For the record, this is true. Rotting fruit produces ethylene which can speed the ripening process in other fruits. English preacher and writer, John Northebrooke put these words to paper in 1577 but credits Chrysostom, a 4th century theologian. Rarely are people talking about apples. It is bad people, so the quote implies, that have a negative influence on others.  

2 Thessalonians 3:14    

Take note of those who do not obey what we say in this letter; have nothing to do with them, so that they may be ashamed.

Texts such as this one give rise to the formal practice of some churches, and the informal practice of pretty much all churches: shunning. The verse that follows includes a reminder that such isolation is to be offered with care, and for the purpose of restoration. We sometimes miss the mark on this, whether it be a formal shun or informal ignorance. A friend once told me that in her church, when you hear the words, “I’m going to say this to you with love” it is time to “look out for you are about to be hit square between the eyes.” The motivation for correcting appears, in this text, not to be so much about preserving the church but for preserving the wholeness of the individual who is disobedient. There seems to be no biblical record of Jesus refusing to associate with “disobeyers.”  In fact, Jesus spent a lot of his time with “bad apples” (e.g. Matthew 9:11) and was often criticized for it. If indeed “one bad person” spoils the rest, Jesus would have been spoiled himself.