MILWAUKEE (AP) - The U.S. Department of Agriculture is opening the door to commercial sales of genetically engineered corn and soybean seeds that are resistant to a weed killer best known as an ingredient in the Vietnam War-era herbicide Agent Orange. The weed killer is called 2,4-D. It's legal and commonly used in the U.S. by gardeners, and scientists don't believe it was responsible for the health problems linked to Agent Orange. The USDA, which has oversight over the seeds and not the herbicide, released an environmental impact statement Friday. It says the biggest risk from the seeds is that greater use of the herbicide could hasten the development of herbicide-resistant weeds. But the agency also says resistance is inevitable because the herbicide is already the third most-used weed killer in the U.S.