USDA: Cotton farmers report declines in the effectiveness of the herbicide glyphosate

In 2016, cotton farmers began using genetically engineered (GE) cotton seeds that were tolerant of the herbicide dicamba, which controls annual and perennial broadleaf weeds.

Before the commercialization of dicamba-tolerant (DT) seeds, cotton farmers had widely adopted GE glyphosate- and glufosinate-tolerant crop varieties. As adoption rates of these herbicide-tolerant crops increased, the use of glyphosate and glufosinate also increased, particularly glyphosate.

On some fields, a small number of naturally resistant weeds, from a small number of weed species, were able to withstand glyphosate applications. Over time, these weeds bred and spread, passing on their natural resistance to the next generation.

By 2019, there were glyphosate-tolerant weeds in most cotton-producing States, leading to a reduction in the herbicide's effectiveness. Initially, farmers increased glyphosate application amount and frequency to overcome this problem, but as resistance worsened, farmers included additional herbicides, such as dicamba. Data from USDA's 2019 Agricultural Resource Management Survey showed that farmers observed declines in the effectiveness of glyphosate in all States surveyed.

Generally, there appeared to be more DT seed use where farmers reported a decline in the effectiveness of glyphosate.

However, the States with the most glyphosate-resistant weeds were not always the States with the most DT cotton. For example, a decline in the effectiveness of glyphosate was observed on about 68 percent of the planted cotton acreage in Texas, but DT seeds were planted on only 63 percent of that State's cotton acreage.

This chart appears in the July 2021 Amber Waves data feature Adoption of Genetically Engineered Dicamba-Tolerant Cotton Seeds is Prevalent Throughout the United States.