The current “new era” in cotton insect control — typified by fewer insecticide applications and target-specific chemistry — has been a long time coming, beginning with the introduction of pyrethroids in the 1970s and culminating with more recent developments, such as Bollgard cotton.
“There has been a steady decline in the past 20 to 30 years in the number of insecticide applications made on cotton,” says Ron Smith, Auburn University Extension entomologist.
Impact of pyrethroids
“The initial drop-off in insecticide applications began in the late 1970s, when pyrethroids became available to farmers.”
Prior to the introduction of pyrethroids, growers were relying on phosphates, he says. “Pyrethroids were more residual than phosphates, and they were much more effective on caterpillars. In addition, growers no longer were spraying every five days for boll weevils,” says Smith.
Cotton producers saw another tremendous drop in insecticide applications in the 1990s, with the eradication of the boll weevil, he says.
“The boll weevil was eliminated as an economic pest of cotton through the Boll Weevil Eradication Program, and that gave us a big drop in the number of applications and in the pounds of insecticides that were going out into the fields,” notes Smith.
Then, in 1996, the introduction of Bollgard cotton led to yet another decline in insect treatments. “This development hasn't been good for everyone, because we've also cut down tremendously on aerial applications and on the sales of traditional insecticides,” he says.
The changes brought about by the introduction of Bollgard are numerous, he continues. “Looking at the manufacturing sector, we're saving about 3.46 million pounds or raw materials that would have been used in the making of insecticides due to Bollgard technology. Also, we're conserving about 1.5 million gallons of fuel oil that would have been used in manufacturing traditional insecticides.
“In addition, we've eliminated 2.1 million pounds of insecticidal waste that would have been created in the manufacture of insecticides. We're also transporting slightly less than one million fewer gallons of insecticides due to the advent of Bollgard technology. This alone is conserving about 600,000 gallons of fuel oil.”
In terms of grower applications, Bollgard cotton has resulted in about one million fewer pounds of insecticides being applied in fields, says Smith, and growers are making 2.5 fewer sprays per acre where Bollgard cotton is planted.
“We're also disposing of about 416,000 fewer pesticide containers, and we're saving about 41,000 10-hour farm work days and 2,100 10-hour days of aerial applications. Farmers also are conserving about 2.4 million gallons of fuel and 94 million gallons of water that would have been used in the application of insecticides.”
The new cotton insecticides and materials that still are in the research pipeline are very selective and target-specific, says Smith.
“Most of these products will target the big, sucking-type pests, such as plant bugs, stinkbugs and aphids. Or, they might target caterpillars. But these new materials won't be broad spectrum — they'll target one group of insects or the other, and that's something we've never seen in synthetic chemicals for cotton insect control. Up until now, most materials have been broad spectrum.”
This selectivity, he adds, is good and bad. “For the first time ever, we can take out caterpillar pests and leave lady beetles. Some of these new materials are very easy on beneficial insects. A downside, especially from the grower's perspective, is that all of these products are more expensive. But, they are safe to handle, and they're safe for the environment.”
Coverage and the timing of insecticide applications will be more important now than ever before, says Smith.
“We're moving into a new era — a more expensive era in which growers no longer will have the luxury of making preventative applications. They're going to have to know what the problem is in the field and target their spraying just to that insect.”
This will involve monitoring each field on a regular basis to determine which pest is at an economically damaging level. Once that determination is made, growers — working from a list of up to 10 different chemistries — must decide which one is best suited for eliminating one particular pest while leaving the other pests alone.
The demand for highly trained scouts, says Smith, will be more important than ever. “In the old days, it was easy to focus on one dominant pest in the field, knowing that when you reacted to one pest using broad-spectrum chemicals, you would be taking care of others as well.
“However, this new approach will require a trained professional who can go into a field and look for the pest that is most likely to pose a threat during that particular week in the growing season. That's where experience will count. Inexperienced scouts simply are not going to be what a grower needs. It's going to require an experienced person who can guide an inexperienced scout through the field.”
For the first time ever, cotton growers have chemicals with unique modes of action, says Smith. “Also for the first time ever, we can manage resistance to some degree, by alternating different chemistries with different modes of action. Before, we always had one primary group of chemicals at a time. Now, we have between eight and 12 chemical classes of insecticides that are under development.
“For that reason alone, we shouldn't have to worry as much about resistance as we have in the past.”
Unlike many broad-spectrum insecticides — which tended to work immediately on contact with the pest — many of these new chemicals are slower-acting stomach poisons, says Smith. “We will have to do a better job of applying these chemicals and making sure they're ingested. The slower-acting nature of these new chemicals also will affect how fields are monitored after spraying.
“With this new approach, some of these pests are likely to linger for a few days after the applications. So, a good rule of thumb is to wait a few days before returning to the fields to evaluate.”
Producers also won't be required to spray their cotton as often, he says. “In the past, growers typically made applications at certain intervals. In the future, a producer may go two, four or even six weeks without applying chemicals.”
Growers basically have two systems of cotton production today — the Bollgard or Bt system and the conventional system, says Smith.
“Your insect pests will depend on which system you choose. In Bt cotton, we know we'll be dealing with thrips. For awhile this year, I thought thrips might be our most damaging pest, and I'm not sure it won't work out that way.
“We also have aphids and the plant bug complex in Bt cotton. The plant bug complex would include the clouded plant bug — which caused such extensive damage this year — the tarnished plant bug and fleahoppers. We also have the stinkbug, and that's where the action is on Bt cotton today. We must do a better job of determining thresholds and knowing when to spray for stinkbugs. We're losing cotton yields to this pest.”
Thrips and aphids are common insect pests in conventional cotton, says Smith, but the primary target in conventional varieties is the bollworm and budworm.
“This is the third light year in a row for bollworms and budworms in Alabama. But we have seen some pressure this year. In surveying some of our plots, it appears that most of our problems are coming from the bollworm, although budworms are mixed into the system. We still can control bollworms very efficiently with pyrethroids.”
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