SAN FRANCISCO (AP) — California is tightening the strictest rules in the nation on a pesticide that is popular with farmers over new health concerns, officials said Friday. Farmers use chlorpyrifos (klor-PHIR-e-fos) to kill pests that attack a wide variety of crops like grapes, almonds and cotton grown in California, the nation's agricultural leader, as well as across the country. State officials are taking steps to put it on a list of chemicals known to be harmful to humans and to also increase the distance from schools and homes in which farmers can apply. The moves run contrary to a decision by Scott Pruitt, the administrator of the U.S.