ADDIS — A tiny pest called the pasture mealy bug is threatening Louisiana's sugar cane crop just weeks before harvest and farmers say they've never seen anything like it before.The insect introduces a toxin into the sugar cane plant, causing leaves to turn yellow. More than 10 parishes have already seen effects from the pest this year."With yellowing, we can't go through the process of photosynthesis and keep the plant healthy," said Turner Grah…