When going apple-picking, is it safe to add to your bag an apple that’s been lying on the ground?

Absolutely not.  As Morton Satin, (the author of Food Alert! ,) points out, apples that have been lying on the ground  (called ground-tagged apples) may have become contaminated by dirt and  manure.  “As a result, they are an excellent vehicle for  the transmission of all types of pathogenic microorganisms,…”   However, as food scientist Susan Brewer explains, apples still on the tree can also become contaminated by bird feces and insects.  For these reasons, it’s important to wash apples well before consuming or cooking with them.
 
Source(s):
Food Alert! by Morton Satin, 2008.
 
Susan Brewer, Ph.D. University of Illinois, Department of Food Safety and Human Nutrition