This organizational chart shows Walter’s Division in the USDA, just a short time before he quit. As the war started winding down, the Department shifted its focus back to its usual beat, boosting the yields and sales of US-grown crops. They also began looking for peacetime uses of technologies developed during the war, including the amazing new lousicide Walter’s group had worked on. Walter didn’t document his thinking about this, but various family stories and some of his publications hint that he wasn’t at all pleased with the idea of spraying DDT on crops. In one paper from 1945, he described the compound as “definitely toxic,” and argued that it might have harmful effects in the environment when used in large quantities for extended periods of time.

By mid-1946, he had left the Department and taken a job with US Industrial Chemicals in Baltimore, where he began working on improving pyrethrum-based insecticides.

June 30, 1945