Rotation: means that a conscious decision is made to change the drug(s) used at a given time in the future i.e. every four months, after two crops, go to a winter and summer program etc. The alternative to a rotation program is a continuous program where the same drug(s) are used indefinitely, usually until a problem develops, or until a new product is introduced on the market. Shuttle programs fit into rotation programs i.e. a decision may be made to use a shuttle program (Drug A and Drug B) for the summer of 1995. For the winter program other drugs may be used in a shuttle, or only one drug.