Herbicide-resistant weeds (copy)

Marestail plants — Conyza canadensis — have a resistance to glyphosate roundup herbicide. They have survived to infest a crop of harvest-stage wheat. 

In the late 1990s Wisconsin soybean farmers eagerly adopted Roundup Ready crops genetically engineered by Monsanto to be immune to the effects of Roundup herbicide and other weed-killing pesticides containing glyphosate. All of a sudden, farmers could spray entire soybean fields and eliminate weeds without harming the crop. Controlling weeds became faster and simpler, and steadily rising costs stabilized.

In the year 2000, a single application of glyphosate achieved season-long control on most Roundup Ready soybean fields. Fast-forward to crop season 2021 and the average Wisconsin soybean field will likely be treated with about three different herbicides. Plus, the dose of glyphosate needed to control weeds has risen 15%.

What happened? The increase in herbicide use has been driven by the spread of herbicide-resistant weeds. On many farms, growers are contending with three different resistant weeds. Resistance develops when herbicides are applied repeatedly. This leads to what is called the “pesticide treadmill,” where more applications and more herbicides are needed to successfully control weeds. Now more than 40 types of weeds are resistant to glyphosate.

The pesticide-seed-biotech industry has responded by moving more herbicide-resistant genes into the most popular soybean, corn and cotton varieties. This response has locked farmers into weed management systems progressively more dependent on herbicides. This strategy may buy a little time, but it comes at increasingly high costs to farmers, rural communities and possibly public health.

Herbicide use and costs are increasing. Seed price inflation has reached historic proportions. A transfer of income per acre is occurring from farmers to pesticide-seed companies. More herbicide drift and damage is being reported to nearby crops, backyard gardens, shelter-belts, orchards and iconic trees.

Herbicides known to raise the risk of reproductive problems and adverse birth outcomes account for much of the increase in herbicide use in the last five years. The use of dicamba and 2,4-D is rising the fastest — two herbicides also classified as possible human carcinogens by the International Agency for Research on Cancer. Is this triggering more frequent and/or more serious adverse impacts on birth outcomes and children’s development? We are part of Heartland Health Research Alliance (HHRA), an organization composed of scientists, doctors, health care delivery professionals, communications and policy experts.

Our current flagship project, the Heartland Study, will enroll 2,000 mother-infant pairs early in pregnancy. We will quantify herbicide levels in urine, search for genetic changes and determine whether those women most heavily exposed to herbicides were more likely to have difficult pregnancies or deliveries, or give birth to newborns with developmental problems or birth defects. The Gundersen Medical Center in La Crosse is among the hospitals in the Midwest participating in the Heartland Study.

We are acutely aware of the weed-management challenges facing Wisconsin farmers and hope to generate new science that will help guide changes in weed control systems sufficient to prevent adding another problem to the list.

We suggest four concrete steps in a just-published commentary entitled “Novel Strategies and New Tools to Curtail the Health Effects of Pesticides.”

First, studies supporting EPA pesticide regulatory decisions should be carried out by scientists not working for or aligned with pesticide manufacturers. This important research should be funded through grants to universities and public research institutions and paid for via pesticide registration fees.

Second, we need to invest more resources in measuring pesticide levels in people. Biomonitoring is by far the most accurate way to track changes in human exposures over time and across regions. Accurate estimates of real-world exposures are especially vital when, like today, overall pesticide reliance is rising and big changes are occurring quickly in the mix of pesticides farmers apply and people are exposed to.

Third, scientists are making rapid progress in identifying the mechanisms through which exposure to a pesticide can lead to adverse health outcomes, yet the EPA pays almost no attention to, nor places much weight on, results from cutting-edge scientific methods. This bias against new science must end.

Fourth, we must do a better job integrating scientific tools and insights from multiple disciplines into pesticide risk-assessments. For example, new approaches will deepen understanding of how prenatal pesticide exposures can disrupt fetal development and/or undermine children’s development. Advances in epidemiology can be accelerated through direct measures of exposure via human biomonitoring, coupled with the use of genomics to more effectively track impacts of rising exposures on new and specific markers of disease.

Finally, changes in weed management systems also have to align with other national needs. New, promising policies are under consideration in Washington, D.C., to enhance soil health and stabilize the climate by sequestering more carbon in the soil and in the plants and trees rooted in it. Significant progress is most likely if novel policies are crafted that also support integrated weed management systems. If they do not, they will be a hard sell to farmers.

Charles Benbrook is the executive director of the Heartland Health Research Alliance and earned a Ph.D. in agricultural economics from the University of Wisconsin-Madison. He has published widely on weed control and herbicide safety.

Thomas Green chairs the boards of the IPM Institute of North America and the Heartland Health Research Alliance. He is a certified crop advisor with 45 years of experience in agriculture and integrated pest management and holds a Ph.D. in entomology from the University of Massachusetts.

Share your opinion on this topic by sending a letter to the editor to tctvoice@madison.com. Include your full name, hometown and phone number. Your name and town will be published. The phone number is for verification purposes only. Please keep your letter to 250 words or less.