Problems with off-target movement of products with the chemical dicamba

by: Julienne Irihose, University of Nebraska-Lincoln, Junior Integrated Science Major

This blog is part of The Science Behind Dicamba Series from Dr. Andrea Basche’s course.


“I’ve never seen anything even close to this,” says Larry Steckel, a weed specialist at the University of Tennessee. “We have drift issues every year in a handful of fields, but I’ve never seen anything like this.” In October of 2017, a final report from Integrated Pest Management at the University of Missouri stated that about 3.6 million acres of soybeans were injured by off- target movement of dicamba around the U.S.  In 2017, the Nebraska Department of Agriculture received over 90 dicamba-related complaints of dicamba drifting into neighboring fields with about 60,000 acres affected by dicamba.

Soybean is an important crop in the United States and Nebraska as well. A Soybean seed or sometimes called “bean” is composed of 80% meal and 20% oil. When processed the meal is used to feed poultry, livestock and also used as a source of protein. The oil is used as a vegetable oil, an ingredient for margarine, and industrial uses such as paints and also used for biofuel. Economically, soybean is also important: it is the second largest harvested crop in Nebraska and the state ranks the fifth in the United States in its production. Nebraska exports 50% of its harvested soybeans and the U.S exports 62% of soybeans produced in the country.

Dicamba is a weed killer that was used for decades in corn production. This herbicide and others in its group were identified to control broadleaf weeds in grass crops which meant it could damage not only weeds, but also crops with broadleaves like soybeans and cotton. Dicamba came with some problems of sensitivity and volatility. Dicamba is a very highly active chemical that if used 0.005% more than what was supposed to be applied could cause damages to crops. Another factor that cause dicamba to have high risks of off- target movement is the high level of volatility meaning this chemical has the ability to turn from the liquid state to the gaseous state and escapes away. This ability increases more under high temperature which could explain what happened the summer of 2017 as mentioned above.

I have mentioned how dicamba damaged tons of acres of soybeans in 2017, but why did damages increase so dramatically last year if dicamba was around for a long time? Dicamba was used before in corns because it could harm broadleaves crops like soybeans or cotton. In 2017, the biotech company Monsanto released Dicamba Tolerant soybean (DT soybeans) for commercial use. The new technology dicamba-tolerant (DT) soybeans (Roundup-Ready 2 Xtend) were soybeans that could resist the damage of dicamba.  Remember that dicamba is volatile and so active. In case it was sprayed and moved to non-tolerant soybeans and other broadleaves, damages could be done.

After the damages caused by dicamba to non dicamba tolerant soybeans and other sensitive plants, in 2018 the United States Environmental Protection Agency (EPA) classified the three product labels (XtendiMax®, FeXapan®, and Engenia®)  for Dicamba as Restricted Use Pesticides (RUPs). A restricted use herbicide means that for farmers to use the herbicide they will have to be certified, licensed applicators and take trainings before applications. Anyone who will be handling an opened or partially used containers of dicamba while mixing or loading must have the trainings. For the growing season of 2018, the EPA has also required the three companies (DuPont, BASF and Monsanto) producing dicamba products to make changes on the labels. Some of the changes included a reduced maximum wind speed and limited times of application during the day. In implementing these new rules, the Nebraska Department of Agriculture (NDA) has required these three companies to make sure the buyers of their products take the University of Nebraska Lincoln trainings before selling them the products.

Figure 3 Engenia herbicide

Figure 3 Engenia herbicide Retrieved from http://news.agropages.com/News/NewsDetail—24472.htm

Different states have many more restrictions on this new technology and farmers who used the technology last year think it is not right to stop the technology since it was beneficial against the issue of weeds that are resistant to other herbicides. However, dicamba may not be a long-term solution to this problem. So the next question will be how to delay the resistance of weeds to dicamba?

If you need more information about the issue of dicamba in Nebraska or need to ask a question, please check the Nebraska Department of Agriculture website at http://www.nda.nebraska.gov/ or the University of Nebraska Extension at https://extension.unl.edu/.

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