How do you know if your food is covered in pesticides? Can you afford to buy everything organic? 

Some fruits and vegetables are a lot cleaner than others, according to tests of pesticide residues found on common produce items. So if you're worried about pesticides, this list can help you decide when to skip the organic produce aisle -- or not.

The U.S. Department of Agriculture maintains a database of pesticide residue found on produce. Its findings indicate 178 different pesticides and pesticide residues on the thousands of samples tested, even after the food was washed.

The Environmental Working Group, a non-profit that performs research and advocacy on pesticides and other chemicals that can harm health, analyzes the tests by the USDA, and provides a shopper's guide of the cleanest and most contaminated fruits and vegetables. 

From EWG's list, these are the cleanest fruits and vegetables: