This information came from Mercola.com online newsletter:

Of the 43 different fruit and vegetable categories tested by the Environmental Working Group and included in their Shoppers’ Guide to Pesticides in Produce, these 12 fruits and vegetables had the highest pesticide load, making them the most important to buy or grow organic:

• Peaches
• Apples
• Sweet bell peppers
• Celery
• Nectarines
• Strawberries
• Cherries
• Lettuce
• Grapes (imported)
• Pears
• Spinach
• Potatoes

In contrast, these foods were found to have the lowest residual pesticide load, making them the safest bet among conventionally grown vegetables:

• Broccoli
• Eggplant
• Cabbage
• Banana
• Kiwi
• Asparagus
• Sweet peas (frozen)
• Mango
• Pineapple
• Sweet corn (frozen)
• Avocado
• Onion