The Cost of Herbicide Resistance

An often overlooked impact of herbicide resistance has been the increase in amount of money spent by soybean producers for herbicides in today’s production environment compared to the days prior to the significant presence of glyphosate-resistant (GR) weeds.

To drive this point home, I have compiled a table that shows 1) estimated seed and weed control costs for soybean production in a year (1990) prior to GR varieties, 2) estimated seed and weed control costs for soybean production in a year (2008) during the time of GR varieties and glyphosate as the sole herbicide, and 3) estimated seed and weed control costs for soybean production in a system (2018) designed to manage herbicide-resistant (HR) weeds.

The significant occurrence of GR weeds starting early in the second decade of the 21^st century forced growers to abandon the glyphosate-only weed control program that had been used since the introduction of GR varieties in the mid-1990's. However, producers still plant RR varieties during this post-GR weeds period since glyphosate application remains as a component of most weed control programs.

The data in Table 1 below are taken from annual Soybean Enterprise Budgets compiled by personnel in MSU’s Dept. of Agric. Economics (click linked year for that year’s budgets). The example data are for furrow-irrigated soybeans grown in 20- or 30-in.-wide rows on clay soils in the Delta area of Mississippi. 1990 data (conventional, non-GR soybean varieties) are from Tables 14 A-D of the 1990 Planning Budgets, 2008 data (total glyphosate weed control system; i.e., GR varieties and glyphosate herbicide) are from Tables 2 A-D of the 2008 Planning Budgets, and 2018 data (weed control system for managing HR weeds) are from Tables 2 A-D of the 2018 Planning Budgets.
 

Using the Bureau of Labor Statistics Inflation calculator, the figures in Table 2 show estimated weed control costs and seed + weed control costs for the three shown years adjusted for inflation over the Jan. 1990 to Oct. 2017 period.

Using the data in the above tables, the following summary points are presented.

•   It is likely that the above budget estimates do not/will not match that of any one producer. However, they are reasonable estimates of the costs associated with soybean weed control in the shown years.

•   The introduction and use of HR soybean varieties has resulted in dramatic increases in the cost of soybean seed (compare 1990 and 2018 figures in Table 1 above).

•   The total glyphosate weed control system–i.e., GR soybean varieties and glyphosate herbicide (2008 budget above)–was by far the cheapest weed control system for soybeans. However, the development of HR weeds has now rendered this weed control system ineffective.

•   Because of the development of HR weeds, and in particular GR weeds, a much more expensive weed control system (2018 budget above) must now be used in an attempt to manage HR weeds that are now present and to prevent their further development. In fact, the estimated 2018 budget for soybean seed + weed control is an estimated $85/acre more than the inflation-adjusted cost prior to GR soybeans (1990 budget).

•   Weed resistance to herbicides is not going away. In fact, ignoring this now and in the future will result in even more weed management problems that even increasing herbicide mode-of-action diversity and weed control expenditures will not solve.

•   There are no new herbicides with novel modes of action in the foreseeable future. Thus, the expense for weed control shown in the 2018 planning budget above may be altered somewhat, but should not be to a great degree if producers are serious about managing for present and potential HR weeds.

The figures and summary points above show that managing weeds in soybeans is not only an agronomic problem, but a financial problem as well. Regrettably, this is not likely to change if soybean producers desire to keep weeds at bay.

Composed by Larry G. Heatherly, Nov. 2017, larryheatherly@bellsouth.net. My thanks to Gail Gillis, Senior Extension Associate in the MSU Dept. of Agric. Economics, for providing archived data.