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.

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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

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:

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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.

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.

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