamba as a burndown, apply before Friday.  There isn’t a cutoff date for most other POST soybean herbicides – it’s based on either crop stage (eg R1) or days before harvest.

Double crop soybeans usually need some type of weed control program, although how weedy they get depends upon weeds surviving down in the wheat that can take off once they receive light; how much rain we get in July, which drives additional weed emergence and rate of soybean growth; and how fast the soybeans grow and develop a canopy.  Control can occur via the use of pre-plant/preemergence burndown herbicides, followed by POST as needed.  It’s also possible to accomplish this with one early POST application in Enlist soybeans, using Enlist Duo or a combination of Enlist One with glyphosate or glufosinate.  And also in LLGT27 soybeans with a combination of glyphosate and glufosinate.  Herbicides need to address marestail in many fields, which is often lurking in the wheat ready to regrow.  Marestail that are taller and get cut off by the combine will be more difficult to control than the smaller intact ones below the cutter bar.  Herbicide options vary depending upon the weeds and what type of soybeans are planted.  More effective options include:

  • Glyphosate or glufosinate + Sharpen (1 oz) + MSO – any soybean, prior to emergence
  • Glyphosate or glufosinate + 2,4-D – any soybean, at least a week before planting
  • Enlist Duo; glyphosate or glufosinate + Enlist One (Enlist soybeans) – PRE or POST, no wait to plant
  • Glyphosate + XtendiMax or Engenia (Xtend or XtendiFlex soybeans) – PRE, apply by June 30
  • Glyphosate + glufosinate – PRE in any soybean, PRE or POST in LLGT27 soybean

​​​​​​​It is possible to include residual herbicides with a PRE burndown treatment, but their value in this situation is questionable.  Residual herbicides with long recrop intervals to corn should be avoided.  POST options in double-crop include glufosinate, glyphosate, Enlist One/Duo, and conventional herbicides, depending upon the type of soybean planted.  One caution here is to avoid excessive injury to soybeans that slows growth and development since this is likely to reduce yield due to the short season.  Weed emergence is reduced and variable in July compared with May and June.  Where burndown herbicides are used, but there is still a need for POST herbicides to control a flush of late-emerging weeds, consider reduced rates.  Research we conducted back in the 1990s demonstrated that weeds up to 2 inches tall can usually be controlled with half of a typical labeled rate.  When we planted soybeans in early June, the single application of a half-rate provided adequate control, versus early May when a second application was needed.  So this should be a suitable approach for double-crop soybeans.  Just be sure to start with an effective burndown at planting, and apply when weeds are well within the 2-inch size.

Kill Poison Hemlock Now

 

– Christine Gelley, Agriculture and Natural Resources Educator, Noble County OSU Extension

Poison hemlock is a concern in public right of ways, on the farm, and in the landscape!

Poison hemlock has already emerged in a vegetative state around Noble County and beyond. Soon it will be bolting and blooming on stalks 6-10 feet tall. All parts of the plant are toxic to all classes of livestock if consumed and is prevalent along roadsides, ditches, and crop field borders. It is a biennial weed that does not flower in the first year of growth but flowers in the second year. The earlier you can address poison hemlock with mowing and/or herbicide application, the better your control methods will be.

Poison hemlock is related to Queen Anne’s lace, but is much larger and taller, emerges earlier, and has purple spots on the stems. Another relative that is poisonous is wild parsnip, which looks similar to poison hemlock, but has yellow flowers. Giant hogweed is another relative of poison hemlock that is also toxic. All of these plants have umbel shaped clusters of flowers.

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Alternative spring burndown/postemergence strategies when herbicides are in short supply

by: Dr Mark Loux, OSU

There is a lot of speculation about herbicide shortages for the 2022 growing season, and some products are apparently getting more expensive and/or scarce now. This will affect herbicide buying and weed management decisions for the 2022 season. The two main active ingredients that we’re hearing about right now are glyphosate (Roundup, others) and glufosinate (Liberty, others), for which prices have increased substantially. There will likely be limited supplies of other pesticide active ingredients as well, but in the short term, a shortage of these two active ingredients poses some major challenges for corn and soybean production. The purpose of this article is to discuss ways to minimize the impact of herbicide shortages, primarily glyphosate, on corn and soybean production. As you search for alternatives to these two herbicides and others, the weed control guides and technical guides produced by University Extension and industry are an important tool for planning weed management programs and herbicide purchases.

Some guiding principles based on our experience that may help with decisions, especially where glyphosate will not be in all applications:

  1. Spring tillage is an option to replace herbicide burndown. Can cause long-term compaction problems if tilled when too wet. Waiting until weeds are large makes tillage less effective. Weeds that survive tillage will be difficult to control with POST herbicides. In other words, till when soil conditions are fit and before weeds are huge.
  1. Where it’s only possible to use glyphosate once, it may be needed most in the burndown. Saflufenacil can be added for enhanced control of rye and ryegrass, and marestail. ACCase herbicides (e.g. clethodim, quizalifop) can then be used for POST grass control in soybeans. Glufosinate, Enlist Duo, or XtendiMax/Engenia can be used for many broadleaf weeds, especially the glyphosate-resistant ones. Where residual herbicides are omitted, or do not provide enough control, we would expect POST treatments to struggle more in the absence of glyphosate with weeds such as lambsquarters. So use residuals. Glyphosate is still more than just a grass herbicide.

