Pesticides are often sprayed on fruit as it is growing, to ward off pests. However, evidence has shown that it is only a matter of time before superior microbes evolve so they are immune to such poisons. If humans are to keep up with microbes, they will have to continue to develop new pesticides. The outlook is dim because one can only produce so many different pesticides. It also involves a long and difficult process to develop new sprays.
Natural selection is at work in microbes as they constantly try to thwart human pesticides.
They have developed over millions of years to use methods to make fruit objectionable to larger organisms. They will continue to do so. Humans will not be able to keep up with the evolutionary game because of the constant evolution of the microbes.