Pesticides

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

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:

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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.

Field Observations Thru July 21

Corn

Corn growth varies greatly throughout the county, but, more fields are beginning to tassel.  As corn begins to tassel, nutrient (K > N > P) and water (0.30 inch per day) demands for the crop are close to maximum. Heat and drought will affect potential number of kernels.  Scout for insects (e.g., corn leaf aphid, western bean cutworm, corn earworm, fall armyworm) and diseases (e.g., gray leaf spot, southern rust, northern leaf
blight). Total leaf defoliation severely affects final yields.

VT (Tasseling) – Stage VT occurs two to three days before silking, when the last branch of the tassel is completely visible but silks have not emerged yet from the ear shoot. The plant has reached full height and the pollen shed begins. The time between VT and R1 can vary with different hybrids and due to environmental conditions.
Pollen shed (pollen drop) normally occurs during the late morning or early evening. Hail damage is more serious at this time than for any other growth period. All leaves have emerged and the complete loss of a pollen source would result in no grain formation.

We are nearing a point in the growing season where it is time to scout your corn fields and make a decision regarding fungicide applications. Click here to view the 2023 corn fungicide ratings.

Soybeans

Postemergence herbicide applications – Don’t forget the preharvest intervals (PHI) for grazing or harvest. Read more here.

 

Soybean Postemergence Weed Control – Grasses

Soybean Postemergence Weed Control – Broadleaves

Soybean Growth & Development – R2: Full Bloom

  • Open flower at one of two uppermost main-stem nodes
  • About 50% of the total mature node number has been established.
  • Very rapid nitrogen (N), phosphorus (P), potassium (K) and dry-matter accumulation is occurring and will continue through R6.
  • Defoliation of the plant of 50% at this stage will reduce yield by 6%.
  • Approximately 60 days away from beginning of physiological maturity (R7).

County Rainfall Update

Mount Vernon, OH

Corn Water Requirements

Soybean Water Requirements

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.

Soybean Postemergence Weed Control – Broadleaves

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 16 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

Why are my soybeans yellow? Part 1

Soybeans throughout the county just don’t look good right now.  Development has been slowed and many fields have areas (sometimes large areas) with a light green or yellowish tint to the beans.  What is causing this yellowing? One possibility is:

Yellow Flash (glyphosate)

Temporary yellowing of newly emerged soybean leaves due to glyphosate application to glyphosate-resistant beans. More common in:

  • Conditions conducive to rapid soybean growth (high temperatures and/or humidity)

  • High rates/areas of overlap
  • Areas with micronutrient deficiency

Injury often appears one to two weeks after application and often disappears by 21 days after the area was treated. There is no evidence of yield loss from this phenomenon.

Click here for more information on Yellow Flash.