When to buy organic and foods lowest in pesticide

I find it very helpful to know what to shop for when I go to the grocery.  Sometimes, I have to buy fruits and vegetables that are not organic.  When should I not buy the food item at all unless I can find the organic option?  Here is a list of the "Dirty Dozen Plus" and the "Clean 15" that are safe to consume even with limited pesticides.

The following information comes from the website for the Environmental Working Group, a non-profit dedicated to informing the public in order to protect public health and environment. 

http://www.ewg.org/foodnews/summary/

Dirty Dozen Plus^™

Buy these organic

1

Apples

2

Celery

3

Sweet bell peppers

4

Peaches

5

Strawberries

6

Nectarines
– imported

7

Grapes

8

Spinach

9

Lettuce

10

Cucumbers

11

Blueberries
– domestic

12

Potatoes

Plus

+

Green beans

+

Kale/Greens

+ May contain pesticide residues of special concern

Clean 15^™

Lowest in Pesticide

1

Onions

2

Sweet Corn

3

Pineapples

4

Avocado

5

Cabbage

6

Sweet peas

7

Asparagus

8

Mangoes

9

Eggplant

10

Kiwi

11

Cantaloupe
- domestic

12

Sweet potatoes

13

Grapefruit

14

Watermelon

15

Mushrooms