By laying sheets of plastic across their fields, farmers can bring crops to market faster while reducing their vulnerability to many blights (SN: 12/13/97, p. 376). On the negative side, however, this polymer mulch creates impermeable surfaces over more than half of a planted field. That significantly increases the amount of rain and pesticides that runs off into nearby lakes and streams (SN: 9/25/99, p. 207). A new study on tomato fields shows that this runoff can kill fish, clams, and other aquatic life.
Although farmers apply many different agricultural chemicals to tomatoes, copper-based pesticides are among the most popular, says Andrea M. Dietrich, an environmental engineer at Virginia Polytechnic Institute and State University in Blacksburg. To kill the bacteria and fungi responsible for several major blights, farmers routinely use up to 3 pounds of copper salts per acre per week throughout the growing season. Unfortunately, she notes, a lot of the copper runs off into