Pesticides

Soybean Postemergence Weed Control – Grasses

After planting, the second biggest challenge we face is timely weed control.  If you haven’t already made a postemergence application, it might be time to check your fields.  Most beans (and weeds) are at stage that might warrant an application.

Table 15 below from the 2023 OSU Weed Control Guide compares the relative effectiveness of herbicides on individual weeds. Ratings indicate the level of control of weeds present at the time of application, and are based on labeled rate and weed size or growth stage.

Click on table to enlarge

Dicamba Deadline Reminder

Source: Dr. Alyssa Essman

Crop progress is highly variable this year. Some early planted crops have emerged and have had decent growth following recent rains. Dry weather has delayed the emergence of some later planted crops. This means there will also be variability in growth stages, which can have implications for POST application timings. The deadline to apply dicamba over-the-top (OTT) in Ohio is coming soon. For OTT applications of the dicamba products labeled for this use, the cutoff is up to and through June 30th, or the labeled growth stage. Below are the cutoff dates and/or soybean growth stages for the different products.

  • XtendiMax – R1 growth stage or through June 30th, whichever comes first.
  • Engenia – no later than June 30th
  • Tavium – V4 growth stage or through June 30th, whichever comes first.

A soybean plant is at the V4 growth stage when there are four open trifoliates. The R1 growth stage occurs when there is one open flower somewhere on the main stem. See here for detailed descriptions and pictures of soybean growth stages. Table 8 and table 18 of the weed control guide have information related to the maximum crop size and harvest intervals for POST applications in corn and soybean, respectively. As always, it’s important to scout fields before planning applications and follow the herbicide label guidelines.

Weed Response to Postemergence Herbicides in Small Grains

When determining your herbicide program for spring applications, the stage of the wheat crop should be considered.  The majority of wheat herbicides labeled for application at certain wheat growth stages have very short windows in which they can be applied.  The popular broadleaf weed herbicides 2,4-D and MCPA are efficient and economical, but can only be applied for a short period of time between tillering and prior to jointing in the early spring.  Wheat growth stages and herbicide timing restriction are outlined in a in a post last week (Herbicide Applications on Winter Wheat).

Another consideration you should take into account when planning a spring herbicide application is the plant back (or recrop) restrictions to double crop soybeans.  Many of the herbicides listed in Table 19,  have soybean plant back restrictions greater than the typical three month time period between spring applications and double crop soybean planting.  The soybean plant back restrictions greatly reduce the number of options available to wheat producers who double crop soybeans after wheat.

Herbicide Applications on Winter Wheat

When determining your herbicide program for spring applications, the stage of the wheat crop should be considered.  The majority of wheat herbicides are labeled for application at certain wheat growth stages and some commonly used herbicides have very short windows in which they can be applied.  The popular broadleaf weed herbicides 2,4-D and MCPA are efficient and economical, but can only be applied for a short period of time between tillering and prior to jointing in the early spring.  Wheat growth stages and herbicide timing restriction are outlined in Figure 1.

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.

Ohio Department of Agriculture Reminds Pesticide Applicators of June 30 Cutoff Date for Dicamba Products

The Ohio Department of Agriculture (ODA) is reminding pesticide applicators of the June 30 cutoff date for over-the-top dicamba products to soybeans. No additional applications can be made to this year’s crop after this date, regardless of growth stage.

Dicamba is an herbicide used to help limit unwanted weeds around crops. In 2018, the Environmental Protection Agency (EPA) designated new dicamba products as restricted use, meaning they can only be used by certified applicators.

In December 2021, the EPA released its 2021 incident report, which indicated that across the United States “more than 1 million acres of non-dicamba-tolerant soybean crops were allegedly damaged by off-target movement of dicamba.” In Ohio, there were 34 reported incidents involving dicamba.

If you have questions or concerns about dicamba please contact the Division of Plant Health’s Pesticide & Fertilizer Regulation Program at (614) 728-6987 or Pesticides@agri.ohio.gov.

Rainfast Intervals, Spray Additives, and Crop Size for Postemergence Soybean Herbicides

Mother nature is finally cooperating, allowing us to get some corn and beans in the ground.  Later this summer it will be time for postemergence herbicide applications.  The table below from the “2022 Weed Control Guide” lists important information on rainfast intervals, spray additives and crop size  for soybean postemergence applications.Click on the table to print a camera ready copy

 

Why Should You Calibrate Your Sprayer Even If it has a Rate Controller?

by: Erdal Ozkan, OSU

Whenever I give a presentation about the need to calibrate a sprayer and how to do it, there is always someone asking me this same question: “I have a rate controller in the cab that regulates the flow rate of the sprayer regardless of the changes in sprayer ground speed. I just enter the gallons per acre application rate, and the controller does the rest, just like a cruise control in a car. So, should I still calibrate the sprayer? The answer is, Yes, a calibration should be done. Although the rate controllers do an excellent job with regulating the flow rate of nozzles to keep the application rate constant regardless of the changes in travel speed, a manual calibration at least once a year is needed for two reasons: 1) to ensure the rate controller is functioning properly, 2) the rate controller is not forced to operate outside the pressure operating range for the nozzles on the sprayer boom. Let me elaborate on both points I made and share with you the reasons why a manual calibration of a sprayer is a good idea. Continue reading →

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.

Continue reading →