Spraying

Weed Response to “Burndown” Herbicides

In no-till corn and soybean fields, it is essential to apply herbicides with foliar activity before crop emergence to control existing weeds. Depending upon the herbicide approach used in the field for that year, herbicides used to control weeds at planting may include glyphosate or paraquat. Use of herbicide combinations in burndown treatments is justified in most no-till fields, due to the variety of winter annual weeds present. Consider fall herbicide treatments in fields that are heavily infested with such species as chickweed, marestail, dandelion, wild carrot, and poison hemlock.

Click here for Burndown table

Considerations for Soybean Trait Programs in 2025

Herbicide use is likely to increase in complexity in the coming years, due in part to the EPA’s Herbicide Strategy that was finalized and published in August 2024, among other anticipated changes. One thing that has not changed is that the “label is the law”, and off-label herbicide applications come with potential liability and legal implications, along with potential damage to crops and surrounding areas. In most instances, application cutoff dates are imposed due to increased risk of off-target movement or concerns about herbicide residues in the crop when applied after a certain growth stage. Seed suppliers often send letters this time of year reminding growers that they are also legally bound by the terms of the Technology Use Agreement (“TUA”) entered into with the seed supplier. A TUA contains herbicide application restrictions for the seed variety. Growers should familiarize themselves with the TUAs for their seed products and be aware that a TUA also grants the company rights of access to inspect crops and ensure compliance with the herbicide application provisions.

Here are a couple of reminders as we head into the 2025 growing season regarding the application of herbicides POST in the available traited soybean systems.

Enlist

  • Where 2,4-D is applied preplant or preemergence for burndown ahead of planting Enlist soybeans, the application of products that are not labeled for use in the Enlist system must adhere to the labeled plant back interval for the product used.
  • At present, the only 2,4-D products that are labeled for immediate plant back and over-the-top (OTT) application in the Enlist soybean system are Enlist One (2,4-D choline) and Enlist Duo (2,4-D choline + glyphosate).
  • Growers across the state have been receiving “technology use agreement” letters reminding growers of this, and the fact that it is the growers’ responsibility to ensure that only these products are being applied, regardless of who is making the application. In these letters, potential steps were listed in response to not following these parameters. These steps included: investigating reports of misuse, in-person audits during the 2025 growing season, revoking the grower’s access to the trait technology, and reporting violations to the EPA.

Xtend

  • In February 2024, the EPA vacated registration for the three dicamba products labeled for OTT applications in soybean (Xtendimax, Bayer; Engenia, BASF; and Tavium, Syngenta).
  • Shortly after, the EPA issued an existing stocks order for use of these products for the 2024 growing season. The last date for application of these products in Ohio was June 30th, 2024.
  • At present, there are no options for OTT application of dicamba for growers using Xtend or XtendFlex soybeans for the 2025 growing season. Postemergence control of broadleaf weeds is limited to glyphosate and glufosinate in the XtendFlex system. PPO inhibitors (fomesafen, etc.) can be used POST in any soybean system.

Liberty

  • Soybean yields generally benefit from earlier planting dates, and growers in the region have been planting earlier than the historical norm for the state. Depending on the date of planting, this can have implications for time to soybean emergence and maturity and in some cases can lead to earlier soybean flowering dates.
  • As a reminder, glufosinate can be applied to glufosinate-resistant soybeans from emergence up to soybean bloom (R1).

Using Drones for Spray Application – Adoption Trends in US and Worldwide

Traditionally, aerial pesticide spraying worldwide has been done using conventional fixed-wing aircraft or helicopters with a pilot onboard. However, this is changing fast. Small, remotely piloted aircraft are being used to apply pesticides around the world, especially in East Asia (mainly China, Japan, and South Korea). For example, about 2,800 unmanned helicopters were registered as of March 2016 in Japan, spraying more than a third of the country’s rice fields. Although rice is the main crop treated with spray drones in Japan, use of drones to treat other crops such as wheat, oats, soybean, and other crops has been steadily increasing. According to one report, 30% of pesticide spraying in South Korea is done using drones.

Continue reading Using Drones for Spray Application – Adoption Trends in US and Worldwide →

Suspected 2,4-D Resistant Waterhemp Population Discovered

Source:  ICM News, Iowa State University

We know the evolution of resistance in waterhemp populations happens faster than new herbicides are discovered, so the recent report of dicamba resistant waterhemp in Iowa by Bayer was not unexpected. Corteva has now reported the discovery of a suspected 2,4-D resistant waterhemp population in Iowa. These reports emphasize the need to use herbicides wisely and diversify weed management tactics beyond herbicides, especially as more farmers rely on herbicide group (HG) 4-based postemergence weed control in both corn and soybean.

The particulars

In late January 2024, Corteva reported the discovery of a suspected 2,4-D resistant waterhemp population in 2022 in Wright County, Iowa. A Corteva employee collected two samples of waterhemp seed, one from plants in the field and one from plants growing in the ditch adjacent to the field. While greenhouse testing with seed collected from plants in the field did not confirm resistance, plants grown from the ditch population are suspected to be 2,4-D resistant. The communication reported that the ditch had a multi-year history of 2,4-D application to manage broadleaf weeds. Corteva will continue evaluation of the populations in the greenhouse and the field. If resistance is confirmed in this population, it will become at least the fourth report of 2,4-D resistance in waterhemp, joining prior reports from Nebraska in 2009 (Bernards et al. 2012), Illinois in 2016 (Evans et al. 2019), and Missouri in 2018 (Shergill et al. 2018).

Iowa State University screened populations of waterhemp against several herbicides in 2019 at their 1X rates (Table 1). On average, waterhemp exhibited 17% survival to 2,4-D, 5% survival to dicamba, and 4% survival to glufosinate (Hamberg et al. 2023). We are rapidly losing herbicide options for postemergence control of waterhemp.

Best management practices to slow resistance development

Now is the time to evaluate how to improve weed management in fields. While herbicides will remain the primary tactic to manage weeds, farmers can implement several best management practices to slow herbicide resistance evolution and improve control of weeds like waterhemp.

  1. Choose an effective herbicide program for the weed spectrum present on a field-by-field basis.
    1. Use full rates of effective residual herbicides and plant into a weed-free seedbed.
    2. Include overlapping residual herbicides and multiple effective herbicide groups in postemergence applications to provide longer waterhemp control. Consult manufacturers for specific tank-mix recommendations.
    3. Make timely applications and choose appropriate adjuvants, nozzles, application volume, etc.
    4. Scout fields 7-10 days after postemergence herbicide applications to evaluate weed control.
  2. Use a diversity of weed management tactics, including chemical, mechanical, and cultural options. Narrow row spacing, cover crops, more diverse crop rotations, and tillage are effective tactics to suppress waterhemp.
  3. Control weed escapes prior to seed production to reduce future weed populations and prevent resistance from spreading.
  4. Reduce influx of weed seed into crop fields by managing weeds in field edges and cleaning equipment between movement from problematic fields to clean fields. The detection reported here indicates the threat of weeds in field edges.

EPA issues “existing stocks” order for over-the-top dicamba use

By:Peggy Kirk Hall, Attorney and Director, Agricultural & Resource Law Program

A federal court decision last week vacated the registrations of dicamba products XtendiMax, Engenia, and Tavium for over-the-top applications on soybean and cotton crops, making the use of the products unlawful (see our February 12, 2024 blog post).  The decision raised immediate questions about whether the U.S. EPA would exercise its authority to allow producers and retailers to use “existing stocks” of dicamba products they had already purchased.  Yesterday, the U.S. EPA answered those questions by issuing an Existing Stocks Order that allows the sale and use of existing stocks of the products that were packaged, labeled, and released for shipment prior to the federal court decision on February 6, 2024.  For Ohio, the EPA’s order allows the sale and distribution of existing stocks until May 31, 2024 and the use of existing stocks until June 30, 2024.

