To get the facts, we talked to Eric Prostko, Ph.D., Extension Weed Specialist and Professor at University of Georgia in the College of Agriculture and Environmental Sciences.
1. Peanut farmers do not apply glyphosate during the growing season.
As most people know, peanuts are a legume and grow underground (hence the nickname “groundnut”). Peanuts grow differently than other nuts that grow on trees. Almonds, walnuts and pistachios are tree nuts, for instance.
Some people worry about peanuts and the use of glyphosate (Monsanto’s Roundup-branded agricultural herbicide) and its effects on the soil. They ask, since peanuts mature underground, can’t the soil be contaminated with left-over glyphosate from last year’s crops?
“It is important to understand that glyphosate is not used on peanuts during the season, because it is not a “’Roundup-Ready crop,’” according to Dr. Prostko. “Growers do not apply glyphosate on peanuts during the growing season, but some farmers use glyphosate to manage weeds prior to planting.”
Dr. Prostko explains about two kinds of tillage practices used by Georgia’s farmers: conventional and reduced or strip-tillage. Using conventional tillage prior to planting, a farmer churns up (tills) the ground to receive the seeds. This tilling process gets rid of the weeds so herbicides such as glyphosate are not needed to clear the field of unwanted weeds.
Reduced or strip- tillage is a practice of minimizing soil disturbance and allowing crop residue, stubble or weeds to remain on the ground. Dr. Prostko said farmers who practice reduced or strip-tillage often use glyphosate to manage unwanted weeds prior to planting season.
“About 25 percent of our crop in Georgia is reduced/strip- tillage crop and would likely get a pre-plant application of glyphosate. That could go on anywhere from thirty days to one day before planting,” said Dr. Prostko.
2. Peanuts do not readily absorb glyphosate for two main reasons.
“First, glyphosate readily attaches to the soil,” said Dr. Prostko. “There’s an important distinction to make when talking about glyphosate and the soil: Glyphosate is adsorbed to soil particles, not absorbed.”
Adsorption, according to Merriam-Webster’s dictionary, is when a substance adheres to the surface of solid bodies or liquids it comes in contact with (in our case, soil). However, to absorb means to take in something in a natural or gradual way.
“So adsorbing or attaching strongly to the soil is a good thing because once glyphosate enters the soil, it is essentially unavailable to plants due to its very high affinity for soil. I could spray glyphosate today and plant tomorrow and the glyphosate does not affect the crop,” said Dr. Prostko.*
When glyphosate is used, it not only attaches to the soil, but also undergoes microbial degradation, as well. Glyphosate degradation is measured in half-lives, or the time it takes for half of the herbicide to be degraded.
“Glyphosate has an average half-life of 47 days. Every 47 days, the glyphosate in the soil is halved. The half-lives continue until there is such a small amount, it is very hard to detect,” said Dr. Prostko.
But what about peanut crops that are planted in rotation with another crop that is “Roundup Ready” and sprayed with glyphosate throughout its growing season?
“If you take a year,” said Dr. Prostko, “with glyphosate degrading for seven to eight half-lives in a year’s time, the glyphosate levels are going to be very, very, very low. Again, it’s tightly bound to the soil, so it’s not likely to be at a concentration level that will have an effect on anything.”
3. The EPA’s Cancer Assessment Review Agency found no link between glyphosate exposure and cancer.
Several studies, conducted by agencies in the U.S., such as the Environmental Protection Agency (EPA) and international agencies, such as the International Agency for Research on Cancer (IARC), explored a potential link between glyphosate and cancer.
In 2015, the Cancer Assessment Review Committee (CARC) evaluated all available studies and examined the association between glyphosate exposure and one or more cancer outcomes. Based on the weight of evidence at this time, there is no support for a relationship between glyphosate exposure and cancer.
“Overall, it’s generally agreed that glyphosate is one of the environmentally-friendliest herbicides available to farmers,” said Dr. Prostko. A recent (2017) risk assessment by the U.S. EPA concluded that glyphosate is not likely to be carcinogenic to humans. The Agency’s assessment found no other meaningful risks to human health when the product is used according to the pesticide label**
* A comprehensive study on glyphosate backs this statement up. Giesy, John P.; Dobson, Stuart; Solomon, Keith R.; “Ecotoxicological Risk Assessment for Roundup ® Herbicide,” Review of Environmental Contamination and Toxicology, (2000) Volume 167, pages 35-120.
**https://www.epa.gov/pesticides/epa-releases-draft-risk-assessments-glyphosate