Strawberries can actually make your teeth whiter over time, though it is not a whitening method most people use. It will be important to rinse your mouth out immediately after eating strawberries though, just to make sure that you get rid of any surface contaminants.
There are quite a few different things which strawberries can be sprayed with and sometimes simply washing them does not get everything off.
Those who eat strawberries quite often probably notice that their teeth get progressively whiter, though perhaps not in an extremely noticeable way. While it is not considered to be a mainstream whitening method for teeth, it is still used as a home remedy by some.