• Professor of Crop Science, N.C. State University.
• Associate Professor, Dept. of Crop Science, N.C. State University, 1993-1999.
• Asst. Professor, Dept. of Crop Science, N.C. State University, 1987-1993.
• Research Scientist, USDA-ARS, Stoneville, Miss., 1984-1987.
• Earned Ph.D. from Univ. of Ga.; M.S. from Univ. of Delaware and B.S. from State Univ.
of New York.
Have you ever Googled “Cotton Pesticides” or “Cotton Insecticides”? If you do, you will find statements like, “of all insecticides used globally each year, the estimated amount used on traditional cotton is 25 percent (of the total).” Or something like, “in 1992, 600,408 tons of herbicides, insecticides, fertilizers, fungicides and other chemicals were used to produce cotton in the six largest cotton-producing states.” And also, “the number of active ingredients in pesticides found to cause cancer in animals or humans is 107. Of those active ingredients, the number still in use today: 83.”
All of these statements have references that date back to the 1990s. While some of these statements may have had some truth at the time, we know that much has happened in cotton production technology since the 1990s. I will address some of the technological advances that have been made in cotton production from the North Carolina perspective and will att-empt to prove that such statements are no longer true.
The eradication of the boll weevil has caused a drop in the number of insecticide applications from 10 or more a season in North Carolina to only a few. In fact, cotton acreage in the state was below 100,000 acres before eradication, while last year the acreage was about 550,000, down from a high of nearly one million acres a few years back.
In addition to eradication of the boll weevil, the chemistries used in present production have changed drastically. The LD50 values have dropped considerably from about 20 years ago when compared to the insecticides used today.
In 1979, there were 15 insecticides recommended for use in the North Carolina Agricultural Chemicals Manual (see table). The mean LD50 in rats was 479 and a median of 42 mg/kg body weight. That means it would take an average of 479 kg/kg body weight to kill one-half of the population. In 2010, there were 53 insecticides recommended with a mean LD50 in rats 1,828 and a median of 623 mg/kg body weight, or decreases in toxicity of 381 and 1,483 percent based on the mean and median, respectively. In 1979 and 2010, the percentage of chemicals with a LD50 of less than 50 was 60 and 17 percent, respectively.
Clearly, the mammalian toxicity of today’s insecticides has been drastically reduced. In addition, the environmental persistence of present-day chemistries is greatly shortened.
More recently, the development of transgenic cotton that contains Bacillus thuringiensis (Bt) and resistance to herbicides has further reduced pesticide use in cotton production. Late season bollworm damage to Bollgard II and WideStrike cotton lines was less than 0.5 percent in the period from 2005 to 2009 as indicated by more than 700 boll damage surveys of producer-managed cotton fields.
These transgenic lines also have high resistance to fall and beet armyworms, European corn borers and loopers. In addition, glyphosate (Roundup, Touchdown, etc.), the most widely used over-the-top herbicide in cotton, has an extremely low toxicity level (LD50 = 5,600) and has a very low persistence in today’s environment.
The take-home message is that new technologies have greatly reduced the environmental impact of cotton production, but we need to study how they’re integrated into the way we manage the crop at a regional level. Success will depend on research in the many and varied environments across the Cotton Belt that are tied with effective Extension programs.
Has cotton cleaned up its act? Yes, the ability to produce a crop with much lower environmental impact is a reality.
Can we do better? Yes, fear no weevil. Using our intellect and imagination, the future of cotton can be greener than we ever thought possible.
Randy Wells is a professor of crop science at North Carolina State University. Contact him at (919) 515-3667 or firstname.lastname@example.org.