Here is the EPA’s order:

  1. Pursuant to FIFRA Section 6(a)(1), EPA hereby issues an existing stocks order for XtendiMax® with VaporGrip® Technology (EPA Reg. No. 264-1210), Engenia® Herbicide (EPA Reg. No. 7969-472), and A21472 Plus VaporGrip® Technology (Tavium® Plus VaporGrip® Technology) (EPA Reg. No. 100-1623). This order will remain in effect unless or until subsequent action is taken. The issuance of this order did not follow a public hearing. This is a final agency action, judicially reviewable under FIFRA § 16(a) (7 U.S.C. §136n). Any sale, distribution, or use of existing stocks of these products inconsistent with this order is prohibited.
  2. Existing Stocks. For purposes of this order, “existing stocks” means those stocks of previously registered pesticide products that are currently in the United States and were packaged, labeled, and released for shipment prior to February 6, 2024 (the effective date of the District of Arizona’s vacatur of the dicamba registrations). Pursuant to FIFRA section 6(a)(1), this order includes the following existing stocks provisions:

Continue reading EPA issues “existing stocks” order for over-the-top dicamba use →

Fall-applied Herbicide Considerations

Now that harvest is finally winding down, our thoughts change to fall weed control.   This is the best time of year to control winter annuals and some of the more difficult to manage overwintering weed species. Biennial and perennial plants are now sending nutrients down to the root systems in preparation for winter. Systemic herbicides like glyphosate and 2,4-D applied at this time will be translocated down into the roots more effectively than if applied in spring when nutrients are moving upward. This results in better control. In addition, the increasingly unpredictable spring weather patterns we have experienced in recent years can influence the timing and efficacy of spring burndown applications. Fall-applied herbicides can lead to weed free situations going into spring until early emerging annuals begin to appear in April, and are an essential component in the control of marestail and other overwintering species.

Here are some reminders when it comes to fall-applied herbicides:

  • Evaluate weed emergence and growth post-harvest to help determine if an application is necessary.
  • Fall-applied herbicides should primarily target weeds that are emerged at the time of application.
  • Species present in large quantities late-season that would necessitate the application of an herbicide include (but are not limited to): marestail, dandelion, wild carrot, poison hemlock, common chickweed, purple deadnettle, henbit, annual bluegrass, and cressleaf groundsel.
  • OSU research has not found much of a benefit from adding metribuzin or other residual products late in the fall. The exception to this is chlorimuron, which can persist into the spring. The recommendation here has generally been to keep costs low in the fall and save those products for spring when you will get more bang for your buck.
  • Herbicides generally work across a range of conditions, though activity can be slower as temperatures drop. Foliar products are most effective when daytime temperatures are in the 50s or higher and nighttime temperatures remain above 40.

Table 1 in the Weed Control Guide for Ohio, Indiana, Illinois, and Missouri provides ratings for various overwintering weed species in response to fall-applied herbicides.

Preharvest Intervals for Soybean Herbicides Applied Postemergence

Preharvest intervals indicate the amount of time that must elapse between the herbicide application and crop harvest. Failure to observe the preharvest interval may result in herbicide residue levels in the harvested portion of the crop in excess of established limits. Also, livestock grazing or foraging treated soybean is not allowed on the labels of many postemergence soybean herbicides. Table 1 contains information regarding preharvest intervals and grazing restrictions for a number of postemergence soybean herbicides.

Table 18 from the OSU Weed Control Guide shows the PHI and feeding restrictions for postemergence soybean herbicide applications.

Wheat Growth and Development – Feekes 10.2 – 10.5

Today managing your wheat crop requires knowledge of the different growth stages of the plant.  Growth stage identification is critical for scouting and proper timing of fertilizer and pesticide applications.  Each week throughout the rest of the growing season I will discuss the various wheat growth stages I am seeing in our wheat fields and management issues at each stage.  Today I will focus on the heading stages Feekes 10.2 through Feekes 10.5 .

FEEKES 10.1-10.5 – HEADING 

Figure 1. Wheat flag leaf, ligule, awns and head at Feekes 10.5.

 

Heading marks the emergence of the wheat head from the leaf sheath of the flag leaf, and is subdivided into stages based on how much of the head has emerged.

Stage 10.5 is shown in Figure 1.

 

 

 

  • 10.1    Awns visible, head beginning to emerge through slit of flag leaf sheath.
  • 10.2    Heading one-quarter complete.
  • 10.3    Heading one-half complete.
  • 10.4    Heading three-quarters complete.
  • 10.5    Heading complete.

If you need a reminder on how to determine the different heading growth stages, watch this video.

Management.

Scout for insects, weeds, and diseases. A fungicide application may be considered to protect heads from scab.

Check fungicide label for pre harvest interval restrictions and proper growth stage for application.

Click here to go to an earlier post containing the 2023 Wheat Fungicide Ratings. 

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.