Each year they release the Dirty dozen and Clean 15 Lists. These produce items have shown to have the higest levels of pesticide residue (even after being washed and peeled). So if you're on a tight budget and can't afford to purchase all organic produce then learn these lists (in order of importance).
2013 Dirty Dozen
spend extra money for organic on the items below:
7. Sweet Bell Peppers
8. Nectarines (imported)
11. Cherry Tomatoes
12. Hot Peppers
There are two additional items they are calling the Dirty Dozen Plus. You should also consider purchasing organic whenever possible:
1. Summer Squash
2. Leafy Greens (Kale and Collards)
2013 Clean 15 List
These items were found to have the least amount of pestisides. If you are on a tight budget then the Clean 15 can help save your money by buying conventional produce.
1. Sweet Corn (I wish I could take this one off the list. Most corn in the US is genetically modified (GMO).