Perspectives On Line - Winter 2002: Feature Article / "A Cotton Conundrum"
Perspectives On Line: The Magazine of the College of Agriculture and Life Sciences

NC State University

Winter 2002 Contents Page Features Research and Response A Cotton Conundrum Zero at the Bone College Profile Noteworthy News Giving Alumni From the Dean College of Agriculture & Life Sciences  





































The cost of those
extra insecticide applications for conventional cotton
begins to cancel out the technology fee farmers pay for Bt cotton.

But the Bt versus
conventional cotton equation is still a bit
more complicated....

































"A Cotton Conundrum" by Dave Caldwell:  For North Carolina farmers, the decision to plant conventional cotton or Bt cotton can be difficult.
Entomologist Jack Bacheler (left), a North Carolina Cooperative Extension specialist, conducts surveys and compiles information about insect damage to give farmers the facts they need to make informed decisions. (Photos by Communication Services)


onsider the attributes of genetically engineered cotton that contains a gene that produces a toxin that kills many of the caterpillars that feed on cotton. The plants contain their own insecticide, and the toxin kills only caterpillars, so the poison does not pose a danger to other animals or the environment.

For farmers, deciding what type of cotton to plant — genetically engineered or conventional — would seem to be a no brainer. Conventional cotton, after all, must be sprayed with expensive insecticide to protect it from caterpillars. Now, in North Carolina at least, the decision is turning out to be more of a head scratcher.

Genetically engineered cotton, which goes by the brand name Bollgard and is also known as Bt cotton (the poison-producing gene comes from a bacterium called Bacillus thuringiensis), has been available to cotton growers since 1996. Since that time, Dr. Jack Bacheler, an entomologist in the College of Agriculture and Life Sciences at N.C. State University, has been comparing conventional and Bt cotton.

Bacheler, who is also a North Carolina Cooperative Extension specialist, has found that for North Carolina farmers the cost of controlling insects is about the same for Bt as it is for conventional cotton. For the farmer who plants Bt cotton, Bacheler puts the average cost of insect control from 1996 through 2000 at $27.64 per acre. For the same time period, he figures it cost the farmer who planted conventional cotton an average of $27.30 per acre to control insects.

“Bt has been a pretty big technology happening for several crops,” says Bacheler. Agricultural scientists have been able to insert Bt genes into other crops in addition to cotton, and the availability of these Bt plants has been among the early successes of genetic engineering.

Bacheler points out that in 1996, when Bt cotton first became available in North Carolina, only 2 percent of the state’s cotton acreage was planted in the genetically engineered cotton. In 2001, Bt cotton was planted on 65 percent of the 930,000 North Carolina cotton acres.

Each year, Bacheler surveys large cotton growers and agricultural consultants who advise growers, asking about the kind of cotton they plant, how they control insects and what kind of insect damage they experience. He also goes into 150 to 200 cotton fields himself each year to check insect damage.

“We’re trying to quantify pest shifts since the introduction of Bt cotton,” he says. He also collects information on a variety of other aspects of cotton growing, including costs.

Bt cotton costs more than conventional cotton to begin with. Bacheler explains that a technology fee is added to the cost of Bt cotton seed. The seed can cost from two to three times as much as seed for conventional cotton.

But farmers who grow Bt cotton usually save money later in the growing season, when it comes time to apply insecticide. In North Carolina, the primary pest of cotton is a caterpillar that goes by two names — corn earworm or cotton bollworm. The insecticide in Bt cotton is effective only against caterpillars, and it is more or less effective, depending on the type of caterpillar. Bt cotton has good resistance to bollworms; it is virtually immune to damage from other types of caterpillars, and has poor resistance to yet other types. Despite the good resistance Bt cotton offers to bollworms, North Carolina farmers often have to supplement it with some insecticide sprays.

Bacheler’s surveys indicate that North Carolina farmers who plant Bt cotton average 0.7 insecticide sprays per growing season. North Carolina farmers who plant conventional cotton, on the other hand, must spray their fields an average of 2.5 times to protect their crops from bollworms. The cost of those extra insecticide applications for conventional cotton begins to cancel out the technology fee farmers pay for Bt cotton.

But the Bt versus conventional cotton equation is still a bit more complicated because, Bacheler points out, Bt cotton typically sustains less insect damage, roughly half as much, as conventional cotton. And there’s yet another fly, actually bug, in the ointment.

“The interesting thing is that in this lower spray environment [for Bt cotton], pests such as stink and plant bugs have become more prominent,” Bacheler says.

Remember, the toxin in Bt cotton is effective only against caterpillars. Stink and plant bugs, which also feed on and damage cotton, are apparently taking advantage of the absence of insecticide in Bt cotton fields. Bacheler says his surveys indicate that stink and plant bug damage appears to be increasing in North Carolina.

If stink and plant bug numbers continue to rise and farmers who grow Bt cotton find they have to spray more insecticide to control the bugs, that could tip the economic scales in the favor of conventional cotton, Bacheler says.

Bacheler’s best advice for farmers is to consider their individual circumstances. In parts of the state where insect pressure on cotton tends to be relatively mild — the area just west of Charlotte is an example, says Bacheler — farmers may be better off planting conventional cotton and avoiding the Bt cotton technology fee. In areas where bollworms tend to be a particular problem, Bt cotton may be the more economical choice, assuming stink and plant bugs are not unusually numerous. To make the decision even more complicated, Bacheler points out that the quality of different cotton varieties varies, whether the variety is Bt or conventional, so growers must also consider variety quality as they decide what to plant.

Bacheler conducts surveys and compiles information about insect damage in an effort to give farmers the information they need to make informed decisions. When it comes to deciding what kind of cotton to plant, however, his information demonstrates how difficult that decision can be.


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