All pesticides have regulations associated with them, and what are called harvest intervals. Basically, pesticides are designed to be rain-fast (stay in the plant and not get washed off), but not 'too' stable that they never degrade. These harvest intervals mean that each pesticide has a set number of days before the plant is to be harvested that it can be sprayed. So, for example, a harvest interval of 3 days means the grower can use it three days before the plant is due to be harvested, and laboratory tests have confirmed that by the time it is harvested/eaten, the pesticide is now at a sufficiently low concentration that it is (effectively) harmless.
However, this does not factor in bacteria, fungi, insects, faecal matter, etc. These plants could have been handled by pickers who didn't wash their hands, be somewhat mouldy (e.g. Botrytis), have had a bird crap on them, or simply be covered in dirt... so in this respect, while you're definitely below the maximum residue limit (MRL) for pesticides, it's still better to be safe.
If you don't wash though, you're probably still safe, but really, what's the harm.