Nedarim 57 - I am not eating this fruit!
If one vows that he will not eat specific fruit, or that they are forbidden to him like a sacrifice, then even if he exchanges them for something else, or if something grows from them, this, too, is forbidden. When he compared his prohibition to sacrifice, he implied the same laws. Just as for a sacrifice - its exchange and its fruit (offspring) are forbidden - so too the fruit he forbade on himself.
However, if he vows against a specific type of fruit, then he can exchange it for something else and eat that. This is true for fruit whose seeds decompose in the ground. But those that partially remain, such as onions, are forbidden even as offshoots.
If one is upset with his wife's going to visit her family's home, and vows that any benefit from him is forbidden to her in case she does go, we need to look at time limits. If he said that his vow was until Passover, she has to watch not to go before Passover, or not to derive any benefit from him. But if he said that the benefit is forbidden untill Passover if she goes anytime this years, until Sukkot (which is seven months later), then if she still plans to go, she should be careful not to derive any benefit from him before Passover, because is she finally went, she would violate his vow retroactively.
Art: Still life with fruit bowl and lemons by Paul Gauguin