Tag: 上海现在有海选的场子吗


first_imgGeorgia farmers are using a new way to grow cotton that keeps bugs at baywhile protecting the environment. They’re growing a new type of cotton, called Bt cotton, that fights some insectswhile it grows. Phillip Roberts, an entomologist with the University of Georgia ExtensionService, expects Georgia farmers to plant about a third of the 1997 cotton crop to Btvarieties. Farmers include Bt cotton, Roberts said, in an overall insect-control methodcalled integrated pest management. IPM programs use all sorts of natural controls, including Bt cotton andbeneficial insects, instead of chemicals to keep insects from harming the crop. Cottongrowers may still have to use some pesticides, but only as a last resort. IPM helps farmers stay on friendly terms with people who live around them,too. It can cut down on the number of times farmers must spray pesticides. Neighborslike that. Bt cotton can cut out even more spraying. It produces its own natural toxin thathelps control certain insects on the plant. Scientists took a toxin-producing gene from bacteria called Bacillusthuringiensis (Bt). They inserted it into the new cotton plant that takes its name. The naturally produced toxin helps control insects. “Bt cotton and IPMprograms don’t guarantee ‘no sprays,'” said Steve Brown, an extension cottonagronomist. “But they can dramatically decrease the number of applications required.” Killing bugs with the Bt toxin isn’t new. Many gardeners use it, too.Laboratories collect the toxin and include it in foliar sprays for garden plants. The toxinis the same. Only the delivery method differs. Now that the Boll Weevil Eradication Program has banished weevils fromGeorgia cotton fields, Roberts said farmers can really take advantage of the Bttechnology. “Regular cotton varieties might require six or seven pesticide applications in agiven year to control insects,” he said. “A field of Bt cotton right next to the regularvariety may only need two or three applications for the same amount of insect control.” One concern many people have is that insects may become resistant topesticides. Gary Herzog, a research entomologist at the Coastal Plain ExperimentStation, said IPM and Bt cotton can slow that process. Herzog has studied insect pesticide resistance trends since 1979. “Usually, a particular chemical can be widely used for about 10 years beforeresistance shows up,” he said. Bt cotton can extend that time. Farmers don’t have to spray as often. So insectsaren’t exposed as much to the most commonly used pesticides. So it takes them longerto develop resistance. If the Bt toxin doesn’t kill all the insects, Herzog said, it still weakenssurvivors. That makes them more vulnerable to other insecticides and the beneficialinsects that prey on them. The Bt toxin doesn’t affect the cotton fiber. It’s as strong and long and white asthat of non-Bt varieties. Planting Bt cotton can help farmers’ profits, too. If they can grow cotton withlower cost per acre, they can make more money on the same land. Higher profits lead more farmers to grow cotton. When more cotton is sold,though, the farmer’s prices can drop. Retail cotton clothing prices can drop, too. It costs farmers more — about $33 per acre — to plant Bt cotton. Roberts andBrown said if a grower has to spray a field four or more times for bollworms, he maydo better planting Bt cotton. “Each farmer has to decide if he can control bollworms for less than the cost toplant Bt cotton,” Brown said.last_img read more