Chopped and Processed Vegetables
Bland vegetables that contain no other ingredients, that are chopped or cut may be used provided they are insect free and are thoroughly washed before use, eg; carrots, cabbage, celery and lettuce.

Sharper flavoured chopped or shredded vegetables may not be used unless under reliable kashrut supervision. eg; capsicums, onions and radishes.  Even citrus fruits come under this ruling.

Please watch for mixed salad bags, which may contain sharp vegetables.