ALWAYS buy the following produce ORGANIC (sometimes called the Dirty Dozen).
Apples
Strawberries
Grapes
Celery
Peaches
Spinach
Sweet bell peppers
Nectarines
Cucumbers
Potatoes
Cherry tomatoes
Hot peppers
Green Beans
The following may contain organophosphate insecticides, which EWG characterizes as "highly toxic".
Kale/collard greens
Summer squash
Now for the GOOD news!
The following produce bore little to no traces of pesticides are considered "Clean" and safe to eat when Organic versions are not available.
onions
avocado
pineapples
mango
mushrooms
Papaya
sweet peas
asparagus
kiwi fruit
cabbage
eggplant
cantaloupe
watermelon
grapefruit
sweet potato
sweet onions