Waterhemp and weeds wilting in soybean field after dicamba application.

2022-23 Rapid Ag: Improved Prediction of the Atmospheric Transport and Fate of Dicamba - RENEWAL

February 22, 2021

Project Leader

Tim Griffis, Department of Soil, Water, and Climate

Team Members

  • John Baker, USDA-ARS and Department of Soil, Water, and Climate
  • Debalin Sarangi, Department of Agronomy and Plant Genetics
  • Pam Rice USDA-ARS and Department of Soil, Water, and Climate
  • Jeffrey Gunsolus, Department of Agronomy and Plant Genetics
  • Alexander Frie Department of Soil, Water, and Climate

Non-Technical Summary

A new dicamba herbicide has been used to control weeds in Minnesota soybean crops. Its application in Minnesota has ranged from 586,000 lbs in 2017 to over 700,000 lbs in 2019. Unfortunately, drift and volatilization of dicamba has resulted in substantial offsite damage to non-target crops (~276,000 acres). This vexing problem has raised serious environmental concerns in Minnesota and the US Corn Belt. 

Objectives and Goals

The goals of this project, therefore, are to:

  1. Quantify dicamba losses and offsite transport from soybean fields
  2. Examine how meteorology and environmental conditions influence dicamba losses and offsite crop damage
  3. Provide best management practices for dicamba application in Minnesota
  4. Develop a dicamba transport calculator to make informed decisions based on environmental conditions
  5. Provide a state-of-science report to the MDA regarding dicamba transport and fate in Minnesota

Justification

This proposal seeks support for a second phase of research focused on predicting the transport and fate of the herbicide dicamba (i.e. Xtendimax, a soybean product). A 1-page summary of previous work is enclosed and a presentation can be viewed at https://www.biometeorology.umn.edu/links/dicamba-summary.

Dicamba has long been used to control broadleaf weeds in agricultural systems [Behrens and Lueschen, 1979], but drift (i.e. offsite transport during application), volatilization (i.e. evaporation after application), downwind transport, and damage to non-target crops continues to raise serious concerns [Riter et al. 2020]. In recent decades, its use had been limited in favor of less volatile, broad spectrum, herbicides such as glyphosate. However, there has been renewed interest in applying dicamba due to increased herbicide resistance and resulting weed pressure. Recently, dicamba use has risen due to new formulations with significantly lower volatility, development of dicamba resistant crops, and approval of a new dicamba formulation by the United States Environmental Protection Agency (EPA). In Minnesota, soybean dicamba product usage increased from ~586,000 lbs in 2017 to >700,000 lbs in 2019. However, its application in Minnesota from 2017 to 2020 resulted in ~276,000 acres of offsite crop damage [Minnesota Department of Agriculture]. Dicamba crop damage is well documented, however, the factors influencing the transport and extent of offsite effects are poorly constrained because atmospheric observations remain relatively rare.

Since 2017, the dicamba problem has evolved rapidly. Regulations regarding application (i.e. application calendar cutoff date, air temperature thresholds, air temperature inversion awareness) have changed and chemical companies have altered the formulation and developed add-on products (i.e. Astonish) to reduce drift and volatilization. There remains considerable concern and debate regarding dicamba’s drift potential, volatility, atmospheric loading, and subsequent transport to non-target fields and natural ecosystems [Jones et al. 2019; Riter et al. 2020; Soltani et al. 2020].

Our previous experiments detected dicamba (i.e. Xtendimax, formulation 3,6-dichloro-o-anisic acid) damage to offsite non-traited soybeans more than 50 m (164 feet) from the application field—well beyond the required label buffer of 110 feet (label requirements are increasing the buffer for 2021). In addition, our atmospheric modeling, constrained by emission estimates, found that dicamba may be transported 100’s of meters under stable atmospheric conditions. Long-term (20 site-years) analyses of atmospheric stability, wind speed, and surface temperature above crop surfaces at UMORE park (Rosemount, Minnesota) indicate that there is a very limited window of time when it is safe (i.e. meets label requirements) to apply dicamba. For instance, stable atmospheric conditions persist over much of the growing season from about 7 pm to 8 am and mean daytime wind speeds approach 10 mph (i.e. label cutoff requirement) from mid to late afternoon during spring. Further, dicamba is suspected to accumulate in the atmosphere during warm stable nights. This may adversely impact crops kilometers from the application site via air mass movement [Bish et al. 2019; Mueller and Steckel, 2019]. This nighttime atmospheric loading phenomenon is a serious concern for crop, environment, and human health, but there are scant data to probe the mechanisms.

References

  1. Behrens R and WE Lueschen, (1979) Dicamba volatility, Weed Science, 27: 486-493
  2. Bish MD, Farrell ST, Lerch RN, and Bradley KW (2019) Dicamba losses to air after applications to soybean under stable and nonstable atmospheric conditions. J Env Qual 48:1675–1682
  3. Flesch T, Prueger JH, Hatfield JL (2002) Turbulent Schmidt number from a tracer experiment. Agricultural and Forest Meteorology, 111:299-307.
  4. Flesch T and J Wilson (2005) Estimating tracer emissions with a backward Lagrangian stochastic technique, Micrometeorlogy in Agricultural Systems, Agronomy Monograph no 47, 513-531
  5. Griffis TJ et al., (2017), Nitrous oxide emissions are enhanced in a warmer and wetter world, Proceedings of the National Academy of Sciences of the United States of America, 114: 12081-12085
  6. Hu C, Griffis TJ et al., (2020) Modeling the sources and transport processes during extreme ammonia episodes in the US Corn Belt, Journal of Geophysical Research-Atmospheres, 125, e2019JD031207
  7. Jones GT, Norsworthy JK, Barber T, Gbur E, Kruger GR (2019) Off-target movement of DGA and BAPMA dicamba to sensitive soybean. Weed Technol 33:51–65
  8. Mueller TC and Steckel LE (2019) Dicamba volatility in humidomes as affected by temperature and herbicide treatment. Weed Technol 33: 541–546
  9. Riter LS, Sall ED, Pai N, Beachum CE, and Orr TB (2020) Quantifying dicamba volatility under field conditions: Part 1 Metholology,. Journal of Agriculture and Food Chemistry, 68: 2277-2285
  10. Soltani N, Oliveira MC, Alves GS, Werle R, Norsworthy JK, Sprague CL, Young BG, Reynolds DB, Brown A, Sikkema PH(2020) Off-target movement assessment of dicamba in North America. Weed Technol. 34: 318–330