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New Enlist Labels – When Enlist is Outlawed, Only Outlaws……

By: Dr. Mark  Loux, OSU Extension

Sometimes you’d like the s**t to stop hitting the fan just long enough to get cleaned up, but you can’t get a break. Like when you’re in the middle of an endless pandemic, a worldwide shipping fiasco, herbic ide scarcities and price increases, and parts shortages. And just when you had it worked out to use Enlist herbicides on Enlist soybeans for 2022 so you wouldn’t have to deal with dicamba, their use is no longer legal in your county. We’re trying to find something reassuring to say here, but there’s not much.  The USEPA issued a new seven-year registration for Enlist One and Enlist Duo, valid through January 2029.  Changes include a revised application cutoff for soybeans, “through R1” that replaces “up to R2” on previous labels, and the addition of  a slew of spray nozzles to the approved nozzle list.  The most significant change for Ohio is that due to changes in Endangered Species information, Enlist One and Enlist Duo cannot be used in 12 Ohio counties:  Athens, Butler, Fairfield, Guernsey, Hamilton, Hocking, Morgan, Muskingum, Noble, Perry, Vinton, and Washington. We contacted Corteva to see if this was likely to change anytime soon, and got no assurances of this, although the PR information they have distributed indicates it is possible.

This really couldn’t happen at a worse time for growers in these counties. We lack solid information on herbicide availability and price, and it’s a fluid situation, but it appears that glyphosate and glufosinate can be in short supply, and prices high.  Glyphosate resistance in key weed species makes us dependent on POST soybean herbicide systems based on use of glufosinate (Liberty etc), dicamba (XtendiMax/Engenia), or 2,4-D (Enlist One/Duo). The Enlist system allows use of glyphosate, glufosinate, and 2,4-D, and combinations of these.  While Enlist soybeans are tolerant of other 2,4-D products, Enlist One and Duo are the approved 2,4-D products for all POST applications to Enlist soybeans, and any preplant or preemergence applications that occur less than 7 days before planting or anytime after planting.  As far as we know, this prohibition of use does not apply to legal uses of other 2,4-D products.  Some things to consider here:

– Some growers/applicators were planning on omitting glyphosate from burndown and/or POST applications.  In the Enlist system, this increases the overall importance of the 2,4-D in these applications.  Where the Enlist products cannot be used, revaluation of the mixture is warranted.  It may be necessary to use glyphosate, or an alternative 2,4-D product in the burndown (with a 7-day wait to plant), or other herbicides, such as Sharpen or Gramoxone.

– The most obvious replacement for Enlist products in POST applications is glufosinate since glyphosate won’t control most populations of ragweed, waterhemp, or marestail.  Growers going this route should check on availability and price immediately, since supply seems to be finite.  For those in the 12 counties who are unwilling or unable to use glufosinate, the Enlist soybean essentially becomes a RoundupReady soybean with respect to herbicide use.

– Most users of glufosinate supplement the grass control by including either glyphosate, or a POST grass herbicide such as clethodim.  Glufosinate is weak on barnyardgrass and yellow foxtail, volunteer corn, and large grasses in general.

– While spray volume and nozzle type are not that critical for effectiveness of 2,4-D and glyphosate, glufosinate requires these to be optimized to maximize activity.  Most growers tell us that for glufosinate, 20 gpa works better than lower spray volumes.  The nozzles that work well to minimize off-target movement of Enlist products may not be optimum for glufosinate.

– Where 2,4-D cannot be used in the POST, the effectiveness of the residual herbicides used becomes more important.  Glufosinate applied alone or with just a grass herbicide can be less effective on certain broadleaf species, and large weeds in general, compared with mixtures of 2,4-D with glufosinate or glyphosate.  We recommend using residual herbicides at planting, and possibly increasing herbicide rates and the overall complexity of the mixture.

Information we have received from Corteva includes several documents with explanation of label changes and restrictions, and supplemental labels for Enlist One and Enlist Duo.  Aside from this, we don’t know any more than anyone else.

Save the Dates – Central Ohio Agronomy School

Due to COVID uncertainties the 2022 Central Ohio Agronomy School has been pushed to March. 

Monday March 7 – 6:30 – 9:00p.m.

Monday March 14 – 6:30 – 9:00p.m.

Monday March 21 – 6:30 – 9:00p.m.

Monday March 28 – 6:30 – 9:00p.m.

The School will be at the new Ramser 4-H Activity Center (on the fairgrounds)

700 Perimeter Dr.  Mount Vernon, OH  43050

More details to come