June 4, 2018
YEAR TWO OF DICAMBA USE IN SOYBEANS
The herbicide dicamba was approved for widespread use on soybeans for the first time ever in 2017, provided that the soybeans were the new dicamba-tolerant (DT) varieties. Dicamba is a selective post-emergence herbicide that can be very effective manage tough to control broadleaf weeds such as waterhemp, ragweed, and horseweed. Dicamba is also effective in controlling palmer amaranth, which has been a new weed challenge in Minnesota, but has been a serious hard-to-control weed problem in other areas of the United States. Unfortunately, dicamba also has the potential to damage non-tolerant soybeans, as well as other sensitive crops and plants, near the dicamba treatment areas.
The chemical technology behind dicamba is not new. It has been around for decades, sold as the herbicide Banvel under several labels, for use on corn, sorghum, small grains, and pastures. It has always been a very effective herbicide to control difficult perennial broadleaf weeds. Over the years, there have been problems associated the use of Banvel herbicide, as far as drift injury to soybeans and other sensitive crops. One difference between the use of Banvel herbicide on corn and small grains, compared to the newer dicamba-based herbicides for DT soybeans, is that they were typically applied much earlier in the growing season, when injury impacts to other crops and plants were reduced.
There are currently three dicamba-based products registered by the Environmental Protection Agency (EPA) for use in DT soybeans in the U.S. The products are: “XtendiMaxTM with VaporGripTM Technology”, sold by Monsanto, “EngeniaTM”, sold by BASF, and “FeXapanTM with VaporGripTM Technology”, sold by DowDuPont. These products were approved by the EPA on a conditional basis for use on dicamba-tolerant (DT) soybeans for the 2017 and 2018 crop years. Following the 2018 crop year, EPA will evaluate the continuation of the herbicide labels of the three products for future years.
Dicamba is a highly volatile chemical that can drift or volatilize quite easily, especially under certain environmental conditions. In 2017, EPA received more than 2,700 crop injury claims, affecting over 3.6 million acres, related to the use of the new dicamba-based herbicides on DT soybeans. This included hundreds dicamba injury claims in Minnesota and other Midwestern States, as well as many more dicamba damage situations that were never reported to EPA or State Agriculture Departments. The total extent of the dicamba-related injury to crops and other sensitive plants in 2017 has not been quantified by EPA. However, the seriousness of the injury was many times related to the timing of the herbicide application and the weather conditions when the dicamba was applied.
In response to the dicamba-related injury concerns injury concerns in 2017, EPA consulted State Departments of Agriculture and Extension Services at Land-Grant Universities to review the causes of the dicamba injury and potential solutions. Following that review, EPA issued the following Federal label requirements and restrictions for the use of the dicamba-based products in 2018:
- The new dicamba-based products for soybeans are classified as “Restricted-Use” pesticides.
- Training is required to purchase or apply the newer dicamba-based products.
- Applicators are required to keep herbicide application records specified by the Federal label.
- Applications may only be made between sunrise and sunset.
- Application is restricted to conditions with wind speeds between 3 mph and 10 mph.
- Applications can not be made when the wind is blowing toward a sensitive crop.
- Application can not be made when rain is predicted in the 24-hour forecast.
- Spray tanks must be cleaned out in a manner that prevents cross-contamination.
- Application should end when soybeans reach the R2 stage of development.
In addition, many States, including Minnesota, have added additional restrictions for 2018 on the application of the dicamba-based products for DT soybeans in their States. In Minnesota, the dicamba-based herbicides can not be applied to soybeans after June 20, 2018, or if the daily temperature is 85 degrees Fahrenheit or higher, or is forecast to be above that level at anytime for that day. More details on the Minnesota requirements are available on the Minnesota Department of Agriculture website at: http://www.mda.state.mn.us/chemicals/pesticides/dicamba/dicambafaq.aspx.
To find specific restrictions for the new dicamba-based herbicides in other States, it is recommended to go to websites for the various State Departments of Agriculture.
The June 20 date was chosen based on the normal stage of development for most soybeans in Minnesota by certain dates, and the susceptibility to injury by non-DT soybeans. Regarding the temperature requirement …… if the temperature is 75 degrees F at sunrise, but is projected to exceed 85 degrees F later in the day, application of the dicamba-based herbicides is not permitted. However, if the 85-degree forecast is for the following day, the herbicide could be applied, provided that the other application criteria have been met.
The combination of the new Federal and State restrictions for the application of the newer dicamba-based herbicides on DT soybeans make it like “threading a needle” to find days before June 20 when weather conditions meet requirements for application. The combination of wind speed and direction, together with temperature and rainfall restrictions could very much limit the number of application days. In 2018, there have already been numerous days in late May and early June, that have either exceeded 85 degrees F, been windy, or received rainfall. The late planting season for soybeans in parts of southern Minnesota and northern Iowa could also create some issues for timely application of the dicamba-based herbicides on DT soybeans this year.
Continued availability of the dicamba-based herbicides for DT soybeans may be critical in the future for the control of waterhemp, ragweed, palmer amaranth, and other difficult to control broadleaf weeds, some of which are becoming resistant to other herbicide options. Having future availability of the dicamba-based products for DT soybeans will likely rely on farm operators themselves, and their ability to follow label directions and good management practices when using these herbicides.
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Note — For additional information contact Kent Thiesse, Farm Management Analyst and Senior
Vice President, MinnStar Bank, Lake Crystal, MN. (Phone — (507) 381-7960);
E-mail — kent.thiesse@minnstarbank.com)