The vision of airplanes rumbling slowly over San Francisco, spraying a pesticide mist on parks and playgrounds, has now mobilized one of the most effective lobbying groups in the world. Moms. The California Department of Food and Agriculture's plan to eradicate the light brown apple moth with aerial spraying over the city this summer was already in an uphill fight. But when 100 or so mothers and kids showed up at City Hall on Monday afternoon with signs like "Keep Your Spray Off My Baby," it was clear that the battle had entered a new phase. "Nothing gets people more...