Q. Hi. I am wondering which frozen fruits/vegetables need a hechsher and which don’t. I know that frozen produce like mango and blueberries does not, but do frozen raspberries, strawberries, and blackberries require a hechsher? What about frozen green beans, cauliflower, and broccoli? I live in Ottawa, Ontario and the laws here in Canada are pretty strict about thoroughly washing produce before freezing and selling it. Thank you in advance!

A.  The cRc  Fruit & Vegetable Policy is that all freeze dried vegetables & fruits require a reliable hashgacha. Generally, The cRc web site provides a list and adds, “It is impossible to cover all of the different varieties, so if a particular product is not found on this list, please call the cRc office.”
Montreal M.K. also provides a list.
Chabad Org. Writes, “Most frozen vegetables are acceptable for year-round use (excluding Passover), as the freezing process does not pose any Halachic concerns; though you should always be on the lookout for insects which occasionally infest vegetables.
It appears that due to the strong likelihood of insect infestation in the following frozen vegetables, they should only be bought with a reliable kosher certification: broccoli, cauliflower, brussel sprouts, asparagus, cut onions, spinach, potatoes, and artichoke hearts.”
Star K in regards to Pesach maintains that, Frozen Vegetables require reliable Kosher for Passover certification since pasta blends are produced on the same equipment. Plain, frozen, unsweetened fruit pieces would be acceptable without special Passover certification. Sweetened frozen fruit pieces could be sweetened with liquid sugar or corn syrup, requiring strict Passover supervision.

I also forwarded your question to Rabbi Tsvi Heber, Director of Community Kosher – COR. This was his reply:
Frozen fruits are kosher without a hechsher. If there is an infestation issue (strawberries, raspberries, blackberries) then it can be used as a puree or in a liquid form.
 Frozen vegetables from North America can be considered kosher without a hechsher.  If there is an infestation issue (cauliflower, broccoli) then it can be used as a puree or in a liquid form.
Horav Shlomo Miller’s Shlit”a opinion is similar to the above last. However, he added, that when there is an infestation issue you may check out and inspect properly the fruits and vegetables, provided that you know how to do it. (You have to know the shape, colour and size of the infecting insects, how to make them visible and how to remove them).

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a